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  • 550 - Earth sciences
  • Armut
  • English  (164)
  • Spanish  (1)
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  • 1
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    Empirical Analysis of Poverty Dynamics (2021)
    Peter Lang International Academic Publishers
    Details
    Publication Date: 2024-04-11
    Description: The empirical analysis of poverty over time is still severely constrained by the available survey data in developing countries. In the past, this has led to a neglect of certain aspects of poverty dynamics or even biased assessments of poverty dynamics. This book explicitly takes into account the present data limitations, proposing alternative methods for the empirical analysis of poverty dynamics. The work addresses both the problems related to limited data in the analysis of macro-level (or national) as well as micro-level (or household) poverty dynamics. The proposed methods are applied to survey data from various sub-Saharan African countries. As these countries do not only have the most limited economic survey data but also show the highest poverty rates in the world an accurate understanding of the underlying poverty dynamics seems to be most important for these countries.
    Keywords: Africa ; Analysis ; Armut ; Case ; Dynamics ; Empirical ; from ; Günther ; Inflation Inequality ; Poverty ; Pro-Poor Growth ; Saharan ; Schwarzafrika ; Studies ; Vulnerability to Poverty ; With ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPA Political science and theory ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPH Political structure and processes ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies
    Language: English
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  • 2
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    Poverty and Distributional Impact of Economic Policies and External Shocks (2021)
    Peter Lang International Academic Publishing Group
    Details
    Publication Date: 2024-03-29
    Description: Economists have had much to say about the impact of economic policies on growth, but little on their distributional consequences and poverty impact. The reorientation of development policy from structural adjustment to poverty reduction as the central objective thus called for new tools to examine distributional change. This book analyzes the poverty and distributional impact of policy changes and external shocks in three case studies from Latin America: Trade liberalization in Colombia and Brazil, and the gas boom in Bolivia. It uses an innovative approach that combines computable general equilibrium and microsimulation models. The country applications illustrate that distributional consequences depend very much on the nature of the shock or policy change as well as the characteristics of the country in question. The book issues a warning against policy prescriptions being based on oversimplifying assumptions and models.
    Keywords: America ; Approaches ; Armut ; Case ; Combining ; Distributional ; Economic ; External ; from ; Impact ; Income distribution ; Inzidenz (Wirtschaft) ; Kolumbien ; Latin ; Macro ; Macro-micro model ; Micro ; Microsimulation ; Policies ; Poverty ; Resource boom ; Shocks ; Studies ; Three ; Trade policy ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPA Political science and theory ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCA Economic theory and philosophy ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCF Labour / income economics ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies
    Language: English
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  • 3
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    Measurement of Poverty, Undernutrition and Child Mortality (2021)
    Peter Lang International Academic Publishers
    Details
    Publication Date: 2024-03-29
    Description: Although the world has seen a strong increase in global incomes in the last two decades and consequently a decline in global poverty rates, the number of persons living in absolute poverty remains on unacceptably high levels. Besides rising incomes can not distract from the fact that resources to fight global problems remain scarce. These resources have to be devoted to the fight against different global problems like the fight against communicable and non-communicable diseases (especially HIV/AIDS and Malaria) or the fight against global warming. The main precondition to achieve the best results with these limited resources is a good knowledge about the determinants and the best policies to fight each problem. But before being able to analyze the determinants of the different global problems and especially of poverty, it is of fundamental importance to find the right indicators for each phenomenon. This book contributes to the discussion of appropriate poverty indicators for the different dimensions of poverty like income poverty, undernutrition and child mortality and proposes a multidimensional poverty indicator that takes the income distribution into consideration.
    Keywords: Armut ; Child ; Empirical Analysis of Poverty ; Entwicklungsländer ; Human Development Index ; Kindersterblichkeit ; Measurement ; Misselhorn ; Mortality ; Multidimensional Poverty Measures ; Poverty ; Undernutrition ; Undernutrition Measurement ; Unterernährung ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPA Political science and theory ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPH Political structure and processes ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCS Economic systems and structures ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPA Political science and theory ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPH Political structure and processes ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCS Economic systems and structures
    Language: English
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  • 4
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    Poverty, Inequality and Migration in Latin Amerika (2021)
    Peter Lang International Academic Publishers
    Details
    Publication Date: 2024-04-07
    Description: The causes and consequences of high inequality in incomes, assets, and many aspects of well-being in Latin America have recently (re-)emerged as a central research and policy issue. However, many open questions remain that will be dealt with in the contributions to this volume. First, the linkages between growth, inequality, and poverty in Latin America need further clarification. More analyses at the country and even sub-national level are required to understand these complex relationships and their most important determinants. Of particular relevance is to examine these relationships in the Latin American context of high economic instability with recurrent economic and financial crises, particularly in the 1990s. Secondly, measuring and addressing poverty remains a critical research area, in particular non-monetary including subjective indicators of well-being often tell a different story that needs to be considered when analyzing poverty trends and determinants. Lastly, the poverty/inequality issues need to be considered in an economic environment, where trade, migration, and economic integration are of particular importance. Thus the role of trade and migration in generating, sustaining, or reducing inequalities between and within countries is an area that requires further analysis.
    Keywords: Amerika ; Armut ; Economic Development ; Einkommensdisparität ; Inequality ; Klasen ; Lateinamerika ; Latin ; Latin America ; Migration ; Poverty ; thema EDItEUR::J Society and Social Sciences::JH Sociology and anthropology ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPA Political science and theory ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPH Political structure and processes ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies
    Language: English
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  • 5
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    Economic Growth, Biodiversity Conservation, and the Formation of Human Capital in a Developing Country (2021)
    Peter Lang International Academic Publishing Group
    Details
    Publication Date: 2024-03-27
    Description: Can education play a role in fostering economic growth and simultaneously decrease pressure on forests? The aim of this study is to show that it can. Human capital formation is a key element in a development strategy that includes natural resource conservation within the framework of sustained economic growth and poverty alleviation. Consequently, it is not by chance that Guatemala is experiencing both minimal per capital income growth and high deforestation while having one of the lowest educational levels in Latin America. However, since many assumptions about educational benefits are controversial and many aspects depend on broader issues, human capital formation can only be one piece in a multidimensional puzzle. This study is organized into three parts, each one of which can be read independently: first, a macroeconomic assessment of education and other factors involved in the country’s growth trajectory; second, a rural analysis indicating the root causes of deforestation and the role education can play to slow down habitat loss; third, the highlighting of some elements indispensable to reform and to subsequent improvement of the quality of rural schooling.
    Keywords: Armut ; Bildungspolitik ; Biodiversität ; Biodiversity ; Capital ; Case ; Conservation ; Country ; Developing ; Economic ; Formation ; Forstwirtschaft ; Growth ; Guatemala ; Guatemala ; Human ; Löning ; Natürliche Ressourcen ; Wirtschaftliches Wachstum ; Wirtschaftswachstum ; Zentralamerika ; thema EDItEUR::D Biography, Literature and Literary studies::DS Literature: history and criticism::DSB Literary studies: general ; thema EDItEUR::J Society and Social Sciences::JN Education ; thema EDItEUR::J Society and Social Sciences::JP Politics and government ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCG Economic growth ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCV Economics of specific sectors::KCVG Environmental economics ; thema EDItEUR::K Economics, Finance, Business and Management::KJ Business and Management
    Language: English
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  • 6
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    Empirical Analysis of Determinants, Distribution and Dynamics of Poverty (2021)
    Peter Lang International Academic Publishing Group
    Details
    Publication Date: 2024-03-29
    Description: Poverty and inequality persist in many dimensions in the developing world. In order to understand the determinants of poverty and its distribution between and within countries, it is necessary to know its dimensions and the channels through which poverty and inequality affect human well-being. This book analyzes the spatial disparities of the outcomes and determinants of poverty, the interdependencies of dimensions of poverty, the distribution of progress in human development over the population and the dynamics of poverty risk over time. The study takes into account the global spread of poverty. Based on cross-country comparisons of countries from Africa, Latin America, and South Asia, this study does not only consider on average outcomes and determinants of different indicators of human well-being, but also examines their distribution between and within countries.
    Keywords: AIDS ; Analysis ; Armut ; Child Mortality ; Determinants ; Distribution ; Dynamics ; Empirical ; Entwicklungsländer ; Harttgen ; Household's Vulnerability ; Poverty ; Poverty ; Pro-Poor Growth ; Socio-economic effect of HIV ; Undernutrition ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPA Political science and theory ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPH Political structure and processes ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCM Development economics and emerging economies ; thema EDItEUR::K Economics, Finance, Business and Management::KC Economics::KCS Economic systems and structures
    Language: English
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  • 7
    Monograph available for loan
    Monograph available for loan
    Stuffed and starved : from farm to fork ; the hidden battle for the world food system (2013)
    London : Portobello Books
    Details Availability
    Keywords: Lebensmittelproduktion ; Lebensmittelversorgung ; Ernährungssicherung ; Hunger ; Fehlernährung ; Mangelernährung ; Armut ; Unterprivilegierung ; Lebensmittelproduktion ; Lebensmittelindustrie ; Globalisierung ; Agrarpolitik ; Wirtschaftspolitik ; Welternährung ; Landwirtschaft ; Bevölkerungswachstum ; Ernährungssicherung
    Type of Medium: Monograph available for loan
    Pages: IX, 418 S. , Ill., graph. Darst. , 20 cm
    Edition: Revised 2. edition
    ISBN: 1846274796 ((pbk)) , 9781846274794 ((pbk))
    Language: English
    Branch Library: PIK Library
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  • 8
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    Source modelling of the M5-6 Emilia-Romagna, Italy, earthquakes (May 20-29, 2012). (2013)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: On 2012 May 20 and 29, two damaging earthquakes with magnitudes Mw 6.1 and 5.9, respectively, struck the Emilia-Romagna region in the sedimentary Po Plain, Northern Italy, causing 26 fatalities, significant damage to historical buildings and substantial impact to the economy of the region. The earthquake sequence included four more aftershocks with Mw ≥ 5.0, all at shallow depths (about 7–9 km), with similar WNW–ESE striking reverse mechanism. The timeline of the sequence suggests significant static stress interaction between the largest events. We perform here a detailed source inversion, first adopting a point source approximation and considering pure double couple and full moment tensor source models. We compare different extended source inversion approaches for the two largest events, and find that the rupture occurred in both cases along a subhorizontal plane, dipping towards SSW. Directivity is well detected for the May 20 main shock, indicating that the rupture propagated unilaterally towards SE. Based on the focal mechanism solution, we further estimate the co-seismic static stress change induced by the May 20 event. By using the rate-and-state model and a Poissonian earthquake occurrence, we infer that the second largest event of May 29 was induced with a probability in the range 0.2–0.4. This suggests that the segment of fault was already prone to rupture. Finally, we estimate peak ground accelerations for the two main events as occurred separately or simultaneously. For the scenario involving hypothetical rupture areas of both main events, we estimate Mw = 6.3 and an increase of ground acceleration by 50 per cent. The approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard, bearing the potential for large aftershocks or even a second main shock.
    Keywords: 550 - Earth sciences
    Language: English
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  • 9
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    A Geodetic Study of the 23 October 2011 Van, Turkey earthquake (2013)
    In:  Tectonophysics
    Details
    Publication Date: 2020-02-12
    Description: The Van (Eastern Anatolia, Turkey) earthquake occurred on Sunday, October 23, 2011 with a moment magnitude of 7.2. The tectonics of this region is characterized by strike–slip faulting on the Bitlis Suture Zone, and thrusting in the Zagros fold and thrust belt. Using high-rate (1 second) GPS data from permanent GNSS stations from the CORS-TR network, co-seismic displacements of eleven stations were determined using precise point positioning during this earthquake. We used the time series of coordinate changes for fourteen CORS-TR stations, and calculated the crust movements before and after the earthquake. According to the PPP solutions computed using high frequency GPS data to determine the co-seismic motions of stations, we conclude for the Van earthquake an occurrence time of 10:41:22 (UTC). No pre-seismic horizontal movement of stations at the level more than 5 mm before the earthquake could be observed. That means that no kinematic warning or prediction before the earthquake exists. Along an east–west horizontal line north of the Van Sea with a length of about 100 km, the northern part of this line experienced extension of 0.2–1 ppm in a NW–SE direction. The southern part experienced N–S shortening of 0.5–1.5 ppm. The N–S shortening we estimated geodetically matches well with the N–S shortening and thrust focal mechanism derived independently using seismic data by the USGS. Co-seismic surface displacements derived from the GPS data are consistent with the teleseismic source model given by the USGS. The geodetic source model derived from the GPS data reproduces the same moment magnitude and centroid as the teleseismic model, but shows a higher spatial resolution of the slip distribution. We also analyzed the post-seismic surface displacements derived from the GPS data within the first two weeks after the mainshock. No reasonable slip distribution on the co-seismic fault plane could be found, indicating that the sources for the early post-seismic deformation might come from the widely scattered aftershocks.
    Keywords: 550 - Earth sciences
    Language: English
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  • 10
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    Colorado Basin 3D structure and evolution, Argentine passive margin (2013)
    In:  Tectonophysics
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Language: English
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  • 11
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    Imaging fluid-related subduction processes beneath Central Java (Indonesia) using seismic attenuation tomography (2013)
    In:  Tectonophysics
    Details
    Publication Date: 2020-02-12
    Description: We use local earthquake data observed by the amphibious, temporary seismic MERAMEX array to derive spatial variations of seismic attenuation (Qp) in the crust and upper mantle beneath Central Java. The path-averaged attenuation values (t∗) of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique. These 1929 t∗-values inverted by a least-squares tomographic inversion yield the 3D distribution of the specific attenuation (Qp). Analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the Qp-model. We notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km. Most of this anomaly seems to be related to the Eocene–Miocene Kendeng Basin (mainly in the eastern part of the study area). Enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts, presence of fluids and increased temperatures in the middle to upper crust. The middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc. Enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids.
    Keywords: 550 - Earth sciences
    Language: English
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  • 12
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    RMS - Rather Meaningless Simplification? (2013)
    In:  25. Schmucker-Weidelt-Kolloquium für Elektromagnetische Tiefenforschung
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    Publication Date: 2020-02-12
    Description: For a long time the root mean square (RMS) error has been used in the EM community: - to characterize data fit for a particular model; - as a criterion to compare several models obtained from inversion. The RMS error appears to be a natural choice since we usually tackle inverse problems in a least-squares sense. Over the years, RMS became a customary criterion and gained ultimate significance. However, on the hunt for low RMS values, one often needs to introduce subjectivity by arbitrarily adjusting error floors or masking “bad” data without referring to the assumptions behind RMS. In this contribution, we revisit basic assumptions behind RMS, demonstrate its deficiency and propose alternative ways, which may provide more insight into our data and allow a more comprehensive assessment of the quality of the modelling result/resistivity model.
