ALBERT

Description: 〈h3〉Abstract〈/h3〉 〈p〉The present-day stress field in Egypt has been investigated on the basis of updated earthquake focal mechanism catalog covering the period from 1951 to 2017. Our catalog contains 234 focal mechanisms compiled from previous studies in addition to 22 new source mechanism solutions achieved in this study. According to the distribution of the recent earthquake epicentres, Egypt is divided into nine seismotectonic regions. The available fault plane solutions in Egypt demonstrate a spatial variability of source mechanisms, which categorize the study area into three groups. The first group includes Dahshour, Beni Suef, Cairo-Suez district, Northern-Central Gulf of Suez and Southern Gulf of Suez, which characterized by pure normal faulting mechanism to normal faulting with strike-slip component. Pure strike-slip faulting has clearly characterised Aswan and Gulf of Aqaba regions in the second group. However, the third group, which contains Abu Dabbab and the northern Egyptian continental margin, is characterized by thrust and strike-slip faulting. To calculate the orientation of the principle stress axes and the shape ratio we have applied the stress inversion technique. The present-day stress regime shows a variability of the tectonic stresses including extensional tectonic, transtensional and strike-slip. The transtensional stress regime with a maximum horizontal extensional NNE stress axis represents the dominant stress field pattern in Egypt. The results exhibit a good agreement with the tectonic settings and recent deformations in Egypt.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Seismic hazard assessment is one of the main targets of seismological research, aiming to contribute to reducing the catastrophic consequences of strong earthquakes (e.g., 〈span〉 〈span〉\( M \ge 6.0 \)〈/span〉 〈/span〉). From the early stage of seismological research, both purely seismological and statistical methods were adopted for seismic hazard assessment. An approach towards this target was attempted by means of network theory, aiming to provide insight into the complex physical mechanisms that cause earthquakes and whether the occurrence of strong earthquakes can be predicted to some extent. Application of network theory in different areas of the world with intense seismic activity, such as Japan, California, Italy, Greece, Iran, and Chile, has yielded promising results that have negligible probability of being obtained by purely random guessing.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Asperity models for ground motion prediction is widely used in Japan. Here we expand the application of these asperity models to predict fault displacement caused by surface rupture. The proposed approach is rather simple and practical for the use in fault displacement hazard analysis in nuclear installations and other critical infrastructures, as it is the emphasis of the current topical issue. The proposed method mainly consists of two steps. The first step consists in the characterization of asperities at the seismogenic zone based on the kinematic asperity source model following Irikura’s recipe (Irikura and Miyake in Pure Applied Geophysics, 168:85–104, 2011) for strong ground motion prediction. Since the kinematic model does not take into account surface rupture mechanism, this first step assumes that the fault is buried, and then by trial and error procedure the stress drop on the asperities are estimated, so that the average slip at each asperity be consistent with the ones from the kinematic model. At this stage, the dynamic model predicts strong ground motion consistent with those from the kinematic model. In the second step, the surface rupture is included by calibrating the shallow layer (SL) with stress drop, strength excess and critical slip distance, so that the final fault displacement along the fault be consistent with observations. The 2010 Mw 7.0 Darfield (New Zealand) earthquake is used to test the proposed method. Surface-rupturing was observed in several sites along the main fault reaching values of fault displacement larger than 5 m. The main fault of this earthquake is strike-slip, almost vertical. Therefore, a simplified planar fault asperity model to capture the main features of the fault displacement is assumed. The fault dimensions are assumed to have a length of 60 km and a width of 24 km with three asperities. The preferred model of the first step predicts average slip for each asperity of 2.7, 2.7, and 2 m corresponding, respectively, to stress drops of 6.0 MPa, 8.5 MPa, and 7.0 MPa. In the second step, the surface rupture is calibrated assuming a SL zone of 3 km depth. We found that negative stress drop is not necessary in the SL, because this strongly inhibits surface rupturing. Our preferred model produces fault displacement distribution closer to the observed ones, but average slip at each asperity increases to 3.4 m, 3.2 and 2.8 m. This increase in average slip is due to the contribution of surface rupturing. Ground motion differences between fault-surface rupturing and buried models are negligible, except at the very near-source. These differences are attributed to the SL rupture that mainly affect the ground motion at the very near-source. Overall, our simple asperity model captures the main features of the observed fault displacement and near-source ground motion, proving that the proposed simple and practical two step-procedure provides meaningful estimate of fault displacement and near-source ground motion consistent with observations, as such, this method has the potential to be used in practical fault displacement hazard analysis.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉It is commonly accepted that the horizontal-to-vertical spectral ratio (HVSR) technique enables the detection of the fundamental resonance frequency (〈span〉 〈span〉\(f_{\text{HVSR}}\)〈/span〉 〈/span〉) of a given site. The utility of this 〈span〉 〈span〉\(f_{\text{HVSR}}\)〈/span〉 〈/span〉 is analyzed using the nonlinear regression relationships between 〈span〉 〈span〉\(f_{\text{HVSR}}\)〈/span〉 〈/span〉 and bedrock depth (〈span〉 〈span〉\(h\)〈/span〉 〈/span〉). The derived relationships are mostly site-specific, so that the present paper consists of two main parts. The first is a literature review for the available empirical relationships between 〈span〉 〈span〉\(f_{\text{HVSR}}\)〈/span〉 〈/span〉 and 〈span〉 〈span〉\(h\)〈/span〉 〈/span〉. The aim of this part is to highlight the practical limitations of these established relationships and to make fair comparisons. The second is to generate new relationships, taking advantage of the very wide range of available lithological, geophysical, and geotechnical borehole drilling data of the 697 KiK-NET seismic stations in Japan. For this purpose, HVSR are calculated using 10,000 weak earthquakes or linear events recorded at KiK-NET stations to determine the 〈span〉 〈span〉\(f_{\text{HVSR}}\)〈/span〉 〈/span〉 and correlate it with the corresponding 〈span〉 〈span〉\(h\)〈/span〉 〈/span〉. The overlying layers/bedrock interface falling within sedimentary, igneous, or metamorphic layers significantly affect the derived frequency–depth relationships. In addition, these relationships are strongly reproduced by the 〈span〉 〈span〉\(V_{\text{p}} /V_{\text{s}}\)〈/span〉 〈/span〉 ratio of the bedrock in the range of 1.6–2.2. Interestingly, it is found that 〈span〉 〈span〉\(f_{\text{HVSR}}\)〈/span〉 〈/span〉 less than 1 Hz corresponding to 〈span〉 〈span〉\(h\)〈/span〉 〈/span〉 more than 100 m leads the trend of the overall frequency–depth relationship.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉On September 28, 2018, a large earthquake and its accompanying tsunami waves caused severe damage to the coastal area of Palu Bay, in the central western part of Sulawesi Island, Indonesia. To clarify the distribution of tsunami inundation and run-up heights, and damage to coastal communities due to the tsunami, the authors conducted a field survey 1 month after the event. In the inner part of Palu Bay tsunami inundation and run-up heights of more than 4 m were measured at many locations, and severe damage by the tsunami to coastal low-lying settlements was observed. In the areas to the north of the bay and around its entrance the tsunami inundation and run-up heights were lower than in the inner part of the bay. The tsunami inundation distance depended on the topographical features of coastal areas. The southern shore of the bay experienced a longer inundation distance than other shores, though generally severe damage to houses was limited to within around 200 m from the shoreline. The main lessons that can be learnt from the present event are also discussed.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We consider a transformation of long linear waves in an ocean with a variable depth. We calculate the transformation coefficients (the coefficients of transmission and reflection) as the functions of frequency and the total depth drop for three typical models of bottom profile variation: (i) piecewise-linear, (ii) piecewise-quadratic, and (iii) hyperbolic tangent profiles. For all these cases, exact solutions are obtained, analysed and graphically illustrated. This allows us to derive the transformation coefficients in the analytic form for the subsequent comparison with the results of approximate, numerical, or experimental study. We show that the results obtained are in agreement with both the energy flux conservation and Lamb’s formulae in the limiting case of zero frequency. We also study wave transformation on the underwater barriers and trenches of different shapes and compare the results obtained.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉On July 1, 2009, a 〈em〉M〈/em〉〈sub〉w〈/sub〉 6.45 earthquake ruptured south of Crete Island (Greece) along the Hellenic Arc triggering a local tsunami. Eyewitness reported the tsunami from Myrtos and Arvi (south-eastern Crete) and from the north of Chrisi Islet, located to the southeast of Crete. The earthquake occurred offshore, about 80 km south of Crete, where routine earthquake locations are poor. The hypocentre is relocated using a 2-D velocity model and several local 1-D velocity models. Epicentral locations obtained by using the different velocity models show very minor variations. Instead, relocated hypocentres can be grouped into two sets of solutions: (1) those with a shallower depth (depth 〈 12 km) obtained with the 2-D velocity model and the 1-D velocity models having a shallower Moho at less than 30 km, and (2) those with a larger depth (depth of 28 and 40 km) obtained with the velocity models having a Moho at about 40 km. Shallower hypocentres are more consistent with the tsunamigenic nature of the earthquake as also supported by tsunami numerical simulations. In fact, shallow sources (depths 〈 12 km) are capable of generating tsunami waves, while it is not the case for deeper sources (depth 〉 25 km) either in the upper-plate or along the plate interface. Models accounting for either homogeneous or heterogeneous slip on the causative fault are tested, with the heterogeneous one better reproducing the observations in terms of number of tsunami waves reaching the shoreline and duration of the sea disturbance. The short travel time, about 10 min, of the first tsunami arrival at the southern coast of Crete represents a big challenge for tsunami early warning systems operating in the area.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Rapid finite fault source determination is critical for reliable and robust tsunami early warnings. Near-field Global Navigation Satellite System (GNSS) observations have shown value to constrain the source inversion, but real-time GNSS stations are sparse along most of the active faults. Here we propose an automatic earthquake finite source inversion (AutoQuake Inversion) algorithm jointly using near-field (epicentral distance 〈 1000 km) GNSS data and mid-range (epicentral distance from 30° to 45°) teleseismic P displacement waveforms. Neither the near-field GNSS nor the mid-range teleseismic data clip or saturate during large earthquakes, while the fast-traveling P-waves are still essential to constrain the source in regions where very few or no GNSS stations are available. Real-time determination of the fault geometry remains to be the main challenge for rapid finite source inversion. We adopt a strategy to use the pre-defined geometry Slab2 for earthquakes within it or to forecast a focal mechanism based on near-by historical events for earthquakes without Slab2 prior. The algorithm has been implemented successfully in the prototype of JPL’s GPS-Aided Tsunami Early-Detection system and tested for many real events recently. This article provides the framework of the algorithm, documents the retrospective and real-time results, and discusses remaining challenges for future improvements.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The accurate measurement of ultrasonic velocity requires the detected waveforms to have a high signal-to-noise ratio (SNR). Coded excitation technique (CET) can improve the SNR without resolution loss. This study introduces the basic principles of phase-coded technology and gives a synthetic and experimental evaluation of Barker and Golay codes. All the results show that CET can increase the SNR, but the gain in SNR (GSNR) is lower than the theoretical value. The velocity measurements on red sandstone and granite verify that the Barker code has better pulse compression performance than the Golay code. Besides, the application of Barker-coded signals on the velocity monitoring of uniaxially compressed rock proves that the Barker CET is reliable.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We would like to test the concept that induced seismicity prior to relatively large mining tremor (M〈sub〉L〈/sub〉 〉 2.5, E 〉 10〈sup〉6〈/sup〉J) can be inferred from the cumulative Benioff strain release (BSR) as power law time-to-failure before the strong event. This study presents the application of accelerating BSR prior to a large earthquake, widely used in natural seismicity, for analysis of this phenomenon in induced seismicity. The Benioff strain release is quantified as accelerated releases of cumulative (square root sum) of seismic energy in the time series. During the study, five sequences were extracted from the seismic catalogues from two Polish hard coal mines: exhausted Bobrek Mine (data form the IS-EPOS Platform) and from a mine belonging to the Polish Mining Group. Next, a search radius was used to select precursory events and to indicate the type of processes occurring in the coal seam and its vicinity. The fitted power law of cumulative Benioff strain release showed changes of 〈em〉m〈/em〉-parameter. If the value of 〈em〉m〈/em〉 was lower than 1.0, the process was regarded as an accelerating-like and if 〈em〉m〈/em〉 was higher than 1.0—as a quiescence-like. The investigation of 〈em〉m〈/em〉-parameter vs. the search radius showed the general behaviour of the rock mass in the studied areas and allowed to evaluate the relationship between the critical radius and magnitude of the target event. The obtained scaling relation log(〈em〉Rc〈/em〉) ~ 0.35 M〈sub〉L〈/sub〉 is similar to these reported by other authors who analysed natural seismicity which might suggest that the scaling relation works in a wide range of magnitudes.