    Keywords: 550 - Earth sciences
    Language: English
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  • 13
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    Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz (2013)
    In:  Journal of Seismology
    Details
    Publication Date: 2020-02-12
    Description: Amplitude ratio of 30 short-period conspicuous P5KP and PKPab phases from five intermediate depth or deep events in Fiji-Tonga recorded at European stations around 150° distance shows a mean value two to three times the ratio of the synthetic amplitudes obtained by the normal-mode theory (and ak135 model) or by full-wave theory (and PREM). There is a large variance in the results, also observed in five amplitude ratios from one event in Argentina observed at temporary stations in China around 156°. Global recordings of three major deep earthquakes in Fiji, Bonin, and Western Brazil observed at ASAR, WRA, and ZRNK arrays, at 59 North America stations and at six South Pole stations displayed conspicuous P4KP and PcP (or ScP) phases. The amplitude ratio values of P4KP vs P(S)cP are sometimes almost one order of magnitude larger than the corresponding values of the synthetics. In both cases, arrival times and slowness values (corrected for ellipticity and station elevation) at the distances up to 23° beyond the A cutoff point predicted by ray theory match both the synthetics, suggesting the observations are the AB branch of PmKP (m = 4, 5) around 1 Hz. In disagreement to ray theory, no reliable BC branch is observed neither on the recordings nor on the normal-mode synthetics. The high amplitude ratio values cannot be explained by realistic perturbations of the velocity or attenuation values of the global models in the proximity of the core-to-mantle boundary (CMB). We speculate that the focusing effects and/or strong scattering most likely associated to some anomalous velocity areas of the lowermost mantle are responsible for that. The results suggest limitations of the previous evaluations of the short-period attenuation in the outer core from PmKP amplitudes (m ≥ 3), irrespective of the fact that they are obtained by using ray theory, normal-mode or full-wave synthetics. Attempts to use PmKP arrival times in order to refine velocity structure in the proximity of CMB should be also regarded with care if the propagation times have been computed with ray theory.
    Keywords: 550 - Earth sciences
    Language: English
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  • 14
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    Ambient-noise tomography of north Tibet limits geological terrane signature to upper-middle crust (2013)
    In:  Geophysical Research Letters
    Details
    Publication Date: 2020-02-12
    Description: The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere–asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are non-volcanic tremors, although the origin of these tremor-type events is not clear.
    Keywords: 550 - Earth sciences
    Language: English
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  • 15
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    Teleseismic tomography of the southern Puna plateau in Argentina and adjacent regions (2013)
    In:  Tectonophysics
    Details
    Publication Date: 2020-02-12
    Description: We performed a teleseismic P wave tomography study using seismic events at both teleseismic and regional distances, recorded by a temporary seismic array in the Argentine Puna Plateau and adjacent regions. The tomographic images show the presence of a number of positive and negative anomalies in a depth range of 20–300 km beneath the array. The most prominent of these anomalies corresponds to a low-velocity body, located in the crust, most clearly seen in the center of the array (27°S, 67°W) between the Cerro Peinado volcano, the Cerro Blanco caldera and the Farallon Negro in the east. This anomaly (southern Puna Magmatic Body) extends from the northern most part of the array and follows the line with the highest density of stations towards the south where it becomes smaller. It is flanked by high velocities on the west and the east respectively. On the west, the high velocities might be related to the subducted Nazca plate. On the northeast the high velocity block coincides with the position of the Hombre Muerto basin in the crust and could be indicating an area of lithospheric delamination where we detected a high velocity block at 100 km depth on the eastern border of the Puna plateau, north of Galan. This block might be related to a delamination event in an area with a thick crust of Paleozoic metamorphic rocks at the border between Puna and Eastern Cordillera. In the center of the array the Southern Puna magmatic body is also flanked by high velocities but the most prominent region is located on the east and is interpreted as part of the Sierras Pampeanas lithosphere with high velocities. The position of the Sierras Pampeanas geological province is key in this area as it appears to limit the extension of the plateau towards the south.
    Keywords: 550 - Earth sciences
    Language: English
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  • 16
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    The lithosphere-asthenosphere boundary in the eastern part of the Dead Sea Basin (DSB) from S-to-P receiver functions (2013)
    In:  Arabian Journal of Geosciences
    Details
    Publication Date: 2020-02-12
    Description: Clear S-to-P converted waves from the crust–mantle boundary (Moho) and lithosphere–asthenosphere boundary (LAB) have been observed on the eastern part of the Dead Sea Basin (DSB), and are used for the determination of the depth of the Moho and the LAB. A temporary network consisting of 18 seismic broad-band stations was operated in the DSB region as part of the DEad Sea Integrated REsearch project for 1.5 years beginning in September 2006. The obtained Moho depth (∼35 km) from S-to-P receiver functions agrees well with the results from P-to-S receiver functions and other geophysical data. The thickness of the lithosphere on the eastern part of the DSB is about 75 km. The results obtained here support and confirm previous studies, based on xenolith data, geodynamic modeling, heat flow observations, and S-to-P receiver functions. Therefore, the lithosphere on the eastern part of the DSB and along Wadi Araba has been thinned in the Late Cenozoic, following rifting and spreading of the Red Sea. The thinning of the lithosphere occurred without a concomitant change in the crustal thickness and thus an upwelling of the asthenosphere in the study area is invoked as the cause of the lithosphere thinning.
    Keywords: 550 - Earth sciences
    Language: English
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  • 17
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    Discrimination of induced seismicity by full moment tensor inversion and decomposition (2013)
    In:  Journal of Seismology
    Details
    Publication Date: 2020-02-12
    Description: Human activities, including operations related to mining and reservoir exploitation, may induce seismicity and pose a risk for population and infrastructures. While different observations are commonly used to assess the origin of earthquakes, there is a lack of rules and methods for the discrimination between natural and induced seismicity. The inversion and decomposition of the full moment tensor and the observation of relevant deviation from a pure double couple (DC) model may be an indicator for induced seismicity. We establish here a common procedure to analyse a set of natural and induced events of similar magnitude, which occurred in Germany and neighbouring regions. The procedure is based on an inversion method and on a consistent velocity model and recording network. Induced seismicity is recorded during different mining and/or reservoir exploitations. Moment tensors are inverted using a multi-step inversion approach. This method, which was successfully applied in previous studies at regional and teleseismic distances, is further developed here to account for full moment tensor analysis. We first find a best DC solution and then perform a full moment tensor inversion, fitting full waveforms amplitude spectra at regional distances. The moment tensor solution is decomposed into DC, compensated linear vector dipole and isotropic terms. The discrimination problem is then investigated through the evaluation of distributions of non-DC source components for natural and induced data sets. Results illustrate the potential of the inversion and discrimination approach. Additional detailed analyses are carried out for the two most significant induced earthquakes, and rupture models are compared with the full moment tensor solutions.
    Keywords: 550 - Earth sciences
    Language: English
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  • 18
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    The 2011 Mw 9.0 Tohoku Earthquake: Comparison of GPS and Strong‐Motion Data (2013)
    In:  Bulletin of the Seismological Society of America
    Details
    Publication Date: 2020-02-12
    Description: Near‐field ground‐motion data are available in semi‐real time either from modern strong‐motion or continuous Global Positioning System (GPS) networks, allowing robust solutions for earthquake source parameters, which are useful for rapid disaster assessment and early warning. These wide applications require the ground‐motion data to cover a very broad frequency band that, however, is usually not available. This paper presents a case study on the 2011 Mw 9.0 Tohoku earthquake, showing how the ground‐motion information from geodetic and seismic instrumentations is complementary, and suggesting the joint use of both types of data, particularly when the network coverage is sparse. First the strong‐motion records from the two Japanese networks, K‐NET and KiK‐Net, are analyzed using an automatic empirical baseline correction tool. The static coseismic displacement data are obtained by double integration and then used to derive the permanent slip distribution on the earthquake fault. Comparisons with the corresponding GPS‐based solutions yield a quantitative estimation of uncertainties of the empirical baseline correction. Furthermore, a dozen nearby GPS and strong‐motion station pairs are selected to demonstrate that the information in their time series agrees with each other. Finally, methods for combining both types of ground‐motion observation systems are discussed, and the wide applicability of this approach is highlighted.
    Keywords: 550 - Earth sciences
    Language: English
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    S-wave velocity images of the Dead Sea Basin provided by ambient seismic noise (2013)
    In:  Journal of Asian Earth Sciences
    Details
    Publication Date: 2020-02-12
    Description: Based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small-scale array, we have obtained shear wave velocity images of the uppermost materials that make up the Dead Sea Basin. We extracted empirical Green’s functions from cross-correlations of long-term recordings of continuous data, and measured inter-station Rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0.1–0.5 Hz bandwidth. A tomographic inversion of the travel times estimated for each frequency is performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved. Subsequently, the velocity-frequency curves are inverted to obtain S-wave velocity images of the study area as horizontal depth sections and longitude- and latitude-depth sections. The results, which are consistent with other previous ones, provide clear images of the local seismic velocity structure of the basin. Low shear velocities are dominant at shallow depths above 3.5 km, but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the Lisan Peninsula. The lack of low speeds at the sampling depth of 11.5 km implies that there are no sediments and therefore that the basement is near 10–11 km depth, but gradually decreasing from south to north. The results also highlight the bowl-shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin. The structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north–south direction. Infill materials down to ∼8 km depth are observed in the hollow of the basin, unlike what happens in the north and south where they are spread beyond the western Dead Sea shore.
    Keywords: 550 - Earth sciences
    Language: English
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    Geo-electromagnetic monitoring of the Andean Subduction Zone in Northern Chile (2013)
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    Publication Date: 2020-02-12
    Description: Adapting the magnetotelluric (MT) method for monitoring the dynamic behaviour of the Andean subduction system in Northern Chile is focus of this thesis. Electromagnetic fields, sampled at nine permanent MT stations which cover an area of approximately 250 x 100 km² in the Andean fore-arc, are evaluated to monitor the electrical resistivity structure associated with the deep hydraulic system of the subduction zone. The long term monitoring of geo-electromagnetic fields reveals different types of temporal variations of vertical magnetic transfer functions (VTF) in different period ranges which are evaluated and interpreted. Computation of time series of daily VTFs of an overall length of 4 years exhibit seasonal variations with amplitudes of more than 100% of their absolute values for different components at all sites of the array. The observed seasonal variation affects almost exclusively the east-west magnetic field component for periods between 100 and 3000 seconds. These ground-based measurements of magnetic and electric fields exhibit statistically significant coherences with the interplanetary electric field (IEF) derived from solar wind and interplanetary magnetic field data of the Advanced Composition Explorer (ACE) satellite. The IEF penetrates the polar ionosphere from where it propagates towards equatorial latitudes by wave guide transmission, with ionosphere and solid Earth acting as conducting boundaries. Signal coherence between IEF and ground data peaks at periods of approximately 90 min and up to the four harmonics. Coherence values reach 0.4 at these periods and depend on the electromagnetic field component. They vary with season and local time. Transfer functions computed between IEF and ground-based electric and magnetic fields show local maxima at similar periods (90 min and harmonics). The coupling between the east-west magnetic field component and the IEF shows significant seasonal variability, much larger than for the other electromagnetic field components. We conclude that the IEF drives primarily a global circuit of Pedersen currents in the ionosphere. Resulting time-varying magnetic fields induce electric currents in the ground. Related ground-based magnetic (primarily north-south) and electric (primarily east-west) signals vary coherently at all local times and seasons. Conversely, magnetic signals caused by the IEF-driven Hall currents depend much on local time and season. We show for the first time that these ionospheric Hall currents cause no induction in the ground, but they generate magnetic signatures that are confined to the waveguide between ionosphere and Earth's surface. Geo-electromagnetic depth sounding applications as MT assume both spatial and temporal uniform external electromagnetic source fields. The seasonal variation of VTFs exhibits a systematic violation of this basic assumption in Northern Chile. The consequence is a systematic seasonal rotation and length variation of the induction arrows of the period band between 100 and 3000 seconds. If not taken into account, the structure of an electrical resistivity model of the subsurface, obtained by MT inversion, would be distorted. Removing this source field effect with a low-pass filter allows evaluation of residual variations of the VTF time-series which last longer than one year. During 2008 and 2009, I observe a significant variation of the VTFs in the southern part of the network for periods between 1500 and 4000 seconds. To simulate this variation, a 3D reference resistivity model is obtained by inversion of MT and VTF data using eight stations of the network. A region of high conductivity matches spatially with the hydrated mantle wedge. By trial and error, the 3D reference image of the deep electrical resistivity structure is modified and 3D forward modelling is applied to explain temporal variations in the VTFs similar to our observations. That requires modification of the electrical resistivity structure in a region which coincides roughly with the plate interface directly down-dip of the Mw7.7 2007 Tocopilla earthquake. We speculate that the anomalous temporal variations of the VTFs may be caused by large scale fluid relocation in the aftermath of the seismic event.
    Keywords: 550 - Earth sciences
    Language: English
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    Scandinavia: A former Tibet? (2013)
    In:  Geochemistry Geophysics Geosystems (G3)
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    Publication Date: 2020-02-12
    Description: The Himalaya and the Tibetan Plateau are uplifted by the ongoing northward underthrusting of the Indian continental lithosphere below Tibet resulting in lithospheric stacking. The layered structure of the Tibetan upper mantle is imaged by seismic methods, most detailed with the receiver function method. Tibet is considered as a place where the development of a future craton is currently under way. Here we study the upper mantle from Germany to northern Sweden with seismic S receiver functions and compare the structure below Scandinavia with that below Tibet. Below Proterozoic Scandinavia, we found two low-velocity zones on top of each other, separated by a high-velocity zone. The top of the upper low-velocity zone at about 100 km depth extends from Germany to Archaean northern Sweden. It agrees with the lithosphere-asthenosphere boundary (LAB) below Germany and Denmark. Below Sweden it is known as the 8°discontinuity, or as a mid-lithospheric discontinuity (MLD), similar to observations in North America. Seismic tomography places the LAB near 200 km in Scandinavia, which is close to the top of our deeper low-velocity zone. We also observed the bottom of the asthenosphere (the Lehmann discontinuity) deepening from 180 km in Germany to 260 km below Sweden. Remnants of old subduction in the upper about 100 km below Scandinavia and Finland are known from controlled source seismic experiments and local earthquake studies. Recent tomographic studies indicate delamination of the lithosphere below southern Scandinavia and northern Germany. We are suggesting that the large-scale layered structure in the Scandinavian upper mantle may be caused by processes similar to the ongoing lithospheric stacking in Tibet.