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Iran is located in one of the Earth’s dry belts. Subtropical high-pressure and inland deserts have created arid and semiarid conditions for about 75% of the country’s area. In addition to this natural dryness, recent global climate change has also affected precipitation in different parts of Iran in terms of both mean and extreme amounts. Precipitation extremes can have many negative effects on different parts of the Earth’s ecosystems. The possible pattern of precipitation trends during recent years merits further study given the potentially important impacts on agriculture and water resources in Iran. Globally, observations show significant changes in the characteristics of extreme precipitation. To study recent trends in mean and extreme precipitation events in Iran, we examined a number of mean and extreme precipitation indices for a 58-year period (1960–2017) for 33 synoptic stations throughout the country. Daily precipitation data were collected from the Iranian Meteorological Organization for this period for all stations. Nine precipitation-based indices (one mean and eight extreme) were employed to study precipitation trends. The results showed that most areas have undergone a significant increasing trend in extreme precipitation values, precipitation intensity, and precipitation frequency. Significant positive trends were seen in the southwestern regions of Iran and the coasts of the Persian Gulf for the same precipitation indices. The results of this study could be used by managers and experts for long-term planning.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Unique observational features of a convective cluster, occurred on 12-Sept-2015, over the rain shadow region in the leeward side of Western Ghats have been presented in this study. The synoptic environment had preconditioned the formation of a convergence zone over the study area. Moisture transport from the Arabian Sea was responsible for the moistening in the lower layers. Boundary layer convective thermals contributed to middle level moistening and subsequent onset of the cloud cluster was accompanied by a sudden surge of moist and warm air into the middle troposphere, and subsequent lifting of freezing level (FL) and wet bulb temperature zero (WBT〈sub〉0〈/sub〉) levels. Sudden changes in the FL and WBT〈sub〉0〈/sub〉 levels in association with the gust front prior to the initiation of the cloud system has been documented with high-resolution measurements using microwave radiometer and wind profiler. Thermodynamical parameters from radiometer illustrate the percussive conditions for formation of the cloud system. The cloud cluster had resulted in 25.50 mm rainfall, attributing to ~ 91% of convective rain. Intense fall velocity (10–12 ms〈sup〉−1〈/sup〉) was noted up to ~ 7 km during the convective rain and the fall velocity was reduced to ~ 7 ms〈sup〉−1〈/sup〉 (below the melting layer) during the stratiform counterpart. The cloud system was forecasted using WRF model (version 3.6.1), which was reproduced reasonably well as in the observations and the model output has been analyzed to understand the morphology of the system. The features such as formation of a cold pool, initiation of convective rainfall from the system were well forecasted by the model. Microphysical characteristics of the cloud cluster have also been examined. Riming was the dominant microphysical process within the convective regime. A major contribution to precipitation was from melting of ice hydrometeors especially graupel and snow was noted. Deep warm layer and associated production of supercooled liquid by the lifting of liquid water above the freezing level in updrafts exceeding 15 ms〈sup〉−1〈/sup〉 was important for the production of a mixed-phase cloud system. Vapor deposition and aggregation process was noted in the stratiform/anvil counterpart, which also contained mixed phase hydrometeors, primarily of snow.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We present a cost-effective method for model calibration and solution of source inversion problems in atmospheric dispersion modelling. We use Gaussian process emulations of atmospheric dispersion models within a Bayesian framework for solution of inverse problems. The model and source parameters are treated as unknowns and we obtain point estimates and approximation of uncertainties for sources while simultaneously calibrating the forward model. The method is validated in the context of an industrial case study involving emissions from a smelting operation for which cumulative monthly measurements of zinc particulate depositions are available.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Three-dimensional (3D) ground-penetrating radar (GPR) systems and 3D seismic imaging techniques have been developing fast and evolving rapidly in the last decade. Ray-based migration methods have been successfully applied to processing 3D GPR signals based on the similarity between electromagnetic and seismic waves. However, reverse time migration (RTM) of 3D GPR signals has not been well studied in the past. In this paper, we present a 3D RTM based on Maxwell’s equations for 3D GPR surveys. Migration recovers the true subsurface structure from a distorted and unfocused time profile and suppresses common electromagnetic clutter and noise. RTM based on Maxwell’s equations can consider conductivity directly and compensate for the attenuation within a high-conductivity zone. Compared with 2D RTM, 3D RTM back-propagates both in-line and cross-line signals simultaneously and can include complex 3D permittivity and conductivity models. We have integrated a parallel finite-difference time-domain (FDTD) algorithm based on a hybrid MPI and OpenMP scheme to reduce the computational cost of 3D problems. The 3D RTM experiments on an anomaly of “EM” shape and a realistic sand dune model demonstrate the effective recovery of 3D subsurface structures.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The MyShake Platform is an operational framework to provide earthquake early warning (EEW) to people in earthquake-prone regions. It is unique among approaches to EEW as it is built on existing smartphone technology to both detect earthquakes and issue warnings. It therefore has the potential to provide EEW wherever there are smartphones, and there are now smartphones wherever there are people. The MyShake framework can also integrate other sources of alerts and deliver them to users, as well and delivering its alerts through other channels as needed. The MyShake Platform builds on experience from the first 3 years of MyShake operation. Over 300,000 people around the globe have downloaded the MyShake app and participated in this citizen science project to detect earthquakes and provide seismic waveforms for research. These operations have shown that earthquakes can be detected, located, and the magnitude estimated ~ 5 to 7 s after the origin time, and alerts can be delivered to smartphones in ~ 1 to 5 s. A human-centered design process produced key insights to the needs of users that have been incorporated into MyShake2.0 which is being release for Android and iOS devices in June 2019. MyShake2.0 will also deliver EEW alerts, initially in California and hopes to expand service to other regions.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉A retrospective analysis of 17 years of NCMRWF Global Forecast System (NGFS) data was conducted to understand the state and variability of cold wave episodes over northwest India. During the 2000–2016 period, a total of 21 cold wave episodes (202 cold nights) were detected, out of which 5 severe cold episodes (63 cold nights) were registered. The 10 (6) episodes occurred during La Niña (El Niño) years suggesting that both phases of El Niño-Southern Oscillation provide a favourable background for the occurrence of cold waves. The average duration of a cold wave episode was ~ 9.6 days, with the longest (shortest) episode, seen in the year 2008 (2006), lasting for 26 (6) consecutive days. The average duration of a severe cold wave episode is ≈ 4 days longer than that of a normal cold wave. In the year 2005, both the earliest (11 December) and latest (16 February) onsets of cold waves were seen. The omnipresence of intense Siberian anticyclone and the presence of western disturbance brought cold winds to the study region. Also, temperature advection and geo-potential height anomalies play vital roles in the maintenance of cold waves. The cold waves exhibit a significant intra-annual variability over northwest India. The intensity of cold waves has shown an increase of 0.11 °C per cold episode.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉When surface waves are used to characterize soils under a pavement, their presence causes problems during the analysis of the signals due mainly to the presence of Lamb waves and higher Rayleigh-wave modes in the signals. Recent studies have shown that these problems can be mitigated if the seismic source is placed on the surface of the soil while leaving the receivers on the pavement. However, the presence of a pavement at the surface of the soil does influence the propagation of Rayleigh waves even if it does not prevent its characterization. We show how we utilized the generalized S transform and the multi-modal analysis of surface waves to identify and separate the different Rayleigh-wave modes. Using 3D numerical models and experimental models, we show that the thickness of the pavement affects the energy distribution of the different Rayleigh-wave modes and that increasing the pavement thickness increases the chances of mode misidentification problems since the energy of the waves tend to travel on higher modes. We also demonstrate that for an underground profile of a given depth, the thickness of the soil layer has more importance than the thickness of the pavement on the Rayleigh-wave propagation energy and velocity. The influence of the pavement on the group and phase velocities of the fundamental Rayleigh-wave propagation mode is also shown to depend on their frequency (wavelength). We present two case studies at the end of the manuscript to confirm the conclusions established based on numerical and experimental models.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The 2016 Kumamoto earthquake occurred on April 16, 2016, and induced the complex distribution of surface ruptures and fault displacements, which revealed the difficulty of evaluating off-fault displacement hazards. The evaluation of off-fault displacements is necessary for the site investigation of an important facility, such as nuclear installations, but is difficult because off-fault displacements are thought to occur on unmapped or small-scale structures. A probabilistic fault displacement hazard analysis (PFDHA) assesses an off-fault displacement hazard as well as an on-fault one. Several PFDHA models have been developed from fault displacement datasets parsed by global-specific and Japanese-various faulting types. We developed a procedure to assess off-fault displacement hazards based on probabilistic and numerical simulation approaches. In the probabilistic approach, we constructed strike-slip and reverse-slip PFDHA models from a dataset of Japanese fault displacements. The off-fault components in PFDHA had a probability of non-zero off-fault displacement and an attenuation relationship. In the case of evaluating the site of an important facility, detailed field surveys were performed to collect numerous site-specific information. There is little site-specific data of off-fault displacements in Japan. The trench surveys were performed at off-fault displacement sites from the 2016 Kumamoto earthquake. The two trench sites were selected based on a linear low-coherence zone derived from the InSAR analysis, which emphasizes small-scale displacements. The excavation survey result at one site suggests a shorter recurrence interval than that of the active fault long-term evaluation. We also performed a probabilistic fault hazard analysis (PFDHA) of the trench sites by using the global strike-slip model and Japanese PFDHA models with and without the site-specific data. For the PFDHA results without site-specific data, the difference in the annual rates of exceedance between the global strike-slip and Japanese models increased with increasing fault displacements. This is because of the reduced decrease in the attenuation relationship of Japanese models. The differences in the annual rates of exceedance constrained with the site-specific data are independent of fault displacements due to variation in the probability of non-zero off-fault displacement between the global strike-slip and Japanese PFDHA models. These results suggest that the off-fault PFDHA models have high variability. In the case of PFDHA evaluation with several models, the individual PFDHA components are carefully selected by considering the individual effects. The site-specific short recurrence interval revealed by the trench survey leads to higher annual rates of exceedance.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉This study characterizes different rainfall types using surface-based instruments (i.e. micro rain radar and laser precipitation monitor) installed at the Indian Institute of Technology Bhubaneswar Jatani, Odisha, India. A total of twelve rainfall cases including four from each season, i.e. pre-monsoon, monsoon and post-monsoon, are considered. The segregation of rainfall is carried out using radar reflectivity and rainfall intensity. In general, initial rainfall is dominantly convective and followed by a stratiform type. Two distinct maxima of radar reflectivity are noted at 3 and 5 km, suggesting the presence of high liquid water content and a melting band. The presence of liquid water content suggests occurrence of a warm rain process with shallow, intense convective cores. Results indicate a higher drop number density below 2 km with smaller size drops for convective rainfall and vice versa for the stratiform rainfall. Furthermore, 〈em〉Z〈/em〉–〈em〉R〈/em〉 relationships are computed for all the cases using a linear regression method, and the results suggest that the stratiform rainfall shows a higher slope parameter and lower intercept parameter as compared to convective rainfall. The distribution of drop number density shows a mono-modal and bimodal pattern for convective and stratiform rainfall, respectively.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Soil gas radon concentrations were continuously monitored from November 2016 to May 2018, close to an active fault zone in the area of Ioannina (Northwestern Greece) that gave rise to intense seismic swarms with magnitudes up to 5.3 on the Richter scale, during October 2016. Meteorologic parameters (soil and air temperature, atmospheric pressure, wind speed and rainfall) were simultaneously obtained, and their contribution to radon fluctuations was examined by partial correlation and cross-correlation analysis. Soil temperature and atmospheric pressure were found to be the parameters controlling radon concentrations, and their effect was reduced using multiple linear regression analysis. During the monitoring period, 11 spike-like anomalies were identified in the residual radon time series using the 2〈em〉σ〈/em〉 deviation criterion. The duration of the anomalies varied from 〈 1 day to approximately 5 days. Earthquakes of local magnitudes 〈em〉M〈/em〉〈sub〉L〈/sub〉 〉 2.5, occurring within a distance of 100 km from the monitoring site, were collected and filtered by applying Dobrovolsky’s radius approach. Most of the observed radon anomalies were likely associated with seismic events, and the precursor time ranged roughly from 2 to 15 days.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The Eurasia–Nubia plate boundary between the Azores and the Strait of Gibraltar has been the place of large tsunamigenic earthquakes. The tectonic regime is extensional in the Azores, transcurrent along the Gloria Fault, and compressional in the Strait of Gibraltar. Here, the plate boundary is not clearly defined. The knowledge of past events that occurred in the area constitutes an essential contribution to the evaluations of seismic and tsunami hazard in the North-East Atlantic. In this study, we present an overview of the six major events in the area and show the use of tsunami data to add some constraints on their source. The historical events occurred in the eighteenth-century between 1722 and 1761, while the twentieth-century events occurred between 1941 and 1975. We speculate that major tsunamigenic earthquakes that occur in the Iberia-Maghreb area take place at the boundaries of a lithospheric block approximately defined by the location the six events summarized here, which role and dynamics are not yet understood.