    Keywords: 550 - Earth sciences
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    Structure and seismogenic properties of the Mentawai segment of the Sumatra subduction zone revealed by local earthquake traveltime tomography (2012)
    In:  Journal of Geophysical Research
    Details
    Publication Date: 2020-02-12
    Description: On 12 September 2007, an Mw 8.4 earthquake occurred within the southern section of the Mentawai segment of the Sumatra subduction zone, where the subduction thrust had previously ruptured in 1833 and 1797. Traveltime data obtained from a temporary local seismic network, deployed between December 2007 and October 2008 to record the aftershocks of the 2007 event, was used to determine two-dimensional (2-D) and three-dimensional (3-D) velocity models of the Mentawai segment. The seismicity distribution reveals significant activity along the subduction interface and within two clusters in the overriding plate either side of the forearc basin. The downgoing slab is clearly distinguished by a dipping region of high Vp (8.0 km/s), which can be a traced to ∼50 km depth, with an increased Vp/Vs ratio (1.75 to 1.90) beneath the islands and the western side of the forearc basin, suggesting hydrated oceanic crust. Above the slab, a shallow continental Moho of less than 30 km depth can be inferred, suggesting that the intersection of the continental mantle with the subducting slab is much shallower than the downdip limit of the seismogenic zone despite localized serpentinization being present at the toe of the mantle wedge. The outer arc islands are characterized by low Vp (4.5–5.8 km/s) and high Vp/Vs (greater than 2.0), suggesting that they consist of fluid saturated sediments. The very low rigidity of the outer forearc contributed to the slow rupture of the Mw 7.7 Mentawai tsunami earthquake on 25 October 2010.
    Keywords: 550 - Earth sciences
    Language: English
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    Dead Sea Basin Imaged by Ambient Seismic Noise Tomography (2012)
    In:  Pure and Applied Geophysics
    Details
    Publication Date: 2020-02-12
    Description: In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests.
    Keywords: 550 - Earth sciences
    Language: English
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    Characterization of microbial activity in pockmark fields of the SW-Barents Sea (2012)
    In:  Marine Geology
    Details
    Publication Date: 2020-02-12
    Description: Multibeam bathymetry revealed the occurrence of numerous craterlike depressions, so-called pockmarks, on the sea floor of the Hammerfest Basin and the Loppa High, south-western Barents Sea. To investigate whether these pockmarks are related to ongoing gas seepage, microbial processes associated with methane metabolism were analyzed using geochemical, biogeochemical and microbiological techniques. Gravity cores were collected along transects crossing individual pockmarks, allowing a direct comparison between different locations inside (assumed activity center), on the rim, and outside of a pockmark (reference sites). Concentrations of hydrocarbons in the sediment, particularly methane, were measured as headspace (free) gas, and in the occluded and adsorbed gas fraction. Down to a depth of 2.6 m below sea floor (mbsf) sulfate reduction rates were quantified by radiotracer incubations. Concentrations of dissolved sulfate in the porewater were determined as well. Neither the sulfate profiles nor the gas measurements show any evidence of microbial activity or active fluid venting. Methane concentrations and sulfate reduction rates were extremely low or even below the detection limit. The results show that the observed sediment structures are most likely paleo-pockmarks, their formation probably occurred during the last deglaciation.
    Keywords: 550 - Earth sciences
    Language: English
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    Lithosphere structure of the NE Bohemian Massif (Sudetes) - A teleseismic receiver function study (2012)
    In:  Tectonophysics
    Details
    Publication Date: 2020-02-12
    Description: In 2004 and 2005 a passive seismic experiment was carried out in the northern and northeastern part of the Bohemian Massif (Sudetes) to study the lithospheric structure. We present results from Ps and Sp receiver function analyses. With one exception, Moho depth at stations in the northwestern part of the study area varies between 28 and 32 km. Thicker crust up to 35 km was mapped toward the south (Moldanubian unit) and toward the east (Moravo–Silesian and Brunovistulian units) confirming results from previous active seismic measurements. There exists a relatively sharp step in Moho depth between units of the central Sudetes (~ 30 km) and the Moravo–Silesian unit (~ 35 km). The vp/vs ratios inverted from primary and multiple Moho Ps conversions hint for different crustal compositions of the units. Toward the Carpathian thrust we have no clear indications for any crustal root or slab beneath the western Carpathians. However, our data suggests a deepening of the Moho or at least a complicated crust–mantle transition in this area. Additional Ps phases were observed between 6 and 10 s delay time in the Sudetes. These phases cannot be explained by Moho reverberations, but are most probably caused by low velocity zones in the middle crust or lithospheric mantle as shown by modeling of theoretical receiver functions. The stations showing these abnormal phases are located in the area of Permo-Carboniferous basins on probably Teplá–Barrandian crust. Therefore we assume that the phases hint at a mid-crustal low velocity zone between 16 and 20 km depth, which is interpreted as a felsic solidified magma reservoir of the Permo-Carboniferous volcanism beneath the Sudetic Basins. Sp receiver functions show phases with negative polarity at 9 to 12 s lead time on average, which we interpret as lithosphere–asthenosphere boundary at about 80 to 110 km depth.
    Keywords: 550 - Earth sciences
    Language: English
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    Melt infiltration of the lower lithosphere beneath the Tanzania craton and the Albertine rift inferred from S receiver functions (2012)
    In:  Geochemistry Geophysics Geosystems (G3)
    Details
    Publication Date: 2020-02-12
    Description: The transition between the lithosphere and the asthenosphere is subject to numerous contemporary studies as its nature is still poorly understood. The thickest lithosphere is associated with old cratons and platforms and it has been shown that seismic investigations may fail to image the lithosphere-asthenosphere boundary in these areas. Instead, several recent studies have proposed a mid-lithospheric discontinuity of unknown origin existing under several cratons. In this study we investigate the Tanzania craton in East Africa which is enclosed by the eastern and western branches of the East African Rift System. We present evidence from S receiver functions for two consecutive discontinuities at depths of 50–100 km and 140–200 km, which correspond to significant S wave velocity reductions under the Tanzania craton and the Albert and Edward rift segments. By comparison with synthetic waveforms we show that the lower discontinuity coincides with the LAB exhibiting velocity reductions of 6–9%. The shallower interface reveals a velocity drop that varies from 12% beneath the craton to 24% below the Albert-Edward rift. It is interpreted as an infiltration front marking the upper boundary of altered lithosphere due to ascending asthenospheric melts. This is corroborated by computing S velocity variations based on xenolith samples which exhibit a dense system of crystallized veins acting as pathways of the infiltrating melt. Mineral assemblages in these veins are rich in phlogopite and pyroxenite which can explain the reduced shear wave velocities. Melt infiltration represents a suitable mechanism to form a mid-lithospheric discontinuity within cratonic lithosphere that is underlain by anomalously hot mantle.
    Keywords: 550 - Earth sciences
    Language: English
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    High-resolution local earthquake tomography of the southern Dead Sea area. (2012)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: Local earthquake data from a dense temporary seismological network in the southern Dead Sea area have been analysed within the project DESIRE (Dead Sea Integrated Research Project). Local earthquakes are used for the first precise image of the distribution of the P-wave velocity and the vP/vS ratios. 65 stations registered 655 local events within 18 months of observation time. A subset of 530 well-locatable events with 26 730 P- and S-arrival times was used to calculate a tomographic model for the vP and vP/vS distribution. Since the study area is at first-order 2-D, a gradual approach was chosen, which compromised a 2-D inversion followed by a 3-D inversion. The sedimentary basin fill is clearly imaged through high vP/vS ratios and low vP. The basin fill shows an asymmetric structure with average depth of 7 km at the western boundary and depth between 10 and 14 km at the eastern boundary. This asymmetry is reflected by the vertical strike-slip eastern border fault, and the normal faulting at the western boundary, caused by the transtensional deformation within the last 5 Myr. Within the basin fill the Lisan salt diapir is imaged through low vP/vS ratios, reflecting its low fluid content. The extensions were determined to 12 km in E–W and 17 km in N–S direction while its depth is 5–6 km. The thickness of the pre-basin sediments below the basin fill cannot be derived from the tomography data—it is estimated to less than 3 km from former investigations. Below the basin, down to 18 km depth very low P-wave velocities and low vP/vS ratios are observed—most likely caused by fluids from the surrounding crust or the upper mantle.
    Keywords: 550 - Earth sciences
    Language: English
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    Shear velocity structure across the Sumatran Forearc-Arc (2012)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: We present a series of 1-D shear velocity models for the Sumatran Forearc and Arc derived from Rayleigh wave group dispersion in noise correlation functions from vertical and pressure records from an onshore–offshore seismic deployment. The 1-D models represent the crustal structure of the downgoing Indian Plate, the accretionary prism and the arc. There is a progression in shear velocity across the forearc to the arc associated with thickening of the accretionary prism and the development of an arc crust. The velocity structure inferred for the upper 20 km based on path averages between stations on the accretionary prism has velocities consistent with a thick sediment package in agreement with estimates of depth to the plate boundary determined from active source experiments. We also find low Indian Plate shear velocities, 〈4 km s−1 to 25 km depth beneath our station locations on the downgoing plate. These low seismic velocities are consistent with at least 14–24 per cent serpentinization of the oceanic crust and upper mantle of the downgoing plate. This high degree of serpentinization, may weaken the plate interface and explain the segmentation observed in the great Sumatran thrust earthquakes if the serpentinization is localized. The success of this study suggests that future onshore–offshore seismic deployments will be able to utilize this method.
    Keywords: 550 - Earth sciences
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    A wireless mesh sensing network for early warning (2012)
    In:  Journal of Network and Computer Applications
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    Publication Date: 2020-02-12
    Description: Earthquake early warning systems should provide reliable warnings as quickly as possible with a minimum number of false and missed alarms. Wireless meshed networks, coupled with low-cost seismometers for monitoring, evaluation, and information about seismic vibrations in space and time are introducing a new generation of warning infrastructures for mega-cities. The use of a cooperative method for signal analysis makes it possible to distinguish earthquakes (with a certain minimal magnitude) from other ground shaking in a city. The paper gives a short overview of our approach for developing decentralized early warning systems and an evaluation based on experiences gained from model investigations, testbeds in Berlin, and prototype installations in Istanbul.
    Keywords: 550 - Earth sciences
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    A complex linear least-squares method to derive relative and absolute orientations of seismic sensors (2012)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: Determining the relative orientation of the horizontal components of seismic sensors is a common problem that limits data analysis and interpretation for several acquisition setups, including linear arrays of geophones deployed in borehole installations or ocean bottom seismometers deployed at the seafloor. To solve this problem we propose a new inversion method based on a complex linear algebra approach. Relative orientation angles are retrieved by minimizing, in a least-squares sense, the l2-norm between the complex traces (hodograms) of adjacent pairs of sensors. This methodology can be applied without restrictions only if the wavefield recorded by each pair of sensors is very similar. In most cases, it is possible to satisfy this condition by low-pass filtering the recorded waveforms. The main advantage of our methodology is that, in the complex domain, the relative orientations of seismic sensors can be viewed as a linear inverse problem, which ensures that the preferred solution corresponds to the global minimum of a misfit function. It is also possible to use simultaneously more than one independent data set (other seismic events) to better constrain the solution of the inverse problem. Furthermore, by a computational point of view, our method results faster than the relative orientation methods based on waveform cross-correlation. After several tests on synthetic data sets we applied successfully our methodology to different types of real data. These applications include the alignment of borehole sensors relative to a Vertical Seismic Profiling (VSP) acquisition and the orientation of Ocean Bottom Seismometers (OBS) relative to a neighbouring land station of known orientation. Using land stations, the absolute orientation of OBS can be retrieved. Finally, as a last application, we checked the correct orientation for land stations of a seismological array in Germany.
    Keywords: 550 - Earth sciences
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    Microseimicity distribution in the southern Dead Sea area and its implications on the structure of the basin (2012)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: While the Dead Sea basin has been studied for a long time, the available knowledge about the detailed seismicity distribution in the area, as well as the deeper structure of the basin, is limited. Therefore, within the framework of the international project DESIRE (DEad Sea Integrated REsearch project), a dense temporary local seismological network was operated in the southern Dead Sea area. We use 530 local earthquakes, having all together 26 730 P- and S-arrival times for a simultaneous inversion of 1-D velocity models, station corrections and precise earthquake locations. Jackknife tests suggest an accuracy of the derived hypocentre locations of about 1 km. Thus, the result is the first clear image of the absolute distribution of the microseismicity of the area, especially in depth. The seismicity is concentrated in the upper crust down to 20 km depth while the lower limit of the seismicity is reached at 31 km depth. The seismic events at the eastern boundary fault (EBF) in the southern part of the study area represent the northward transform motion of the Arabian Plate along the Dead Sea Transform. North of the Boqeq fault the seismic activity represents the transfer of the motion in the pull-apart basin from the eastern to the western boundary. We find that from the surface downward the seismic events are tracing the boundary faults of the basin. The western boundary is mapped down to 12 km depth while the EBF reaches about 17 km depth, forming an asymmetric basin. One fifth of the data set is related to a specific cluster in time and space, which occurred in 2007 February at the western border fault. This cluster is aligned vertically, that is, it is perpendicular to the direction of the dominating left-lateral strike-slip movement at the main transform fault.
    Keywords: 550 - Earth sciences
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    Fast Kinematic Waveform Inversion and Robustness Analysis: Application to the 2007 Mw 5.9 Horseshoe Abyssal Plain Earthquake Offshore Southwest Iberia (2012)
    In:  Bulletin of the Seismological Society of America
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Toward understanding tectonic control on the Mw 8.8 2010 Maule Chile earthquake (2012)
    In:  Earth and Planetary Science Letters
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    Publication Date: 2020-02-12
    Description: The Maule earthquake of 27th February 2010 (Mw=8.8) affected ~500 km of the Nazca-South America plate boundary in south-central Chile producing spectacular crustal deformation. Here, we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous GPS, both in near- and farfield regions. Earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published GPS, InSAR, and land-level changes data using Green's functions generated by a spherical finite-element model with realistic subduction zone geometry. The combination of the data sets provided a good resolution, indicating that most of the slip was well resolved. Coseismic slip was concentrated north of the epicenter with up to 16 m of slip, whereas to the south it reached over 10m within two minor patches. A comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap. Slip deficit distribution shows an apparent local overshoot that highlight cycle-to-cycle variability,which has to be taken into accountwhen anticipating future events from interseismic observations. Rupture propagation was obviously not affected by bathymetric features of the incoming plate. Instead, splay faults in the upper plate seem to have limited rupture propagation in the updip and along-strike directions. Additionally, we found that along-strike gradients in slip are spatially correlated with geometrical inflections of the megathrust. Our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts.
    Keywords: 550 - Earth sciences
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    Direct penetration of the interplanetary electric field to low geomagnetic latitudes and its effect on magnetotelluric sounding (2012)
    In:  Journal of Geophysical Research
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    Publication Date: 2020-02-12
    Description: [1] Long-term monitoring of geoelectromagnetic fields, recorded with a network of nine stations covering an area of approximately 25,000 km2at low geomagnetic latitudes in northern Chile, reveals systematic and seasonally modulated variations of geomagnetic field properties. The observed seasonal variation affects almost exclusively the east-west magnetic field component for periods between 100 and 3000 s. The ground-based measurements of magnetic and electric fields show statistically significant coherences with the interplanetary electric field derived from solar wind and interplanetary magnetic field data of the Advanced Composition Explorer satellite. The interplanetary electric field (IEF) penetrates the polar ionosphere from where it propagates toward equatorial latitudes by waveguide transmission, with ionosphere and solid Earth acting as conducting boundaries. Signal coherence between IEF and ground data peaks at periods of approximately 90 min and up to the four harmonics. Coherence values reach 0.4 at these periods and depend on the electromagnetic field component. They vary with season and local time. Transfer functions computed between IEF and ground-based electric and magnetic fields show local maxima at similar periods (90 min and harmonics). The coupling between the east-west magnetic field component and the IEF shows significant seasonal variability, much larger than the other electromagnetic field components. We conclude that the IEF drives primarily a global circuit of Pedersen currents in the ionosphere. Resulting time-varying magnetic fields induce electric currents in the ground. Related ground-based magnetic (primarily north-south) and electric (primarily east-west) signals vary coherently at all local times and seasons. Conversely, magnetic signals caused by the IEF-driven Hall currents depend much on local time and season. We show for the first time that these ionospheric Hall currents cause no induction in the ground, but they generate magnetic signatures that are confined to the waveguide between ionosphere and Earth's surface.