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In the numerical simulation of induced seismicity, much attention is generally paid to the calibration of the frictional resistance of the causative fault to obtain a seismic moment consistent with that of the actual event, whereas sufficient investigation is not made in the estimation of the slip-weakening distance 〈em〉D〈/em〉〈sub〉c〈/sub〉 as well as in the calibration of seismically radiated energy. The present study addresses this problem by numerically and analytically investigating the relation between 〈em〉D〈/em〉〈sub〉c〈/sub〉 and seismic source parameters. First, this study performs the dynamic simulation of an induced seismic event caused by a decrease in the effective normal stress. The analysis demonstrated that seismic efficiency 〈em〉η〈/em〉 can be used to improve the accuracy of estimating the critical slip-weakening distance and the coefficient of kinetic friction 〈em〉µ〈/em〉〈sub〉d〈/sub〉 whilst considering not only seismic moment but also radiated energy in the calibration. This gave insight into the development of the new calibration method for induced seismicity that considers energy-related seismic source parameters. Furthermore, a new scaling law of the slip-weakening distance was derived from the theoretical expression of seismic efficiency 〈em〉η〈/em〉, considering seismic moment 〈em〉M〈/em〉〈sub〉o〈/sub〉 and scaled energy 〈span〉 〈span〉\( \hat{e} \)〈/span〉 〈/span〉. The proposed scaling law can yield the relation between 〈em〉D〈/em〉〈sub〉c〈/sub〉 and 〈em〉M〈/em〉〈sub〉o〈/sub〉, which is shown to be similar to that obtained from a previous study, but additionally considers the relation between seismically radiated energy and 〈em〉D〈/em〉〈sub〉c〈/sub〉. The dependency of 〈em〉D〈/em〉〈sub〉c〈/sub〉 on seismically radiated energy implied from the proposed scaling law has been verified from the dynamic analyses where 〈em〉η〈/em〉 = 0.06 was used to place a constraint on 〈em〉D〈/em〉〈sub〉c〈/sub〉 for seismic events with different magnitudes. The developed numerical simulation methodology of induced seismicity as well as the scaling law considering the energy indices significantly contributes to improving the accuracy of back-analysis, thus leading to a more accurate estimation of the mechanical properties of faults and/or shear zones in seismically active regions of deep underground mines or reservoirs composed of discontinuous hard rock masses.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉This paper starts with reviewing the basis of civil and mechanical engineering practices, focusing on the need for engineers to know the maximum effects induced by applied loads, including seismic loads. In this context, the response spectrum appeared historically as the most convenient tool for representing the seismic input motion; especially in design standards. Pro and cons of this model are discussed, with an emphasis on industrial facilities, for which two major difficulties appear, for transferring the input motion through the supporting structure towards the equipment and generating realistic input motions when necessary for the analysis of cases with inherent non-linear response. Another option advocated in this paper is that a power spectral density format is used for seismic input motion modelling. Outlines of the approach are presented as well as candidate input motion; its pro and cons are discussed. Compared to the response spectrum, the method simplifies dramatically the generation of compatible time series and the calculation/computation of seismic motion transferred to equipment. It makes easy the calculation of seismically induced fatigue type damage. Calculation of the maximum of the response is less straightforward than with the response spectrum, but the case is resolved by using peak factors.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We analytically solve the nonlinear shallow water theory for the tsunami run-up on a plane beach in the presence of tide and show that over a plane beach the tide in the nearshore zone can be considered static (uniform in space and frozen in time). With this assumption, we find an exact analytical solution for the tsunami run-up height as a function of the amplitude of the incident wave and analyse the influence of the tide on the tsunami run-up characteristics. We confirm these results by calculation of the total tsunami and tidal run-up field using analytical solutions of the initial nonlinear shallow water equations.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉〈em〉Pure and Applied Geophysics〈/em〉 (PAGEOPH) is one of the leading journals in the field of geophysics. The first issue was published in 1939; thus, the journal is celebrating its 80th anniversary in 2018. The aim of this paper is to provide a complete lifetime overview of the academic structure of the journal using bibliometric indicators. This analysis includes key factors such as the most cited articles, leading authors, originating institutions and countries, publication and citation structures, and the most commonly used keywords. The bibliometric data used to conduct this analysis comes from the Scopus database. Additionally, the visualization of similarities (VOS)viewer software is used to create a graphic map of some of the bibliometric results. The graphical analysis uses co-citation, bibliographic coupling and co-occurrence of keywords. The results indicate that PAGEOPH is a leading journal in the areas in which it is indexed, with publications from a wide range of authors, institutions, and countries around the world.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The goal of this study is to explore the chaotic behavior of sea surface temperature (SST) in the Indian Ocean and in the equatorial Pacific Ocean. The SST time series is analyzed for Bay of Bengal, Arabian Sea and South Indian Ocean as well as for two extreme phenomena: El Niño and Indian Ocean Dipole (IOD). The analysis is based on Singular spectrum analysis, and singular value decomposition (SVD). Our analysis reveals that the dynamics of SST is chaotic in varying degrees in all the studied cases, since Lyapunov exponent, an indicator of chaoticity, is positive in each case. To study the degree of predictability of these SST series, we search for embedded periodic component(s) using two different approaches: Orthogonal functions extracted from the Singular spectrum analysis and Periodicity spectrum analysis based on SVD. Both the methods reveal presence of a strong periodic component(s) for the SST signals in the Arabian Sea, Bay of Bengal and South Indian Ocean, whereas no periodicity is found for El Niño and IOD. Therefore, it can be concluded that the dynamics of SST is more complex in the El Niño and IOD region compared to Bay of Bengal, Arabian Sea and South Indian Ocean; hence it is much more difficult to predict El Niño and IOD.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The study evaluates the Indian summer monsoon prediction skill of the Atmospheric General Circulation Model (AGCM) and the impact of sea surface temperature (SST) boundary forcing on the model performance. The National Center for Environmental Prediction's (NCEP's) T170/L42 AGCM model configured with a horizontal resolution of 75 × 75 km, with 42 vertical levels is used for the study. The SST-rainfall relationship is examined in the coupled Climate Forecast System version 2 (CFSv2) model, as CFSv2-predicted SST is used as input for the T170 model. The NCEP Global Forecast System-T170 (GFS-T170) simulations are carried out with boundary forcing of observed SST, CFSv2-predicted SST and the bias-corrected CFSv2 SST. An ensemble of seasonal runs was made using the initial conditions of May to September, and integrated up to September 30th. The significance of discontinuity in the initial conditions due to climate forecast system reanalysis (CFSR) is assessed based on the two-period approach of climatology for the two time scales of 1985–1998 and 1998–2009. CFSv2 predicted climatological summer monsoon rainfall with a significant dry bias over the three convection zones; Western Ghats, Central India and North-east India, and cold bias over the Indian ocean basin and central equatorial Pacific, with strong cold bias over a narrow region of equatorial Pacific. The model could capture 64% (16 out of 25) of the year’s rainfall anomaly signal. The skill of the model is improved in the recent period (1999–2009). The model could simulate the negative Nino 3 and excess rainfall and the La Nina event realistically for the year 1988. The model shows a large difference in Nino indices for the years 1987 and 1998, which led to the unrealistic rainfall simulation. The model has a low skill for indicating the relationship between the Indian Ocean Dipole (IOD) and Indian summer monsoon rainfall (ISMR). The CFSv2 model could not capture the strong positive correlation of the IOD and strong negative correlation of Nino 3 with the ISMR for the period 1999–2009 realistically, suggesting improvement of SST simulation in the CFSv2 model. The T170 model forced with observed SST shows wet bias in peninsular India and dry bias over North-east India, whereas that of CFSv2-predicted SST simulated a wet bias in peninsular India and widespread dry bias in North and Central India. When the model was forced with bias-corrected CFSv2 SST, the dry bias improved in North and Central India, and the intensity of wet bias increased in peninsular India. The model could capture 56, 48 and 64% of the year’s rainfall anomaly signal (positive or negative) correctly in the same sign for being forced with observed SST, CFSv2-predicted SST, and bias-corrected CFSv2 SST, respectively.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We analyze waveform-relocated seismicity (1981–2016) and other geophysical and geological datasets from 16 lithotectonic crustal blocks in southern California. We explore how earthquake depth histograms (EDH) are related to crustal strength, lithology, and temperature of the crust. First, we calculate relative EDHs to quantify the depth distribution of seismicity for each lithotectonic block. Second, we calculate depth profiles of maximum differential stress (“yield strength envelopes”, YSEs) using Byerlee’s law and a non-linear dislocation creep law. We use observed average heat flow values, strain rates, and states of stress to parameterize YSEs for five different crustal candidate lithologies in each lithotectonic block. We assume that seismicity ceases where the mechanical rock strength falls below a critical threshold level, and identify the YSE that best predicts the depth extent of seismicity in each block. The lithologies of the best matching YSEs are found to agree well with expectations from past tectonics: they are mostly quartz-dominated except for the feldspar-rich diorite lithologies in the Great Valley, the southernmost western Sierra Nevada, Inner Continental Borderland, and Rifted crust in the Salton Trough. Similarly, the inferred thermo-mechanical properties, including differential stress, lithology, and geotherms reflect the previously mapped tectonic variability between the 16 lithotectonic blocks. On average, the differential yield stress is smaller and peaks at a shallower depth in hotter and more quartz rich crust but is larger and peaks at greater depths for colder and predominantly diorite crust. The good agreement between the modeled YSEs, the EDHs and tectonic considerations suggests that EDHs indeed reflect long-term geophysical properties of the crust and can be used to infer thermo-mechanical properties at depth. In contrast, shallow seismicity may be more likely to reflect short-term strain transients from fluid flow or recent anthropogenic disturbances.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉It is well known that high impedance contrasts between salt bodies and their surroundings yield blurriness in seismic images which does not allow adequate interpretation; some of the artifacts generated by this process are multiple reflections and diffractions. In this work we propose a novel method of detection and attenuation of multiples from seismic gathers which is based on pattern recognition and fuzzy logic. In order to corroborate the effectiveness of this new approach, we use synthetic models which mimic a region intensely affected by salt tectonics in deep-water Gulf of Mexico. We obtained synthetic seismic sections by simulating wave propagation with an FDTD–CPML formulation. Detection of seismic events is performed through the mapping of parabolic shapes in shot gathers that approximate the recorded wavefronts. Undesired multiple events are then surgically attenuated by using fuzzy threshold criteria. Results show an optimal attenuation of multiple events, even when they are not directly related to salt structures.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Evapotranspiration can be considered as an indicator in evaluating the effects of climate change. It is the sole factor with the capability of concurrently balancing the ecosystem energy and water fluxes. Reference evapotranspiration (ETo) is the amount of water evaporated from reference crop that is affected by climatic parameters. The aim of this study was to assess ETo during the period of 2020–2049 in various climatic zones of Iran (including Tabriz, Bushehr, Isfahan, Sanandaj and Urmia). Climatic parameters including relative humidity, wind speed, Sunshine hours, atmospheric pressure, maximum and minimum temperatures were utilized for calculating ETo using FAO Penman–Monteith equation. The NCEP data and HADCM3 model data (under scenario A2 and B2) were used for prediction of future climatic parameters during 2020–2049. Statistical down scaling model was used as a hybrid regression model as well as a stochastic weather data generator. The course period was between 1986 and 2015 that was regarded for calibration and evaluation of the model. Subsequently, evapotranspiration was estimated using the model outputs in the FAO Penman–Monteith equation. Results indicated that the simulated data by the model has the same accuracy and validity under both scenarios A2 and B2. Results showed that in the studied areas, ETo tend to have an increasing trend in upcoming years. In scenario A2, ETo will increase about 16.81, 0.137, 17.52, 9.46 and 2.57 mm year〈sup〉−1〈/sup〉 in Tabriz, Bushehr, Isfahan, Sanandaj and Urmia stations, respectively. Also our results represented that ETo will increase about 7.67, 6.52, 10.33, 7.73 and 1.99 mm year〈sup〉−1〈/sup〉 in Tabriz, Bushehr, Isfahan, Sanandaj and Urmia stations, respectively based on the B2 scenario. Although no significant trend was observed in most of the climatic variables under A2 and B2 scenarios over the time period of 2020–2049, the ETo significantly increased during this period. Hence it could be concluded that ETo is a better indicator for describing the future climate change, compared to other climatic variables.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We analyze the background stress field around the San Jacinto fault zone (SJFZ) in Southern California with a refined inversion methodology using declustered focal mechanisms of background seismicity. Stress inversions applied to the entire fault zone, and three focus areas with high level of seismicity, provide three-dimensional distributions of the maximum horizontal compression direction (〈em〉S〈/em〉〈sub〉Hmax〈/sub〉), principal stress plunges, and stress ratio 〈span〉 〈span〉\(R = (\sigma_{1} - \sigma_{2} )/(\sigma_{1} - \sigma_{3} )\)〈/span〉 〈/span〉. The results are compared with coseismic strain parameters derived from direct summation of earthquake potencies and 〈em〉b〈/em〉 values of frequency–size event statistics. The main stress regime of the SJFZ is strike-slip, although the northwest portion near Crafton Hills displays significant transtension. The 〈em〉S〈/em〉〈sub〉Hmax〈/sub〉 orientation rotates clockwise with increasing depth, with the largest rotation (23°) observed near Crafton Hills. The principal stress plunges have large rotations below ~ 9 km, near the depth section with highest seismicity rates and inferred brittle–ductile transition zone. The rotations produce significant deviations from Andersonian strike-slip faulting, likely generating the observed increased dip-slip faulting of relatively deep small events. The stress ratio parameters and 〈em〉b〈/em〉 value results are consistent with increasing number of dip-slip faulting below ~ 9 km. The derived coseismic strain parameters are in good agreement with the stress inversion results. No large-scale stress rotations are observed across the time of the 2010 〈em〉M〈/em〉〈sub〉w〈/sub〉 7.2 El Mayor–Cucapah earthquake. The stress ratio near the Trifurcation area of the SJFZ changes after the El Mayor–Cucapah earthquake toward transpression, but this may have been produced by local 〈em〉M〈/em〉 〉 5.4 event or aseismic slip.