    Keywords: 550 - Earth sciences
    Language: English
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    Splay fault slip during the Mw 8.8 2010 Maule Chile earthquake (2012)
    In:  Geology
    Details
    Publication Date: 2020-02-12
    Description: Splay faults are thrusts that emerge from the plate boundaries of subduction zones. Such structures have been mapped at several convergent margins and their activity commonly ascribed to large megathrust earthquakes. However, the behavior of splay faults during the earthquake cycle is poorly constrained because typically these structures are located offshore and are difficult to access. Here we use geologic mapping combined with space and land geodesy, as well as offshore sonar data, to document surface-fault ruptures and coastal uplift at Isla Santa María in south-central Chile (37°S) caused by the 27 February 2010 Maule earthquake (Mw 8.8). During the earthquake, the island was tilted parallel to the margin, and normal faults ruptured the surface and adjacent ocean bottom. We associate tilt and crestal normal faulting with growth of an anticline above a blind reverse fault rooted in the Nazca–South America plate boundary, which slipped during the Maule earthquake. The splay fault system has formed in an area of reduced coseismic plate-boundary slip, suggesting that anelastic deformation in the upper plate may have restrained the 2010 megathrust rupture. Surface fault breaks were accompanied by prominent discharge of fluids. Our field observations support the notion that splay faulting may frequently complement and influence the rupture of subduction-zone earthquakes.
    Keywords: 550 - Earth sciences
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    Strain accumulation controls failure of a plate boundary zone: Linking deformation of the Central Andes and lithosphere mechanics (2012)
    In:  Geochemistry Geophysics Geosystems (G3)
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Tracking unilateral earthquake rupture by P-wave polarization analysis (2012)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: Rapid estimation of earthquake rupture propagation is essential to declare an early warning for tsunami-generating earthquakes. An increasing number of seismological methods have been developed to determine rupture parameters, such as length, velocity and propagation direction, especially since the occurrence of the Sumatra–Andaman earthquake that resulted in a devastating tsunami in the Indian Ocean region. Here, we present a new method to follow the rupture process in near real time by a polarization analysis of local and regional P phases that permits a faster determination of rupture properties than using teleseismic records. The new technique has the capability to provide detailed information in less than 10 min. Originally, the method stems from a single-station earthquake location method and is expanded here to monitor P-phase polarization variations through time. As the earthquake source moves away from the hypocentre, the backazimuth of an incoming P phase is expected to change accordingly. With polarization analysis we may be able to monitor the temporal change in Pwave backazimuth to follow the rupture process in near real time. Three component P phases are scanned to determine the azimuthal variation as a function of time. The backazimuth of a moving rupture front is determined by the first eigenvector of the covariance matrix. The linearity of the particle motion is used as a measure of the quality of the data. Seismic stations at local and regional distances (〉∼ 30◦) are used. We tested the new method with a theoretical simulation and observed seismograms of the Sumatra–Andaman earthquake (2004 December 26, Mw = 9.3), and we were able to follow the rupture for the first 200 s. For larger ruptures, stations at more than 30◦ epicentral distances would be required. The method is also successfully applied to the Wenchuan earthquake (2008 May 12, Mw = 8.0).
    Keywords: 550 - Earth sciences
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    Lithium Isotope Variations in Ocean Island Basalts - Implications for the Development of Mantle Heterogeneity (2012)
    In:  Journal of Petrology
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    Publication Date: 2020-02-12
    Description: Lithium elemental and isotopic compositions of 33 glass and whole-rock samples from nine oceanic island regions were determined to characterize the Li inventory of the deep mantle. The Li contents of the investigated lavas range from 1·5 to 13·3 μg g−1, whereas δ7Li ranges from 2·4 to 4·8‰. There are weak co-variations between the Li/Y, δ7Li, and Sr–Nd–Pb isotope compositions of the lavas, indicating that the Li elemental and isotopic characteristics of ocean island basalt to some extent reflect mantle source heterogeneity. In detail, HIMU-type lavas are characterized by δ7Li values (up to 4·8‰) slightly heavier than those for average normal mid-ocean ridge basalt (3·4 ± 1·4‰) and by comparatively low Li contents; EM1-type lavas are characterized by isotopically light Li (average 3·2‰) and relative Li enrichment, whereas EM2-type lavas tend to heavier δ7Li values (up to 4·4‰) with high Li concentrations. The Li contents and isotope characteristics of HIMU-type lavas are consistent with recycling of altered and dehydrated oceanic crust, whereas those of the EM1-type lavas can be attributed to sediment recycling. The Li characteristics of EM2-type lavas may reflect reworking of mantle wedge material that has been infiltrated by fluids derived from the subducting plate.
    Keywords: 550 - Earth sciences
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    Response of forearc crustal faults to the megathrust earthquake cycle: InSAR evidence from Mejillones Peninsula, Northern Chile. (2012)
    In:  Earth and Planetary Science Letters
    Details
    Publication Date: 2020-02-12
    Description: We report on a rare example of aseismic response of a creeping fault to the earthquake cycle of a nearby megathrust. Interferometric synthetic aperture radar (InSAR) is used to detect and analyze shallow creep of two crustal faults at Mejilones Peninsula, Northern Chile, located in the hanging wall of the 2007 Mw 7.7 Tocopilla subduction earthquake. We generate two independent time series of surface deformation spanning ∼3.5 yr of late interseismic and ∼1.5 yr early postseismic deformation associated with this event. The analysis reveals creep on the Mejillones fault as well as on a previously unmapped fault to the west of the Mejillones fault. The InSAR deformation maps and distributed slip models obtained from the data reveal that fault creep reversed between the interseismic and postseismic periods. Given the regional stress field perturbations due to interseismic and coseismic deformation, we argue that the observed shallow creep and its slip reversal are directly linked to the megathrust seismic cycle. Moreover, from similar eastward dips but opposite slip directions of the two faults, we infer that fault strength must be very low and that the kinematics is controlled by crustal flexure associated with the seismic cycle on the underlying megathrust. ⺠New evidence of crustal fault creep in Northern Chile from InSAR. ⺠New evidence that sense of fault creep is governed by megathrust earthquake cycles. ⺠New evidence that stress induced by megathrust earthquake alters the sense of creep.
    Keywords: 550 - Earth sciences
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    The structure of the Sumatran Fault revealed by local seismicity (2012)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Description: The combination of the Sunda megathrust and the (strike-slip) Sumatran Fault (SF) represents a type example of slip-partitioning. However, superimposed on the SF are geometrical irregularities that disrupt the local strain field. The largest such feature is in central Sumatra where the SF splits into two fault strands up to 35 km apart. A dense local network was installed along a 350 km section around this bifurcation, registering 1016 crustal events between April 2008 and February 2009. 528 of these events, with magnitudes between 1.1 and 6.0, were located using the double-difference relative location method. These relative hypocentre locations reveal several new features about the crustal structure of the SF. Northwest and southeast of the bifurcation, where the SF has only one fault strand, seismicity is strongly focused below the surface trace, indicating a vertical fault that is seismogenic to ~15 km depth. By contrast intense seismicity is observed within the bifurcation, displaying streaks in plan and cross-section that indicate a complex system of faults bisecting the bifurcation. In combination with analysis of topography and focal mechanisms, we propose that the bifurcation is a strike-slip duplex system with complex faulting between the two main fault branches.
    Keywords: 550 - Earth sciences
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    The 2007 M7.7 Tocopilla northern Chile earthquake sequence: Implications for along-strike and downdip rupture segmentation and megathrust frictional behavior (2012)
    In:  Journal of Geophysical Research
    Details
    Publication Date: 2020-02-12
    Description: In 2007 a M7.7 earthquake occurred near the town of Tocopilla within the northern Chile seismic gap. Mainshock slip, derived from coseismic surface deformation, was confined to the depth range between 30-55 km. We relocated ~1100 events during six months before and one week after the mainshock. Aftershock seismicity is first congruent to the mainshock slip and then it spreads offshore west and northwest of Mejillones Peninsula (MP). Waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the mainshock. However, a few events appear to occur in the upper plate, some with extensional mechanisms. Juxtaposing the Tocopilla aftershocks with those following the neighboring 1995 Antofagasta earthquake produces a striking symmetry across an EW axis in the center of MP. Events seem to skirt around MP, probably due to a shallower Moho there. We suggest that the seismogenic coupling zone in northern Chile changes its frictional behavior in the down-dip direction from unstable to mostly conditionally stable. For both earthquake sequences, aftershocks agglomerate in the conditionally stable region, whereas maximum inter-seismic slip deficit and co-seismic slip occurs in the unstable region. The boundary between the unstable and conditionally stable zones parallels the coastline. We identify a similar segmentation for other earthquakes in Chile and Peru, where the offshore segments break in great M〉8 earthquakes, and the onshore segments in smaller M〈8 earthquakes. Using critical taper analysis, we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate-dependency of friction.
    Keywords: 550 - Earth sciences
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    High-resolution image of the geometry and thickness of the subducting Nazca lithosphere beneath northern Chile (2011)
    In:  Journal of Geophysical Research
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    Publication Date: 2020-02-12
    Description: Results obtained from S and P receiver functions produced a clear image of the top and bottom of the subducting Nazca lithosphere beneath northern Chile. Using data from the teleseismic events recorded at 15 permanent Integrated Plate Boundary Observatory Chile (IPOC) stations, we obtained new constraints on the geometry and thickness of the descending Nazca lithosphere. We observed the subducted crust of the Nazca plate at depths ranging from 50 km beneath the Coastal Cordillera down to 110 km beneath the Western Cordillera. We found significant along‐strike variations in the geometry of the Nazca plate beneath northern Chile. On closer inspection, it appears that the oceanic Nazca plate is divided into two distinct segments as it descends beneath the continental South American plate. The transition from the relatively steeper (∼23°) and deeper slab to the north of 21°S to the flatter southern segment (∼19°) is shown reasonably clearly by our data. This feature could well be associated with variations in the curvature of the plate margin and the geometry of the Chile trench, which is mainly curved to the north of 21°S. We have also mapped the continental Moho of the South American plate at depths ranging between 60 and 70 km to the east of the Longitudinal Valley. Beneath the Coastal Cordillera, this boundary becomes invisible, probably due to the serpentinization of the forearc mantle wedge that reduces the velocity in the uppermost mantle. The base of the subducted Nazca plate was clearly identified as a sharp boundary in the results obtained from the P and S receiver functions. The thickness of the subducted oceanic Nazca plate, which has an age of ∼50 My, is estimated to be ∼50 km. Although this thickness is consistent with that predicted by thermal gradients, the explanation of the sharpness of the lithosphere‐asthenosphere boundary may require another mechanism such as hydration or melting.
    Keywords: 550 - Earth sciences
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    Rapid directivity detection by azimuthal spectra inversion (2011)
    In:  Journal of Seismology
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    Publication Date: 2020-02-12
    Description: An early detection of the presence of rupture directivity plays a major role in the correct estimation of ground motions and risks associated to the earthquake occurrence. We present here a simple method for a fast detection of rupture directivity, which may be additionally used to discriminate fault and auxiliary planes and have first estimations of important kinematic source parameters, such as rupture length and rupture time. Our method is based on the inversion of amplitude spectra from P-wave seismograms to derive the apparent duration at each station and on the successive modelling of its azimuthal behaviour. Synthetic waveforms are built assuming a spatial point source approximation, and the finite apparent duration of the spatial point source is interpreted in terms of rupture directivity. Since synthetic seismograms for a point source are calculated very quickly, the presence of directivity may be detected within few seconds, once a focal mechanism has been derived. The method is here first tested using synthetic datasets, both for linear and planar sources, and then successfully applied to recent Mw 6.2–6.8 shallow earthquakes in Peloponnese, Greece. The method is suitable for automated application and may be used to improve kinematic waveform modelling approaches.
    Keywords: 550 - Earth sciences
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    Rupture process of the 7 May 2001 Mw 4.2 Ekofisk induced earthquake (2011)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: On 2001 May 7, following unintentional water injection, a moderate size induced earthquake struck the Ekofisk oil field, North Sea. Despite of its relatively moderate magnitude, clear low-frequency waveforms could be recorded up to more than 2000 km epicentral distance, suggesting a slow rupture at very shallow depth and wave propagation through low-velocity shallow structures. The event poses a rare opportunity to constrain rupture velocity, duration and rise time of a superficial M 〉 4 event occurring on a horizontal plane in soft, water-saturated sediments. Two previous studies discussed the earthquake point source finding vertical dip-slip focal mechanisms with opposite senses of P and T axes. A further investigation was thus required to provide a basis for a deeper discussion of the failure dynamics. We significantly improve the used data set, test different earth models and derive a point source as well as a kinematic rupture model. We carefully discuss parameter uncertainties and effects related to shallow sources and wave propagation through different crustal structures to resolve the previous controversy. We additionally provide a kinematic rupture model, based on apparent source times derived from Rayleigh and Love waves. The waveforms resolve a predominant unilateral rupture along a horizontal plane at about 2 km depth. We derive an unusually slow rupture, consequence of a slow rupture velocity of about 500 m s –1 and a long rise time of about 7 s. An independent modelling of GPS- based static displacements allows to confirm the focal mechanism polarity and to locate the centroid at the eastern side of the field, resulting in a much larger seismic moment in comparison with dynamic seismic moment. The rupture directivity is confirmed by the relative location of the centroid with respect to the epicentre, which is set at the site of water injection.
    Keywords: 550 - Earth sciences
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    Crustal structure of the Dead Sea Basin (DSB) from a Receiver Function Analysis (2011)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: The Dead Sea Transform (DST) is a major left-lateral strike-slip fault that accommodates the relative motion between the African and Arabian plates, connecting a region of extension in the Red Sea to the Taurus collision zone in Turkey over a length of about 1100 km. The Dead Sea Basin (DSB) is one of the largest basins along the DST. The DSB is a morphotectonic depression along the DST, divided into a northern and a southern sub-basin, separated by the Lisan salt diapir. We report on a receiver function study of the crust within the multidisciplinary geophysical project, DEad Sea Integrated REsearch (DESIRE), to study the crustal structure of the DSB. A temporary seismic network was operated on both sides of the DSB between 2006 October and 2008 April. The aperture of the network is approximately 60 km in the E—W direction crossing the DSB on the Lisan peninsula and about 100 km in the N—S direction. Analysis of receiver functions from the DESIRE temporary network indicates that Moho depths vary between 30 and 38 km beneath the area. These Moho depth estimates are consistent with results of near-vertical incidence and wide-angle controlled-source techniques. Receiver functions reveal an additional discontinuity in the lower crust, but only in the DSB and west of it. This leads to the conclusion that the internal crustal structure east and west of the DSB is different at the present-day. However, if the 107 km left-lateral movement along the DST is taken into account, then the region beneath the DESIRE array where no lower crustal discontinuity is observed would have lain about 18 Ma ago immediately adjacent to the region under the previous DESERT array west of the DST where no lower crustal discontinuity is recognized.
    Keywords: 550 - Earth sciences
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    Receiver function images of the base of the lithosphere in the Alboran Sea region (2011)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: We analyse data from seismic stations surrounding the Alboran Sea between Spain and North Africa to constrain variations of the lithosphere–asthenosphere boundary (LAB) in the region. The technique used is the receiver function technique, which uses S-to-P converted teleseismic waves at the LAB below the seismic stations. We confirm previous data suggesting a shallow (60–90 km) LAB beneath the Iberian Peninsula and we observe a similarly shallow LAB beneath the Alboran Sea where the lithosphere becomes progressively thinner towards the east. A deeper LAB (90–100 km) is observed beneath the Betics, the south of Portugal and Morocco. The structure of the LAB in the entire region does not seem to show any indication of subduction related features. We also observe good P receiver function signals from the seismic discontinuities at 410 and 660 km depth which do not indicate any upper-mantle anomaly beneath the entire region. This is in agreement with the sparse seismic activity in the mantle transition zone suggesting the presence of only weak and regionally confined anomalies.
    Keywords: 550 - Earth sciences
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    Improved modeling of sea level patterns by incorporating self-attraction and loading (2011)
    In:  Journal of Geophysical Research
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    Publication Date: 2020-02-12
    Description: We implement the effects of gravitational self-attraction and loading (SAL) into a global baroclinic ocean circulation model and investigate effects on sea level patterns, ocean circulation, and density distributions. We compute SAL modifications as an additional force on the water masses at every time step by decomposing the field of ocean bottom pressure anomalies into spherical harmonic functions and then applying Love numbers to account for the elastic properties of the solid Earth. Considering SAL in the postprocessing turns out to be insufficient, especially in coastal waters and on subweekly time scales, where SAL modifies local sea level by around 0.6–0.8 cm on average; in the open ocean, changes mostly remain around 0.3 cm. Modifications of water velocities as well as of heat and salt distributions are modeled, yet they are small. Simple parameterizations of SAL effects currently used in a number of ocean circulation models suffer from the process's inhomogeneity in space and time. These parameterizations improve the modeled sea level patterns but fail to reproduce SAL impacts on circulation and density distributions. We therefore suggest to explicitly consider the full SAL effect in ocean circulation models, especially when investigating sea level variations faster than around 4 days.
    Keywords: 550 - Earth sciences
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    Landslides in Southern Kyrgyzstan: Understanding Tectonic Controls (2011)
    In:  Eos, Transactions American Geophysical Union
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    Publication Date: 2020-02-12
    Description: Frequent landsliding is one of the greatest natural hazards facing the inhabitants of Central Asia's Fergana Basin and the surrounding mountain ranges. Active tectonics in the region is rapidly building the Tien Shan, one of the highest mountain ranges on Earth, and the extreme topographic relief promotes frequent landslide activity, which causes major losses of life and property. In southwestern Kyrgyzstan alone, on average 10 people die and seven houses are destroyed each year in these sudden and rapidly moving landslides.
    Keywords: 550 - Earth sciences
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    Hengill geothermal volcanic complex (Iceland) characterized by integrated geophysical observations (2011)
    In:  Geothermics
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    Publication Date: 2020-02-12
    Description: Structural features of volcanic and hydrothermal systems can be used to infer the location of magma chambers or productive geothermal areas. The Hengill volcanic triple-junction complex has a well-developed geothermal system, which is being exploited to extract hot fluids that are used for electrical power and heat production. In the framework of the I-GET project, a 4-month temporary seismological network including seven high-dynamic broadband instruments was deployed and 1D transient electromagnetic soundings (TEM) and 3D magnetotelluric (MT) surveys were performed to improve the understanding of the relationships between structural features, seismic activity and fluid production at the Hengill geothermal system. The MT and TEM data set are analysed elsewhere. The analysis of the seismological data set allowed the detection and classification of more than 600 earthquakes, among which long-period (LP) earthquakes were observed for the first time in this area. This work focuses first on a joint inversion for the 3D velocity structure and determination of the locations of the hypocentres from about 250 local volcano-tectonic earthquakes with clear P- and S-wave arrival times. The results confirm those from earlier tomography studies in this area. Integrating the seismic velocity and resistivity models in a semi-quantitative approach by cross-plotting the resistivity model with the velocity ratio VP/VS delineates a structural body with a high seismic velocity ratio and low resistivity that is interpreted as the main heat source of the geothermal system.
    Keywords: 550 - Earth sciences
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    Short-scale variations of shear-wave splitting across the Dead Sea basin: Evidence for the offects of sedimentary fill (2011)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Description: We examine shear-wave splitting of SKS waveforms collected by a temporary array of 68 stations in the region of the Dead Sea basin. The observed splitting parameters exhibit systematic variations along a dense, EW-trending 60 km profile across the basin. The delay times vary significantly between 1.0 and 2.8 seconds with smaller values in the very center of the profile. The fast polarizations are oriented more-or-less parallel to the strike of the Dead Sea transform fault and vary between −10 and 20 degrees with respect to North. Finite-frequency waveform modeling reveals that the source-region of the small-scale lateral variations is likely located within the crust. The modeling further shows that purely isotropic velocity variations affect shear-wave splitting: To a large degree, the observed variations of splitting parameters can be explained by the sedimentary fill of the basin and its low isotropic seismic velocities, whereas the mantle is uniformly anisotropic. Our study indicates that precaution must be taken when interpreting short-scale lateral variations of shear wave splitting in terms of anisotropic structures in the crust or upper mantle.
    Keywords: 550 - Earth sciences
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    Body wave observations from cross-correlations of ambient seismic noise: A case study from the Karoo, RSA (2011)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Description: In the past decade the analysis of seismic noise has become an efficient tool to recover the Green's function between pairs of receivers by cross-correlation of seismic traces. Most studies focus on the investigation of the surface wave component of the ambient noise. Several attempts to recover the body wave part of the Green's function have been documented. In this paper I present the results of cross-correlation of seismic noise and the retrieval of refracted and reflected P-waves along a seismic line in the Karoo region (Republic of South Africa). Body wave refractions (direct phases) and reflections have been observed in the Green's functions derived from ambient noise records of up to 60 hours. The results are compared with shot gathers from a controlled source experiment (borehole explosions), carried out along the same line. The significant potential of ambient noise analysis, especially with respect to P-wave reflections will be shown and discussed.
    Keywords: 550 - Earth sciences
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    Heterogeneous plate locking in the South-Central Chile subduction zone: Building up the next great earthquake (2011)
    In:  Earth and Planetary Science Letters
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    Publication Date: 2020-02-12
    Description: We use Global Positioning System (GPS) velocities and kinematic Finite Element models (FE-models) to infer the state of locking between the converging Nazca and South America plates in South-Central Chile (36[degree sign]S - 46[degree sign]S) and to evaluate its spatial and temporal variability. GPS velocities provide information on earthquake-cycle deformation over the last decade in areas affected by the megathrust events of 1960 (Mw= 9.5) and 2010 (Mw= 8.8). Our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle: Accordingly, the northern (2010) segment was in a final stage of interseismic loading whereas the southern (1960) segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation. After correcting the signals for mantle relaxation, the residual GPS velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event. Though some similarity exist between locking and 1960 coseismic slip, extrapolating the current, decadal scale slip deficit accumulation towards the ~ 300-yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake. This suggests that either the locking pattern is evolving in time (to reconcile a slip deficit distribution similar to the 1960 earthquake) or that some asperities are not persistent over multiple events. The accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a M ~ 8 event if triggered to fail by stress transfer from the 2010 event.
    Keywords: 550 - Earth sciences
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    The 2010 Granada (Spain) deep earthquake (2011)
    In:  Bulletin of the Seismological Society of America
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Receiver function search for a baby plume in the mantle transition zone beneath the Bohemian Massif (2011)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: The western Bohemian Massif is known for geodynamic phenomena such as earthquake swarms, CO2 dominated free gas emanations of upper-mantle origin, and Tertiary/ Quaternary volcanism. Among other explanations, a small-scale mantle plume has been suggested. We used data from the international passive seismic experiment BOHEMA (2001-2004) and of a previous seismic experiment to investigate the structure of the upper-mantle discontinuities at 410 km and 660 km depth (the ‘410’ and the ‘660’) beneath the Bohemian Massif with the P receiver function method. More than 4500 high-quality receiver function traces could be utilized. Two stacking techniques were used: stacking by station (common station method, CSM) and stacking by piercing points in the mantle transition zone (common conversion point method, CCM). Since the station spacing is very close, rays from different stations have similar piercing points in the mantle transition zone. Therefore CCM is sensitive in the transition zone and CSM is sensitive to the uppermost structure of the mantle. The CSM shows delayed conversion times from the 410 km discontinuity beneath the western Bohemia earthquake region, which indicate a slow uppermost mantle. When stacking our data by CCM, we observe thickening of the transition zone towards the Alpine foreland, which agrees with tomographic results by Piromallo and Morelli. The thickness of the mantle transition zone beneath the western Bohemian Massif is normal, with a faint hint to thinning in the northern part. Our conclusion is that a plume-like structure may exist in the upper mantle below the western Bohemia earthquake region, but with no or only weak imprint on the 410 km discontinuity.
    Keywords: 550 - Earth sciences
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    An improved automatic scheme for empirical baseline correction of digital strong-motion records (2011)
    In:  Bulletin of the Seismological Society of America
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Receiver function study in northern Sumatra and the Malaysian peninsula (2011)
    In:  Journal of Seismology
    Details
    Publication Date: 2020-02-12
    Description: In this receiver function study, we investigate the structure of the crust beneath six seismic broadband stations close to the Sunda Arc formed by subduction of the Indo-Australian under the Sunda plate. We apply three different methods to analyse receiver functions at single stations. A recently developed algorithm determines absolute shear-wave velocities from observed frequency-dependent apparent incidence angles of P waves. Using waveform inversion of receiver functions and a modified Zhu and Kanamori algorithm, properties of discontinuities such as depth, velocity contrast, and sharpness are determined. The combination of the methods leads to robust results. The approach is validated by synthetic tests. Stations located on Malaysia show high-shear-wave velocities (V S) near the surface in the range of 3.4–3.6 km s − 1 attributed to crystalline rocks and 3.6–4.0 km s − 1 in the lower crust. Upper and lower crust are clearly separated, the Moho is found at normal depths of 30–34 km where it forms a sharp discontinuity at station KUM or a gradient at stations IPM and KOM. For stations close to the subduction zone (BSI, GSI and PSI) complexity within the crust is high. Near the surface low V S of 2.6–2.9 km s − 1 indicate sediment layers. High V S of 4.2 km s − 1 are found at depth greater than 6 and 2 km at BSI and PSI, respectively. There, the Moho is located at 37 and 40 km depth. At station GSI, situated closest to the trench, the subducting slab is imaged as a north-east dipping structure separated from the sediment layer by a 10 km wide gradient in V S between 10 and 20 km depth. Within the subducting slab V S ≈ 4.7 km s − 1. At station BSI, the subducting slab is found at depth between 90 and 110 km dipping 20° ± 8° in approximately N 60° E. A velocity increase in similar depth is indicated at station PSI, however no evidence for a dipping layer is found.
    Keywords: 550 - Earth sciences
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    The UNESCO-IOC framework – establishing an international early warning infrastructure in the Indian Ocean region (2010)
    In:  Natural Hazards and Earth System Sciences (NHESS)
    Details
    Publication Date: 2020-02-12
    Description: The Sumatra-Andaman earthquake with a magnitude of 9.3, and the subsequent destructive tsunami which caused more than 225 000 fatalities in the region of the Indian Ocean, happened on 26 December 2004. Less than one month later, the United Nations (UN) World Conference on Disaster Reduction took place in Kobe, Japan to commemorate the 1995 Kobe earthquake. The importance of preparedness and awareness on regional, national and community levels with respect to natural disasters was discussed during this meeting, and resulted in the approval of the Hyogo Declaration on Disaster Reduction. Based on this declaration the UN mandated the Intergovernmental Oceanographic Commission (IOC) of UNESCO (United Nations Education, Science and Cultural Organization), taking note of its over 40 years of successful coordination of the Pacific Tsunami Warning System (PTWC), to take on the international coordination of national early-warning efforts for the Indian Ocean and to guide the process of setting up a Regional Tsunami Early Warning System for the Indian Ocean.
    Keywords: 550 - Earth sciences
    Language: English
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    Wireless technologies for the monitoring of strategic civil infrastructures: an ambient vibration test on the Fatih Sultan Mehmet Suspension Bridge in Istanbul, Turkey (2010)
    In:  Bulletin of Earthquake Engineering
    Details
    Publication Date: 2020-02-12
    Description: Rapid improvements in telemetry technology and the general decrease in communication costs have raised a growing interest in low-cost wireless sensing units. This is especially the case for structural monitoring purposes, where they are becoming a more valuable alternative to conventional wired monitoring system. The main advantages associated with the use of wireless sensing unit include a considerable decrease in installation costs, decentralization of data analysis, and the possibility of broadening the functional capabilities by exploiting the use, at the same time and place, of different sensors. In this work, the design of a low-cost wireless sensing unit able both to collect, analyze, store, and communicate data and estimated parameters is presented. The suitability of a network of these low-cost wireless instruments for monitoring the vibration characteristics and dynamic properties of strategic civil infrastructures is validated during a ambient vibration recording field test on the Fatih Sultan Mehmet Bridge in Istanbul, Turkey.
    Keywords: 550 - Earth sciences
    Language: English
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    Relationship between the InSAR-measured uplift, the structural framework, and the present-day stress field at Lazufre volcanic area, central Andes (2010)
    In:  Tectonophysics
    Details
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Shear wave velocity model of the Santiago de Chile basin derived from ambient noise measurements: A comparison of proxies for seismic site conditions and amplification (2010)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: We determined a high-resolution 3-D S-wave velocity model for a 26 km × 12 km area in the northern part of the basin of Santiago de Chile. To reach this goal, we used microtremor recordings at 125 sites for deriving the horizontal-to-vertical (H/V) spectral ratios that we inverted to retrieve local S-wave velocity profiles. In the inversion procedure, we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements, which were found to vary substantially over short distances in the investigated area. The resulting model was derived by interpolation with a kriging technique between the single S-wave velocity profiles and shows locally good agreement with the few existing velocity profile data, but allows the entire area, as well as deeper parts of the basin, to be represented in greater detail. The wealth of available data allowed us to check if any correlation between the S-wave velocity in the uppermost 30 m (v30S) and the slope of topography, a new technique recently proposed by Wald and Allen, exists on a local scale. We observed that while one lithology might provide a greater scatter in the velocity values for the investigated area, almost no correlation between topographic gradient and calculated v30S exists, whereas a better link is found between v30S and the local geology. Finally, we compared the v30S distribution with the MSK intensities for the 1985 Valparaiso event, pointing out that high intensities are found where the expected v30S values are low and over a thick sedimentary cover. Although this evidence cannot be generalized for all possible earthquakes, it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the Santiago basin.