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The variability in nearshore wave climate of the eastern part of the Black Sea was studied based on 38 years of wave hindcast data from spectral wave modelling for the period from 1979 to 2016. Correlation analysis has revealed the spatial inhomogeneity within the region on the short timescale from a few hours to one day, with the southern part being more homogeneous than the northern one. The variability of annual mean wave heights in these two regions were compared using wavelet correlation analysis. The wave climate variability at four chosen locations subject to wave modelling was correlated with climate indices (NAO, AO, AMO, PDO and EA/WR) on the following timescales: 20–30, 10–17 and 4–7 years. Despite the fact that the selected periods of fluctuations of average annual wave heights are almost the same for the chosen locations due to changes in climatic indices, a decrease or increase in amplitudes of the same frequency (multi-annual and decennial) can occur in antiphase even within the same coast. Such behavior is probably caused by complex inhomogeneous wind conditions near the coast. Fluctuations of annual mean wave heights of southern and northern coasts correlate with teleconnection patterns in antiphase on multi-decadal periods of about 20–30 years. To conclude, the nearshore wave climate variability of the eastern part of the Black Sea is inhomogeneous and therefore it can be divided at least into three regions: northeastern, northwestern and southern.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉This paper concerns the problem of predicting the maximum expected earthquake magnitude 〈span〉 〈span〉\(\mu\)〈/span〉 〈/span〉 in a future time interval 〈span〉 〈span〉\(T_{\text{f}}\)〈/span〉 〈/span〉 given a catalog covering a time period 〈span〉 〈span〉\(T\)〈/span〉 〈/span〉 in the past. Different studies show the divergence of the confidence interval of the maximum possible earthquake magnitude 〈span〉 〈span〉\(m_{ \hbox{max} }\)〈/span〉 〈/span〉 for high levels of confidence (Salamat et al. 〈span〉2017〈/span〉). Therefore, 〈span〉 〈span〉\(m_{ \hbox{max} }\)〈/span〉 〈/span〉 should be better replaced by 〈span〉 〈span〉\(\mu\)〈/span〉 〈/span〉 (Holschneider et al. 〈span〉2011〈/span〉). In a previous study (Salamat et al. 〈span〉2018〈/span〉), 〈span〉 〈span〉\(\mu\)〈/span〉 〈/span〉 is estimated for an instrumental earthquake catalog of Iran from 1900 onwards with a constant level of completeness 〈span〉 〈span〉\(\left( {m_{0} = 5.5} \right)\)〈/span〉 〈/span〉. In the current study, the Bayesian methodology developed by Zöller et al. (〈span〉2014〈/span〉, 〈span〉2015〈/span〉) is applied for the purpose of predicting 〈span〉 〈span〉\(\mu\)〈/span〉 〈/span〉 based on the catalog consisting of both historical and instrumental parts. The catalog is first subdivided into six subcatalogs corresponding to six seismotectonic zones, and each of those zone catalogs is subsequently subdivided according to changes in completeness level and magnitude uncertainty. For this, broad and small error distributions are considered for historical and instrumental earthquakes, respectively. We assume that earthquakes follow a Poisson process in time and Gutenberg–Richter law in the magnitude domain with a priori unknown 〈span〉 〈span〉\(a\)〈/span〉 〈/span〉 and 〈em〉b〈/em〉 values which are first estimated by Bayes’ theorem and subsequently used to estimate 〈span〉 〈span〉\(\mu\)〈/span〉 〈/span〉. Imposing different values of 〈span〉 〈span〉\(m_{ \hbox{max} }\)〈/span〉 〈/span〉 for different seismotectonic zones namely Alborz, Azerbaijan, Central Iran, Zagros, Kopet Dagh and Makran, the results show considerable probabilities for the occurrence of earthquakes with 〈span〉 〈span〉\(M_{w} \ge 7.5\)〈/span〉 〈/span〉 in short 〈span〉 〈span〉\(T_{\text{f}}\)〈/span〉 〈/span〉 , whereas for long 〈span〉 〈span〉\(T_{\text{f}}\)〈/span〉 〈/span〉, 〈span〉 〈span〉\(\mu\)〈/span〉 〈/span〉 is almost equal to 〈span〉 〈span〉\(m_{ \hbox{max} }\)〈/span〉 〈/span〉.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The main purpose of this study is to propose an innovative methodology to forecast the cumulative probability of future larger earthquakes for any given magnitude. It is based on applying an innovative approach to explicitly incorporate the logarithmic mean annual seismicity rate and its standard deviation, replacing the conventional Gutenberg–Richter (G–R) relation, which is only expressed by the arithmetic mean. The new representation of the G–R relation can provide the median annual seismicity rate and upper and lower bounds of recurrence time period for future larger earthquakes in different regions of Taiwan. Subsequently, the logarithmic mean is found to have a more well-behaved lognormal distribution. The selected crustal earthquake data for 3.0 ≤ 〈em〉M〈/em〉〈sub〉w〈/sub〉 ≤ 5.0 are used to obtain alternative Gutenberg–Richter relations for different regions. The results are as follows: 〈span〉 〈span〉\(\log_{10} N = 5.74 - 1.07M_{\text{w}} \pm ( - 0.18 + 0.12M_{\text{w}} )\)〈/span〉 〈/span〉 in and Taiwan; 〈span〉 〈span〉\(\log_{10} N = 5.08 - 1.07M_{\text{w}} \pm (0.23 + 0.05M_{\text{w}} )\)〈/span〉 〈/span〉 for northeastern Taiwan offshore; 〈span〉 〈span〉\(\log_{10} N = 5.48 - 0.95M_{\text{w}} \pm ( - 0.32 + 0.14M{}_{\text{w}})\)〈/span〉 〈/span〉 for eastern Taiwan offshore; 〈span〉 〈span〉\(\log_{10} N = 4.57 - 0.84M_{\text{w}} \pm (0.07 + 0.07M_{\text{w}} )\)〈/span〉 〈/span〉 for southeastern Taiwan offshore. These results can be used for preventing and mitigating seismic hazards.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The 〈em〉b〈/em〉-value is closely related to the crustal stress. By studying the 〈em〉b〈/em〉-value trends of regions before large earthquakes, we can obtain the evolution of crustal stress, which is generally considered useful earthquake precursor information. A quake is closely related to fault tectonic movement. In the past, the traditional 〈em〉b〈/em〉-value calculation method did not consider the spatial distribution of the fault. Here, we propose a new algorithm based on the fault’s buffer area, combining the spatial distribution and trend of the fault. This algorithm can accurately calculate the 〈em〉b〈/em〉-value changes for a specific fault using the fault as the basic independent unit. This method provides a useful reference for earthquake hazard judgment. Based on this algorithm, we use a total of 428,963 earthquakes from 1980 to 2013 after removal of the aftershock sequences and combine these quakes with the active fault distribution data to study the 〈em〉b〈/em〉-value changes before major earthquakes in western Sichuan. The results show that the 〈em〉b〈/em〉-values of the Fubianhe fault, Longmenshan main fault, and Shuangshi–Pengguan fault in western Sichuan decreased for at least 2 years before the earthquakes. The Longmenshan main fault area began to decrease slowly 5 years before the Wenchuan Ms8.0 earthquake and sharply decreased in the year before the quake, which reflects a significant change in crustal stress during this time. This conclusion and the method are available for long-term earthquake hazard assessment as a reference.