    Keywords: 550 - Earth sciences
    Language: English
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    Exploring Structural Controls on Sumatran Earthquakes (2010)
    In:  Eos, Transactions American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Description: A series of linked marine and land studies have recently targeted the Sumatra subduction zone, focusing on the 2004 and 2005 plate boundary earthquake ruptures in Indonesia. A collaborative research effort by scientists from the United Kingdom (UK Sumatra Consortium), Indonesia, United States, France, and Germany is focusing on imaging the crustal structure of the margin to examine controls on along-strike and updip earthquake rupture propagation. The fundamental science objective is to examine how margin architecture and properties control earthquake rupture location and propagation.
    Keywords: 550 - Earth sciences
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    The September 2009 Padang earthquake (2010)
    In:  Nature Geoscience
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Rayleigh wave phase velocity maps of Tibet and the surrounding regions from ambient seismic noise tomography (2010)
    In:  Geochemistry Geophysics Geosystems (G3)
    Details
    Publication Date: 2020-02-12
    Description: Ambient noise tomography is applied to the significant data resources now available across Tibet and surrounding regions to produce Rayleigh wave phase speed maps at periods between 6 and 50 s. Data resources include the permanent Federation of Digital Seismographic Networks, five temporary U.S. Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) experiments in and around Tibet, and Chinese provincial networks surrounding Tibet from 2003 to 2009, totaling ∼600 stations and ∼150,000 interstation paths. With such a heterogeneous data set, data quality control is of utmost importance. We apply conservative data quality control criteria to accept between ∼5000 and ∼45,000 measurements as a function of period, which produce a lateral resolution between 100 and 200 km across most of the Tibetan Plateau and adjacent regions to the east. Misfits to the accepted measurements among PASSCAL stations and among Chinese stations are similar, with a standard deviation of ∼1.7 s, which indicates that the final dispersion measurements from Chinese and PASSCAL stations are of similar quality. Phase velocities across the Tibetan Plateau are lower, on average, than those in the surrounding nonbasin regions. Phase velocities in northern Tibet are lower than those in southern Tibet, perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained. At short periods (〈20 s), very low phase velocities are imaged in the major basins, including the Tarim, Qaidam, Junggar, and Sichuan basins, and in the Ordos Block. At intermediate and long periods (〉20 s), very high velocities are imaged in the Tarim Basin, the Ordos Block, and the Sichuan Basin. These phase velocity dispersion maps provide information needed to construct a 3-D shear velocity model of the crust across the Tibetan Plateau and surrounding regions.
    Keywords: 550 - Earth sciences
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    2010 Maule earthquake slip correlates with pre-seismic locking of Andean subduction zone (2010)
    In:  Nature
    Details
    Publication Date: 2020-02-12
    Description: The magnitude-8.8 Maule (Chile) earthquake of 27 February 2010 ruptured a segment of the Andean subduction zone megathrust that has been suspected to be of high seismic potential1,2,3,4,5,6. It is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space-geodetic network before the event. This provides an image of the pre-seismically locked state of the plate interface of unprecedentedly high resolution, allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip. Pre-seismic locking might be used to anticipate future ruptures in many seismic gaps6,7,8,9,10,11,12, given the fundamental assumption that locking and slip are similar. This hypothesis, however, could not be tested without the occurrence of the first gap-filling earthquake. Here we show evidence that the 2010 Maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system (GPS) observations during the previous decade. The earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835. Two regions of high seismic slip (asperities) appeared to be nearly fully locked before the earthquake. Between these asperities, the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip. The rupture stopped in areas that were highly locked before the earthquake but where pre-stress had been significantly reduced by overlapping twentieth-century earthquakes. Our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes, which thus might be anticipated by geodetic observations.
    Keywords: 550 - Earth sciences
    Language: English
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    Lake Toba volcano magma chamber imaged by ambient seismic noise tomography (2010)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Description: For the first time, ambient noise tomography is used to clearly image the magma chamber beneath Lake Toba caldera, one of the largest Quaternary calderas on Earth. Using data from 40 seismic stations deployed between May and October 2008 around Lake Toba, empirical Green's functions are extracted from long term cross-correlations of continuous records. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the period range from 2.5 to 12 seconds. Arrival times of these waves are picked for a given period and inverted using 2-D tomography to calculate lateral variations in velocity for the given period. This was done for six different periods, which all correspond to different sampling depths. Thus the six 2-D models presented together provide information on velocity variations with depth. The results show a low-velocity body coincident with the Lake Toba caldera, representing the magma chamber under the volcano. The chamber is observed to have a complex 3-D geometry, with at least two separate sub-chambers underlying the caldera. Other results include a deep low velocity body, possibly another magma chamber, south west of the lake with an upper limit of ∼7 km depth. The maximum depth to which this body reaches could not be resolved. The Sumatra Fault marks a velocity contrast, but only down to depths not greater than 5 km. The reliability of the results was further confirmed by checkerboard recovery tests.
    Keywords: 550 - Earth sciences
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    Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network (2010)
    In:  Journal of Seismology
    Details
    Publication Date: 2020-02-12
    Description: We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete and surrounding islands. More than 2,500 local and regional events with magnitudes up to M L = 4.5 were recorded during the time period July 2003–June 2004. The magnitude of completeness varies between 1.5 on Crete and adjacent areas and increases to 2.5 in the vicinity of the Strabo trench 100 km south of Crete. Tests with different localization schemes and velocity models showed that the best results were obtained from a probabilistic earthquake localization using a 1-D velocity model and corresponding station corrections obtained by simultaneous inversion. Most of the seismic activity is located offshore of central and eastern Crete and interpreted to be associated with the intracrustal graben system (Ptolemy and Pliny trenches). Furthermore, a significant portion of events represents interplate seismicity along the NNE-ward dipping plate interface. The concentration of seismicity along the Ptolemy and Pliny trenches extends from shallow depths down to the plate interface and indicates active movement. We propose that both trenches form transtensional structures within the Aegean plate. The Aegean continental crust between these two trenches is interpreted as a forearc sliver as it exhibits only low microseismic activity during the observation period and little or no internal deformation. Interplate seismicity between the Aegean and African plates forms a 100-km wide zone along dip from the Strabo trench in the south to the southern shore-line of Crete in the north. The seismicity at the plate contact is randomly distributed and no indications for locked zones were observed. The plate contact below and north of Crete shows no microseismic activity and seems to be decoupled. The crustal seismicity of the Aegean plate in this area is generally confined to the upper 20 km in agreement with the idea of a ductile deformation of the lower crust caused by a rapid return flow of metamorphic rocks that spread out below the forearc. In the region of the Messara half-graben at the south coast of central Crete, a southward dipping seismogenic structure is found that coalesces with the seismicity of the Ptolemy trench at a depth of about 20 km. The accretionary prism south of Crete indicated by the Mediterranean Ridge showed no seismic activity during the observation period and seems to be deforming aseismically.
    Keywords: 550 - Earth sciences
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    Preface 'Outcomes of the RIMAX programme: risk management of extreme flood events' (2010)
    In:  Natural Hazards and Earth System Sciences (NHESS)
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Real-time earthquake monitoring for tsunami warning in the Indian Ocean and beyond (2010)
    In:  Natural Hazards and Earth System Sciences (NHESS)
    Details
    Publication Date: 2020-02-12
    Description: The Mw = 9.3 Sumatra earthquake of 26 December 2004 generated a tsunami that affected the entire Indian Ocean region and caused approximately 230 000 fatalities. In the response to this tragedy the German government funded the German Indonesian Tsunami Early Warning System (GITEWS) Project. The task of the GEOFON group of GFZ Potsdam was to develop and implement the seismological component. In this paper we describe the concept of the GITEWS earthquake monitoring system and report on its present status. The major challenge for earthquake monitoring within a tsunami warning system is to deliver rapid information about location, depth, size and possibly other source parameters. This is particularly true for coast lines adjacent to the potential source areas such as the Sunda trench where these parameters are required within a few minutes after the event in order to be able to warn the population before the potential tsunami hits the neighbouring coastal areas. Therefore, the key for a seismic monitoring system with short warning times adequate for Indonesia is a dense real-time seismic network across Indonesia with densifications close to the Sunda trench. A substantial number of supplementary stations in other Indian Ocean rim countries are added to strengthen the teleseismic monitoring capabilities. The installation of the new GITEWS seismic network – consisting of 31 combined broadband and strong motion stations – out of these 21 stations in Indonesia – is almost completed. The real-time data collection is using a private VSAT communication system with hubs in Jakarta and Vienna. In addition, all available seismic real-time data from the other seismic networks in Indonesia and other Indian Ocean rim countries are acquired also directly by VSAT or by Internet at the Indonesian Tsunami Warning Centre in Jakarta and the resulting "virtual" network of more than 230 stations can jointly be used for seismic data processing. The seismological processing software as part of the GITEWS tsunami control centre is an enhanced version of the widely used SeisComP software and the well established GEOFON earthquake information system operated at GFZ in Potsdam (http://geofon.gfz-potsdam.de/db/eqinfo.php). This recently developed software package (SeisComP3) is reliable, fast and can provide fully automatic earthquake location and magnitude estimates. It uses innovative visualization tools, offers the possibility for manual correction and re-calculation, flexible configuration, support for distributed processing and data and parameter exchange with external monitoring systems. SeisComP3 is not only used for tsunami warning in Indonesia but also in most other Tsunami Warning Centres in the Indian Ocean and Euro-Med regions and in many seismic services worldwide.
    Keywords: 550 - Earth sciences
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    Study of the lithospheric and upper-mantle discontinuities beneath eastern Asia by SS precursors (2010)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: We analyse broad-band SS waveformdata recorded by several networks in Europe with sources mainly in the west Pacific to study the underside reflections of teleseismic SS waves in the lithosphere and the upper mantle beneath eastern Asia and the NW Pacific ocean. SS bounce points sample a corridor from the Aleutian, Kamchatka and Japan subduction zones through the North China Craton and Central Asian Orogenic Belt to the Tibetan plateau. The corridor passes through different tectonic units such as subduction zones, an old continental shield, a fold belt and a high plateau. We investigate the seismic structure of the lithosphere and the mantle transition zone beneath the different geotectonic units along the profile and infer the correlation of geodynamic processes at different depths.We explore the short period frequency content in the SS waveform data and use moveout correction and common midpoint stack to acquire profiles with high lateral and depth resolution from the crust to the mantle transition zone. Clear SS precursors of the 410 and 660 km discontinuities show the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the NW Pacific subduction zones. A low-velocity layer has also been detected beneath the 410 km discontinuity and can be traced along the entire profile. Due to the improved resolution acquired by the method presented here we have been able to study the shallower structures such as the Moho and the lithosphere–asthenosphere boundary by SS precursors. The continental Moho can be clearly seen along this corridor. The depth variation agrees well with earlier receiver function results. We also see negative reflectors along the profile at varying depths, which can be interpreted as the lithosphere–asthenosphere boundary.
    Keywords: 550 - Earth sciences
    Language: English
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    Thickness of the central and eastern European lithosphere as seen by S receiver functions (2010)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: S receiver functions obtained from seismograms of teleseismic events recorded at 78 European permanent broad-band stations are used to estimate the thickness of the European lithosphere. Our results provide new, independent information about the lithospheric thickness beneath the Precambrian platform of Eastern Europe and the Phanerozoic platform of central Europe. Detailed high-resolution images of the lithosphere–asthenosphere boundary (LAB) reveal indications for a typical continental lithosphere of about 100 km thickness beneath a majority of stations within Central Europe, whereas in the vicinity of the Trans-European Suture Zone (TESZ), the lithosphere thickens to about 130 km. A relatively thin lithosphere of 80 km was found beneath the Upper Rhine Graben region suggesting that the Cenozoic extension affects the whole lithosphere. No clear signal from the LAB was detected beneath the Alps and Carpathians. The LAB Sp phase might be disturbed by complicated structure due to ongoing collision/subduction in these regions, or the data are not yet sufficiently dense. A relatively thicker lithosphere of about 120 km was found beneath the SW part of the Bohemian Massif that was formed during the Variscan orogeny.We found an LAB depth of about 190 km near a single station located in the Vrancea area/Eastern Carpathians, which is characterized by the occurrence of intermediate deep earthquakes. Beneath the stations located in the Precambrian platform of Eastern Europe, the LAB deepens to approximately 〉200 km, even though the converted phase from the LAB is not as sharp as found beneath other stations located in Central Europe or even is missing.
    Keywords: 550 - Earth sciences
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    Rapid characterisation of large earthquakes by multiple seismic broadband arrays (2010)
    In:  Natural Hazards and Earth System Sciences (NHESS)
    Details
    Publication Date: 2020-02-12
    Description: An automatic procedure is presented to retrieve rupture parameters for large earthquakes along the Sunda arc subduction zone. The method is based on standard array analysis and broadband seismograms registered within 30°–100° epicentral distance. No assumptions on source mechanism are required. By means of semblance the coherency of P waveforms is analysed at separate large-aperture arrays. Waveforms are migrated to a 10°×10° wide source region to study the spatio-temporal evolution of earthquakes at each array. The multiplication of the semblance source maps resulting at each array increases resolution. Start, duration, extent, direction, and propagation velocity are obtained and published within 25 min after the onset of the event. First preliminary results can be obtained even within 16 min. Their rapid determination may improve the mitigation of the earthquake and tsunami hazard. Real-time application will provide rupture parameters to the GITEWS project (German Indonesian Tsunami Early Warning System). The method is applied to the two M8.0 Sumatra earthquakes on 12 September 2007, to the M7.4 Java earthquake on 2 September 2009, and to major subduction earthquakes that have occurred along Sumatra and Java since 2000. Obtained rupture parameters are most robust for the largest earthquakes with magnitudes M≥8. The results indicate that almost the entire seismogenic part of the subduction zone off the coast of Sumatra has been ruptured. Only the great Sumatra event in 2004 and the M7.7 Java event on 17 July 2006 could reach to or close to the surface at the trench. Otherwise, the rupturing was apparently confined to depths below 25 km. Major seismic gaps seem to remain off the coast of Padang and the southern tip of Sumatra.
    Keywords: 550 - Earth sciences
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    Stable isotopes in understanding origin and degradation processes of petroleum (2010)
    In:  Handbook of Hydrocarbon and Lipid Microbiology
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    Publication Date: 2020-02-12
    Description: In this essay we provide a short introduction to and overview of the basics of stable isotope geochemistry and its common application in petroleum geochemistry. We identify the processes that are responsible for the carbon and hydrogen isotopic compositions of biological and geological organic matter and indicate the utility of stable isotopes in oil-source rock correlations. Stable isotope analyses are also exploited in the investigation of different alteration processes within oils and petroleum reservoirs. State of the art work is presented, and future research needs are identified.
    Keywords: 550 - Earth sciences
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    Suitability of rapid energy magnitude determinations for emergency response purposes (2010)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: It is common practice in the seismological community to use, especially for large earthquakes, the moment magnitude Mw as a unique magnitude parameter to evaluate the earthquake’s damage potential. However, as a static measure of earthquake size, Mwdoes not provide direct information about the released seismicwave energy and its high frequency content,which is the more interesting information both for engineering purposes and for a rapid assessment of the earthquake’s shaking potential. Therefore, we recommend to provide to disaster management organizations besides Mw also sufficiently accurate energy magnitude determinations as soon as possible after large earthquakes. We developed and extensively tested a rapid method for calculating the energy magnitude Me within about 10–15 min after an earthquake’s occurrence. The method is based on pre-calculated spectral amplitude decay functions obtained from numerical simulations of Green’s functions. After empirical validation, the procedure has been applied offline to a large data set of 767 shallow earthquakes that have been grouped according to their type of mechanism (strike-slip, normal faulting, thrust faulting, etc.). The suitability of the proposed approach is discussed by comparing our rapid Me estimates with Mw published by GCMT as well as with Mw and Me reported by the USGS. Mw is on average slightly larger than our Me for all types of mechanisms. No clear dependence on source mechanism is observed for our Me estimates. In contrast, Me from the USGS is generally larger than Mw for strike-slip earthquakes and generally smaller for the other source types. For ∼67 per cent of the event data set our Me differs ≤ ±0.3 magnitude units (m.u.) from the respective Me values published by the USGS. However, larger discrepancies (up to 0.8 m.u.) may occur for strike-slip events. A reason of that may be the overcorrection of the energy flux applied by the USGS for this type of earthquakes. We follow the original definition of magnitude scales, which does not apply a priori mechanism corrections to measured amplitudes, also since reliable fault-plane solutions are hardly available within 10–15 min after the earthquake origin time. Notable is that our uncorrected Me data show a better linear correlation and less scatter with respect to Mw than Me of the USGS. Finally, by analysing the recordings of representative recent pairs of strong and great earthquakes, we emphasize the importance of combining Mw and Me in the rapid characterization of the seismic source. They are related to different aspects of the source and may differ occasionally even more than 1 m.u. This highlights the usefulness and importance of providing these two magnitude estimates together for a better assessment of an earthquake’s shaking potential and/or tsunamigenic potential.
    Keywords: 550 - Earth sciences
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    Deblurring of frequency-wavenumber images from small-scale seismic arrays (2010)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: Temporary arrays installed in urban areas for investigating the upper-most geological structure typically comprised of a limited number of stations and are arranged in geometries constrained by environmental boundaries. Therefore, it is expected that the frequency–wavenumber images are significantly blurred by the array transfer function and are corrupted by noise. In this paper, the effect of the Richardson–Lucy regularization method applied to the problem of deblurring frequency–wavenumber images is investigated. The images are computed by analysing data from two small-aperture 2-D arrays, installed with different configurations in a test-site within the town of Potenza (Southern Italy) for near-surface investigations. We show that removing the effects of the array response from the frequency–wavenumber images improve the phase-velocity estimation, reducing the relevant level of uncertainty. Furthermore, the Richardson–Lucy regularization method is effective in reducing the level of noise related to spatial aliasing by eliminating spurious peaks, allowing the maxima related to different seismic sources to be better discriminated.
    Keywords: 550 - Earth sciences
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    Risk management of extreme flood events (2010)
    In:  Natural Hazards and Earth System Sciences (NHESS)
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Subduction earthquake deformation associated with 14 November 2007, Mw 7.8 Tocopilla earthquake in Chile: Results from InSAR and aftershocks (2010)
    In:  Tectonophysics
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Locating non-volcanic tremor along the San Andreas Fault using a multiple array source imaging technique (2010)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: Non-volcanic tremor (NVT) has been observed at several subduction zones and at the San Andreas Fault (SAF). Tremor locations are commonly derived by cross-correlating envelope-transformed seismic traces in combination with source-scanning techniques. Recently, they have also been located by using relative relocations with master events, that is low-frequency earthquakes that are part of the tremor; locations are derived by conventional traveltime-based methods. Here we present a method to locate the sources of NVT using an imaging approach for multiple array data. The performance of the method is checked with synthetic tests and the relocation of earthquakes. We also applied the method to tremor occurring near Cholame, California. A set of small-aperture arrays (i.e. an array consisting of arrays) installed around Cholame provided the data set for this study. We observed several tremor episodes and located tremor sources in the vicinity of SAF. During individual tremor episodes, we observed a systematic change of source location, indicating rapid migration of the tremor source along SAF.
    Keywords: 550 - Earth sciences
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    Volcano deformation analysis at the Lazufre volcanic area (central Andes) using geodetic and geological observations (2010)
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    Publication Date: 2020-02-12
    Description: Large-scale volcanic deformation recently detected by radar interferometry (InSAR) provides new information and thus new scientific challenges for understanding volcano-tectonic activity and magmatic systems. The destabilization of such a system at depth noticeably affects the surrounding environment through magma injection, ground displacement and volcanic eruptions. To determine the spatiotemporal evolution of the Lazufre volcanic area located in the central Andes, we combined short-term ground displacement acquired by InSAR with long-term geological observations. Ground displacement was first detected using InSAR in 1997. By 2008, this displacement affected 1800 km2 of the surface, an area comparable in size to the deformation observed at caldera systems. The original displacement was followed in 2000 by a second, small-scale, neighbouring deformation located on the Lastarria volcano. We performed a detailed analysis of the volcanic structures at Lazufre and found relationships with the volcano deformations observed with InSAR. We…zeige mehr
    Description: Vulkanische Deformationen in großem Maßstab, die mittels InSAR gemessen wurden, liefern neue Informationen und dadurch einen neuen Blickwinkel auf vulkan-tektonische Aktivitäten und das Verständnis von langlebigen, magmatischen Systemen. Die Destabilisierung eines solchen Systems in der Tiefe beeinflusst dauerhaft die Oberfläche durch Versatz des Bodens, magmatische Einflüsse und vulkanische Unruhen. Mit der Kombination aus kleinräumigem Bodenversatz gemessen mittels InSAR, numerischer Modellierung und langfristigen geologischen Beobachtungen, analysieren wir die Gegend um den Vulkan Lazufre in den Zentralanden, um die raumzeitliche Entwicklung der Region zu bestimmen. Bodenversatz wurde hierbei im Jahr 1997 mittels Radar-Interferrometrie (InSAR) gemessen, was eine Fläche von 1800 km² ausmacht, vergleichbar mit der Größe der Deformation des Kraters. Im Jahr 2000 wurde zusätzlich eine kleinräumige Deformation am Nachbarvulkan Lastarria entdeckt. Wir sehen räumliche als auch zeitliche Verbindungen zwischen der Deformation…zeige mehr
    Keywords: 550 - Earth sciences
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    The Fine Structure of the Subducted Investigator Fracture Zone in Western Sumatra as Seen by Local Seismicity (2010)
    In:  Earth and Planetary Science Letters
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    Publication Date: 2020-02-12
    Description: The Sumatran margin suffered three great earthquakes in recent years (Aceh-Andaman 26 December 2004 Mw = 9.1, Nias 28 March 2005 Mw = 8.7, Bengkulu 12 September 2007 Mw = 8.5). Here we present local earthquake data from a dense, amphibious local seismic network covering a segment of the Sumatran margin that last ruptured in 1797. The occurrence of forearc islands along this part of the Sumatran margin allows the deployment of seismic land-stations above the shallow part of the thrust fault. In combination with ocean bottom seismometers this station geometry provides high quality hypocentre location for the updip end of the seismogenic zone in an area where geodetic data are also available. In this region, the Investigator Fracture Zone (IFZ), which consists of 4 sub-ridges, is subducted below the Sunda plate. This topography appears to influence seismicity at all depth intervals. A well-defined linear streak of seismicity extending from 80 to 200 km depth lies along the prolongation of closely spaced IFZ sub-ridges. More intermediate depth seismicity is located to the southeast of this string of seismicity and is related to subducted rough oceanic seafloor. The plate interface beneath Siberut Island which ruptured last in 1797 is characterised by almost complete absence of seismicity.
    Keywords: 550 - Earth sciences
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    Kinematic rupture process of the 2007 Tocopilla earthquake and its main aftershocks from teleseismic and strong-motion data (2010)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: We study a large Mw= 7.6 earthquake that occurred on 2007 November 14 in the Northern Chile seismic gap near the city of Tocopilla. Using a variety of seismic data we show that this earthquake ruptured only the lower part of the interplate seismic zone and generated a series of plate interface aftershocks. Two large aftershocks on 2007 November 15 ruptured the interplate zone oceanwards of the Mejillones Peninsula, a major geographical feature in the Antofagasta region. On 2007 December 16, a large Mw= 6.8 aftershock, that occurred near the southern bottom of the fault plane of the main event, is shown to be a slab-push earthquake located inside the subducted Nazca Plate and triggered by along slab compression. Aftershocks of this event demonstrate that it occurred on an almost vertical fault. The Tocopilla earthquake took place just after the installation of a new seismological network by Chilean, German and French researchers. The accelerometric data combined with far field seismic data provide a quite complete and consistent view of the rupture process. The earthquake broke a long (130 km) and narrow (about 30–50 km) zone of the plate interface just above the transition zone. Using a non-linear kinematic inversion method, we determined that rupture occurred on two well-defined patches of roughly elliptical shape. We discuss the consequences of this event for models of gap filling earthquakes in Chile proposed in the 1970s.
    Keywords: 550 - Earth sciences
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    Structure of the seismogenic zone of the southcentral Chilean margin revealed by local earthquake traveltime tomography (2009)
    In:  Journal of Geophysical Research
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    Publication Date: 2020-02-12
    Description: We use traveltime data of local earthquakes and controlled sources observed by a large, temporary, amphibious seismic network to reveal the anatomy of the southcentral Chilean subduction zone (37–39°S) between the trench and the magmatic arc. At this location the giant 1960 earthquake (M = 9.5) nucleated and ruptured almost 1000 km of the subduction megathrust. For the three-dimensional tomographic inversion we used 17,148 P wave and 10,049 S wave arrival time readings from 439 local earthquakes and 94 shots. The resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests. The downgoing lithosphere is delineated by high seismic P wave velocities. High v p/v s ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle. The subducting oceanic crust can be traced down to a depth of 80 km, as indicated by a low velocity channel. The continental crust extends to approximately a 50-km depth near the intersection with the subducting plate. This suggests a wide contact zone between continental and oceanic crust of about 150 km, potentially supporting the development of large asperities. Eastward the crustal thickness decreases again to a minimum of about a 30-km depth. Relatively low v p/v s at the base of the forearc does not support a large-scale serpentinization of the mantle wedge. Offshore, low v p and high v p/v s reflect young, fluid-saturated sediments of forearc basins and the accretionary prism.
    Keywords: 550 - Earth sciences
    Language: English
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    Empirical site-specific response-spectra correction factors for the Gubbio basin (Central Italy) (2009)
    In:  Soil Dynamics and Earthquake Engineering
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    Publication Date: 2020-02-12
    Description: Providing quantitative microzonation results that can be taken into account in urban land-use plans is a challenging task that requires collaborative efforts between the seismological and engineering communities. In this study, starting from the results obtained by extensive geophysical and seismological investigations, we propose and apply an approach to the Gubbio basin (Italy) that can be easily implemented for cases of moderate-to-low ground motion and that takes into account not only simple 1D, but also more complicated 3D effects. With this method, the sites inside the basin are classified by their fundamental resonance frequencies, estimated from the horizontal-to-vertical spectral ratio applied to noise recordings (HVNSR). The correspondence between estimates of the fundamental frequency from this method and those derived from earthquake recordings was verified at several calibration sites. The amplification factors used to correct the response spectra are computed by the ratio between the response spectra at sites within the basin and the response spectra at a hard-rock site using data from two seismic transects. Empirical amplification functions are then assigned to the fundamental frequencies after applying an interpolation technique. The suitability of the estimated site-specific correction factors for response spectra was verified by computing synthetic response spectra for stations within the basin, starting from the synthetic recording at a nearby rock station, and comparing them with observed ones.
    Keywords: 550 - Earth sciences
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    I-GET Integrated Geophyiscal Exploration Technologies : Final Conference ; Geophysics and Geology in Geothermal Exploration ; Conference Contributions (2009)
    GFZ German Research Centre for Geosciences
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Language: English
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    Deep structure of the western South African passive margin - Results of a combined approach of seismic, gravity and isostatic investigations. (2009)
    In:  Tectonophysics
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    Publication Date: 2020-02-12
    Description: The passive margin of the South Atlantic shows typical features of a rifted volcanic continental margin, encompassing seaward dipping reflectors, continental flood basalts and high-velocity/density lower crust at the continent–ocean transition, probably emplaced during initial seafloor spreading in the Early Cretaceous. The Springbok profile offshore western South Africa is a combined transect of reflection and refraction seismic data. This paper addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives. The velocity modelling revealed a segmentation of the margin into three distinct parts of continental, transitional and oceanic crust. As observed at many volcanic margins, the lower crust is characterised by a zone of high velocities with up to 7.4 km/s. The conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities, found to be 3100 kg/m3. Both approaches identified the body to have a thickness of about 10 km. Yet, the gravity modelling predicted the transition between the high-density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal. Finally, isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced. The results imply isostatic equilibrium over large parts of the profile, smaller deviations are supposed to be compensated regionally. The calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km.
    Keywords: 550 - Earth sciences
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    Anisotropic structure beneath central Java from local earthquake tomography (2009)
    In:  Geochemistry Geophysics Geosystems (G3)
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    Publication Date: 2020-02-12
    Description: In this study we present the new tomographic code ANITA which provides 3-D anisotropic P and isotropic S velocity distribution based on P and S traveltimes from local seismicity. For the P anisotropic model, we determine four parameters for each parameterization cell. This represents an orthorhombic anisotropy with one predefined direction oriented vertically. Three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0°, 60°, and 120°, and one is a perturbation along the vertical axis. The nonlinear iterative inversion procedure is similar to that used in the LOTOS code. We have implemented this algorithm for the updated data set of central Java, part of which was previously used for the isotropic inversion. It was obtained that the crustal and uppermost mantle velocity structure beneath central Java is strongly anisotropic with 7–10% of maximal difference between slow and fast velocity in different directions. In the forearc (area between southern coast and volcanoes), the structure of both isotropic and anisotropic structure is strongly heterogeneous. Variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust. Beneath volcanoes we observe faster velocities in vertical direction, which is probably an indicator for vertically oriented structures (channels, dykes). In the crust beneath the middle part of central Java, north to Merapi and Lawu volcanoes, we observe a large and very intense anomaly with a velocity decrease of up to 30% and 35% for P and S models, respectively. Inside this anomaly E-W orientation of fast velocity takes place, probably caused by regional extension stress regime. In a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and/or penetration of quasi-horizontal lenses with molten magma. In the mantle, trench parallel anisotropy is observed throughout the study area. Such anisotropy in the slab entrained corner flow may be due to presence of B-type olivine having predominant axis parallel to the shear direction, which appears in conditions of high water or/and melting content.
    Keywords: 550 - Earth sciences
    Language: English
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    Microseismicity at the North Anatolian Fault in the Sea of Marmara offshore Istanbul, NW Turkey (2009)
    In:  Journal of Geophysical Research
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    Publication Date: 2020-02-12
    Description: The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara forms a “seismic gap” where a major earthquake is expected to occur in the near future. This segment of the fault lies between the 1912 Ganos and 1999 İzmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismic activity at the main fault branch offshore of Istanbul below the Çınarcık Basin, a permanent seismic array (PIRES) was installed on the two outermost Prince Islands, Yassiada and Sivriada, at a few kilometers distance to the fault. In addition, a temporary network of ocean bottom seismometers was deployed throughout the Çınarcık Basin. Slowness vectors are determined combining waveform cross correlation and P wave polarization. We jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision. We observe seismicity rates of 20 events per month for M 〈 2.5 along the basin. The spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the Çınarcık Basin merge to one single master fault below ∼17 km depth. On the basis of a cross-correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations. Fault plane solutions have a predominant right-lateral strike-slip mechanism, indicating that normal faulting along this part of the NAFZ plays a minor role. Toward the west we observe increasing components of thrust faulting. This supports the model of NW trending, dextral strike-slip motion along the northern and main branch of the NAFZ below the eastern Sea of Marmara.
    Keywords: 550 - Earth sciences
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    Stress transfer in the Lazufre volcanic area, Central Andes (2009)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Escala Macrosísmica Europea 1998 = European Macroseismic Scale 1998 : EMS-98 (2009)
    Centre Européen de Géodynamique et de Séismologie
    In:  Cahiers du Centre Européen de Géodynamique et de Séismologie
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Language: Spanish
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    Precise location of San Andreas Fault tremors near Cholame, California using seismometer clusters: Slip on the deep extension of the fault? (2009)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Description: We examine a 24-hour period of active San Andreas Fault (SAF) tremor and show that this tremor is largely composed of repeated similar events. Utilizing this similarity, we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake (LFE) “master template,” located using P and S wave arrivals to be ∼26 km deep. To compensate for low signal-to-noise, we estimate event-pair differential times at “clusters” of nearby stations rather than at single stations. We find that the locations form a near-linear structure in map view, striking parallel to the SAF and near the surface trace. Therefore, we suggest that at least a portion of the tremor occurs on the deep extension of the fault, likely reflecting shear slip, similar to subduction zone tremor. If so, the SAF may extend to the base of the crust, ∼10 km below the deepest regular earthquakes on the fault.
    Keywords: 550 - Earth sciences
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    Impact of megathrust geometry on inversion of coseismic slip from geodetic data : Application to the 1960 Chile earthquake (2009)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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    Combination of Acceleration-Sensor and Broadband Velocity-Sensor Recordings for Attenuation Studies: The Case of the 8 January 2006 Kythera Intermediate-Depth Earthquake (2009)
    In:  Bulletin of the Seismological Society of America
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    Publication Date: 2020-02-12
    Description: On 8 January 2006, an intermediate-depth earthquake occurred at the western part of the Hellenic trench close to the island of Kythera (southern Greece). This is the first intermediate-depth earthquake in the broader Aegean area that has produced such an extensive set of useful recordings, as it was recorded by the main permanent seismological networks and numerous acceleration sensors operating in Greece, as well as by EGELADOS, a large-scale temporary amphibian broadband seismological network deployed in the southern Aegean area. An effort to combine all the available data (broadband velocity and acceleration sensor) was made to study the properties of ground-motion attenuation of this earthquake. The combination of both types of data revealed interesting properties of the earthquake wave field, which would remain hidden if only one type of data was used. Moreover, the data have been used for a validation of existing peak ground-motion empirical prediction relations and the preliminary study of the very inhomogeneous attenuation pattern of the southern Aegean intermediate-depth events at both near- and far-source distances
    Keywords: 550 - Earth sciences
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    Receiver function images from the Moho and the slab beneath the Altiplano and Puna plateaus in the Central Andes (2009)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: Teleseismic data recorded during one and a half years are investigated with the receiver function technique to determine the crustal and upper-mantle structures underneath the highly elevated Altiplano and Puna plateaus in the central Andes. A series of converting interfaces are determined along two profiles at 21°S and 25.5°S, respectively, with a station spacing of approximately 10 km. The data provide the highest resolution gained from a passive project in this area, so far. The oceanic Nazca plate is detected down to 120 km beneath the Altiplano whereas beneath the Puna, the slab can unexpectedly be traced down to 200 km depth at longer periods. A shallow crustal low-velocity zone is determined beneath both plateaus exhibiting segmentation. In the case of the Altiplano, the segments present vertical offsets and are separated by inclined interfaces, which coincide with major fault systems at the surface. An average depth to Moho of about 70 km is determined for the Altiplano plateau. A strong negative velocity anomaly located directly below the Moho along with local crustal thinning is interpreted beneath the volcanic arc of the Altiplano plateau between 67°W and 68.5°W. A deep section of the Puna profile reveals thinning of the mantle transition zone. Although poorly resolved, the detected anomaly may suggest the presence of a mantle plume, which may constitute the origin of the anomalous temperatures at the depth of the upper-mantle discontinuities.
    Keywords: 550 - Earth sciences
    Language: English
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    Characterization of shallow geology by high-frequency seismic noise tomography (2009)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: To study the applicability of the passive seismic interferometry technique to near-surface geological studies, seismic noise recordings from a small scale 2-D array of seismic stations were performed in the test site of Nauen (Germany). Rayleigh wave Green's functions were estimated for different frequencies. A tomographic inversion of the traveltimes estimated for each frequency from the Green's functions is then performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved at engineering–geotechnical scales. Furthermore, a 2-D S-wave velocity cross-section is obtained by combining 1-D velocity structures derived from the inversion of the dispersion curves extracted at several points along a profile where other geophysical analyses were performed. It is shown that the cross-section from passive seismic interferometry provides a clear image of the local structural heterogeneities that are in excellent agreement with georadar and geoelectrical results. Such findings indicate that the interferometry analysis of seismic noise is potentially of great interest for deriving the shallow 3-D velocity structure in urban areas.
    Keywords: 550 - Earth sciences
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    Crustal structure of the southern Dead Sea basin derived from project DESIRE wide-angle seismic data (2009)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: As part of the DEad Sea Integrated REsearch project (DESIRE) a 235 km long seismic wide-angle reflection/refraction (WRR) profile was completed in spring 2006 across the Dead Sea Transform (DST) in the region of the southern Dead Sea basin (DSB). The DST with a total of about 107 km multi-stage left-lateral shear since about 18 Ma ago, accommodates the movement between the Arabian and African plates. It connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a length of about 1 100 km. With a sedimentary infill of about 10 km in places, the southern DSB is the largest pull-apart basin along the DST and one of the largest pull-apart basins on Earth. The WRR measurements comprised 11 shots recorded by 200 three-component and 400 one-component instruments spaced 300 m to 1.2 km apart along the whole length of the E–W trending profile. Models of the P-wave velocity structure derived from the WRR data show that the sedimentary infill associated with the formation of the southern DSB is about 8.5 km thick beneath the profile. With around an additional 2 km of older sediments, the depth to the seismic basement beneath the southern DSB is about 11 km below sea level beneath the profile. Seismic refraction data from an earlier experiment suggest that the seismic basement continues to deepen to a maximum depth of about 14 km, about 10 km south of the DESIRE profile. In contrast, the interfaces below about 20 km depth, including the top of the lower crust and the Moho, probably show less than 3 km variation in depth beneath the profile as it crosses the southern DSB. Thus the Dead Sea pull-apart basin may be essentially an upper crustal feature with upper crustal extension associated with the left-lateral motion along the DST. The boundary between the upper and lower crust at about 20 km depth might act as a decoupling zone. Below this boundary the two plates move past each other in what is essentially a shearing motion. Thermo-mechanical modelling of the DSB supports such a scenario. As the DESIRE seismic profile crosses the DST about 100 km north of where the DESERT seismic profile crosses the DST, it has been possible to construct a crustal cross-section of the region before the 107 km left-lateral shear on the DST occurred.
    Keywords: 550 - Earth sciences
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    Relationship between the upper mantle high velocity seismic lid and the continental lithosphere (2009)
    In:  Lithos
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    Publication Date: 2020-02-12
    Description: The lithosphere-asthenosphere boundary corresponds to the base of the “rigid” plates – the depth at which heat transport changes from advection in the convecting deeper upper mantle to conduction in the shallow upper mantle. Although this boundary is a fundamental feature of the Earth, mapping it has been difficult because it does not correspond to a sharp change in temperature or composition. Various definitions of the lithosphere and asthenosphere are based on the analysis of different types of geophysical and geological observations. The depth to the lithosphere-asthenosphere boundary determined from these different observations often shows little agreement when they are applied to the same region because the geophysical and geological observations (i.e., seismic velocity, strain rate, electrical resistivity, chemical depletion, etc.) are proxies for the change in rheological properties rather than a direct measure of the rheological properties. In this paper, we focus on the seismic mapping of the upper mantle high velocity lid and low velocity zone and its relationship to the lithosphere and asthenosphere. We have two goals: (a) to examine the differences in how teleseismic body-wave travel-time tomography and surface-wave tomography image upper mantle seismic structure; and (b) to summarise how upper mantle seismic velocity structure can be related to the structure of the lithosphere and asthenosphere. Surface-wave tomography provides reasonably good depth resolution, especially when higher modes are included in the analysis, but lateral resolution is limited by the horizontal wavelength of the long-period surface waves used to constrain upper mantle velocity structure. Teleseismic body-wave tomography has poor depth resolution in the upper mantle, particularly when no strong lateral contrasts are present. If station terms are used, features with large lateral extent and gradual boundaries are attenuated in the tomographic image. Body-wave models are not useful in mapping the thickness of the high velocity upper mantle lid because this type of analysis often determines wave speed perturbations from an unknown horizontal average and not absolute velocities. Thus, any feature which extends laterally across the whole region beneath a seismic network becomes invisible in the Teleseismic body-wave tomographic image. We compare surface-wave and body-wave tomographic results using southern Africa as an example. Surface-wave tomographic images for southern Africa show a strong, high velocity upper mantle lid confined to depths shallower than ~200 km, whereas body-wave tomographic images show weak high velocity in the upper mantle extending to depths of ~300 km or more. However, synthetic tests show that these results are not contradictory. The absolute seismic velocity structure of the upper mantle provided by surface wave analysis can be used to map the thermal lithosphere. Priestley and McKenzie (Priestley, K., McKenzie, D., 2006. The thermal structure of the lithosphere from shear wave velocities. Earth and Planetary Science Letters 244, 285–301.) derive an empirical relationship between shear wave velocity and temperature. This relationship is used to obtain temperature profiles from the surfacewave tomographic models of the continental mantle. The base of the lithosphere is shown by a change in the gradient of the temperature profiles indicative of the depth where the mode of heat transport changes from conduction to advection. Comparisons of the geotherms determined from the conversion of surface-wave wave speeds to temperatures with upper mantle nodule-derived geotherms demonstrate that estimates of lithospheric thickness from Vs and from the nodule mineralogy agree to within about 25 km. The Lithospheric thickness map for Africa derived from the surface-wave tomographic results shows that thick lithosphere underlies most of the Archean crust in Africa. The distribution of diamondiferous kimberlites provides an independent estimate of where thick lithosphere exists. Diamondiferous kimberlites generally occur where the lower part of the thermal lithosphere as indicated by seismology is in the diamond stability field.
    Keywords: 550 - Earth sciences
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    PASSEQ 2006-2008: Passive seismic experiment in Trans-European Suture Zone (2008)
    In:  Studia Geophysica et Geodaetica
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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  • 97
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    First seismic record for intra-arc strike-slip tectonics along the Liquiñe-Ofqui fault zone at the obliquely convergent plate margin of the southern Andes (2008)
    In:  Tectonophysics
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    Publication Date: 2020-02-12
    Description: A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to M(tief)w 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent M(tief)w 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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  • 98
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    A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California (2008)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Description: Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected.We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is locatedNEof the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal highconductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF.We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being 5–8 km wide and reaching to depths 〉7 km, in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity ∼15 km SW of the SAF and likely represents a deep-reaching fault zone.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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  • 99
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    Rapid determination of ME for strong to great shallow earthquakes (2008)
    In:  Geophysical Research Letters
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    Publication Date: 2020-02-12
    Description: We propose a new rapid procedure for determining the energy magnitude Me for shallow events from broadband teleseismic P-wave signals within the distance range 20°–98°. To accomplish this task, we compute spectral amplitude decay functions for different periods using numerical simulations based on the reference Earth model AK135Q. By means of these functions, we correct the spectra of the teleseismic recordings for the propagation path effects, and calculate the radiated seismic energy ES, and hence Me. We use cumulative P-wave windows for simulating a real- or near real-time procedure and test it for 61 shallow earthquakes. The results show that our approach is able to provide a rapid and reliable Me determination within 7–15 minutes after the earthquake origin time, and is therefore suitable for implementation in rapid response systems.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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  • 100
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    S velocity structure and radial anisotropy in the Aegean region from surface wave dispersion (2008)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: The lithospheric structure of the Aegean region is investigated by analysis of Rayleigh-wave fundamental mode dispersion measurements. Isotropic 1-D models for almost 100 two-station ray paths across the region display distinct variations in the Moho depth and crustal S-wave velocities. The descending slab of the subducting African plate can be resolved down to 120 km depth beneath the volcanic arc. Three different regions are distinguished in terms of Moho depth: (1) The forearc, with large crustal thicknesses between 38 and 48 km and an average of 43 km, (2) the northern Aegean, with an average Moho depth of 28 km and (3) the southern Aegean (central volcanic arc, i.e. Cyclades, and Sea of Crete) with an even thinner crust of around 25 km. Lateral variations in structure between 25 and 55 km depth indicate a marked difference between the western and eastern forearc, collocated with pronounced changes in trench and slab geometry as well as published deformation rates. S velocities between 25 and 55 km depth are low everywhere beneath the forearc but increase from the Peleponnesus to Crete. An abrupt change occurs between western and central Crete in terms of the visibility of the Aegean Moho and the seismic structure of the lithospheric mantle wedge: An Aegean mantle wedge with S velocities above 4.4 km s−1 is only observed to the east of central Crete, whereas to the west velocities of less than 4.0 km s−1 occur down to the plate contact. These low velocities above the slab may indicate the presence of a melange of metamorphic rocks at the depths. A low-velocity asthenospheric layer is observed beneath the Sea of Crete and the Cyclades below 40 km depth, between the thinned lithosphere above and the slab below. The observed radial anisotropy in the northern part of the Aegean is likely to be due to preferred orientation of anisotropic minerals within the lower crust, possibly caused by lateral ductile flow associated with recent lithospheric extension.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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