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Fragility curve evaluation using ground motions compatible with conditional spectra allows for ground motion selection with good consistency with the hazard. However, this evaluation requires selecting ground motions from a database, which is not straightforward. Moreover, it relies on a fragility curve fitting procedure, which may fail to give a solution. Lastly, it estimates the statistical uncertainty of the curve based on simple bootstrap resampling. This paper proposes a novel framework for estimating fragility curves with two major improvements. First, the proposed fragility curve fitting procedure is not iterative and does not require an initial estimation of the curve parameters, unlike the existing curve fitting procedure. Second, the statistical uncertainty of fragility curves is estimated based on the Fisher’s information matrix, which is a rigorous alternative to bootstrap resampling. Moreover, stochastic ground motions compatible with the conditional spectra are generated and used as excitations. This is a practical alternative, as it does not require a ground motion database for scenario-specific selection. Results obtained with the developed framework are compared to results based on existing procedures in a case study of in-structure components in an industrial building. We analyze cases in which our curve fitting procedure gives a solution more reliably than the existing. Moreover, the developed procedure for estimating the uncertainty of fragility curves leads, in this case study, to better estimations for the statistical uncertainty of the fragility curves.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Based on combined data of the Global Positioning System (GPS), Global Land Data Assimilation System (GLDAS), and Gravity Recovery and Climate Experiment (GRACE), the seasonal hydrological loading over the Asian continent is characterized in this study. The hydrological loading effects over the Asian continent display strong latitude dependence. The significant hydrological loading effects appear at the GPS stations situated in the coastal areas, some regions near large rivers and lakes, and high-latitude areas in Russia, as evidenced by the fact that a large root mean square (RMS) and high percentage of the variance related to the annual signal modeled by singular spectrum analysis (SSA) for each measurement are cumulated at the stations located in these regions. In contrast, the hydrological loading effects are not pronounced in mid-latitude areas of the Asian continent (e.g., Central Asia, northern and plateau regions of China), which is due to the high topographical variability and scarce water resources in these regions. Then, the cross wavelet transform (XWT) is used to quantify the consistency between different data sets. For the data sets of GPS/GLDAS, the XWT-based semblance for 64% of the stations reaches above 0.8, while it reaches above 0.8 for 48% for the data sets of GPS/GRACE, indicating that the data sets of GPS/GLDAS present better consistency. In addition, we also discuss the effects of hydrological loading on GPS observations from the RMS value, noise characteristic, and velocity uncertainty. After applying the hydrological loading correction, the RMS values of almost all GPS observations are reduced with different amplitudes, implying that the hydrological loading correction can reduce the RMS values of most GPS observations in the Asian continent. Meanwhile, the variations of noise and velocity uncertainty suggest that hydrological loading has changed the noise characteristic of almost all GPS observations, and thus lead to the overestimation of velocity uncertainty.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The 2018 Sulawesi earthquake (Mw 7.5) and tsunami destroyed many buildings and caused more than 3300 fatalities in Sulawesi, Indonesia. Damage reports and satellite images from Palu City indicated severe tsunami impacts to buildings and lifelines infrastructure within 300 m from the coastline. Seven-weeks after the earthquake a field survey was carried out in Palu City to measure tsunami flow depths and record damage levels for buildings, roads and electricity infrastructure. Above ground level tsunami flow depths measured at 371 building sites ranged from 0.1 to 3.65 m, with a 1.05 m mean and 0.55 m standard deviation. The survey team also recorded attributes and damage levels for 463 buildings, 7.9 km of road and 455 utility poles. We observed that non-engineered ‘light timber’ and ‘lightly reinforced concrete’ construction frame buildings were highly susceptible to ‘non-structural’ component damage when tsunami flow depths respectively exceed 0.4 m and 1 m above the first finished floor level, while unrepairable or complete building damage was regularly observed when flow depths exceeded 1.2 m. Only non-structural component damage was observed for engineered ‘reinforced concrete’ buildings. While tsunami flow depth traces could not be measured for affected road and utility pole components, hazard intensity parameters can be obtained from tsunami inundation maps to estimate the conditions contributing to observed damage levels. The information presented herein forms an important evidence base to support future tsunami hazard and risk research in Indonesia.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The 〈em〉M〈/em〉〈sub〉w〈/sub〉 7.8 Kaikōura, North Canterbury, New Zealand earthquake, which occurred on 14 November 2016 (local time), was one of the most complex continental earthquakes ever documented and among the largest instrumentally recorded events in New Zealand history. The epicenter was located at the southern termination of the Hikurangi margin, where the subducting Pacific Plate transfers into the dextral Alpine transform fault. In this work, we precisely estimate three-dimensional coseismic and postseismic displacements caused by this event from continuous global navigation satellite systems (GNSS) stations in New Zealand. The Kaikōura earthquake activated significant and diverse coseismic and postseismic deformation on a large spatial scale, located mainly in the southern part of the North Island and the northern part of the South Island. Station CMBL had the largest coseismic offsets and the most remarkable postseismic displacements. The accumulated postseismic displacements at this station reached 13, 7 and 29% of the coseismic values on the east, north and vertical components, respectively, in the first 1.5 years after the mainshock. Integrating our estimated coseismic displacements with previously published coseismic displacements, we inverted for the spatial distribution of coseismic slip and spatiotemporal evolution of postseismic slip. Our optimal coseismic model suggests that rupture occurred both on shallow crustal faults, and to some extent at the southern Hikurangi subduction interface. The GPS-inverted coseismic moment release is equivalent to an 〈em〉M〈/em〉〈sub〉w〈/sub〉 7.9 event. The postseismic slip was not only significantly extended at the subduction interface, but also appeared on the Needles fault. The cumulative moment magnitude is 〈em〉M〈/em〉〈sub〉w〈/sub〉 7.35 in the first 1.5 years after the event, and 〈em〉M〈/em〉〈sub〉w〈/sub〉 7.35, 〈em〉M〈/em〉〈sub〉w〈/sub〉 6.95 and 〈em〉M〈/em〉〈sub〉w〈/sub〉 6.80 during the periods 0.0–0.5, 0.5–1.0  and 1.0–1.5 years, respectively, indicating rapid decay of the postseismic deformation. Comparing the spatial distribution of the postseismic to the coseismic slip, although their direction is similar, the discrepancy between their location is significant: the slip located along the shallow crustal faults activated the coseismic deformation, while the slip located on the deep subduction interface controlled the postseismic deformation.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Tsunamigenic earthquakes along the Alaska–Aleutian megathrust pose a major threat to many rural coastal communities in Alaska. To mitigate the impact of tsunamis and minimize loss of life, maximum potential runup and tsunami hazard zones need to be estimated despite a lack of the high-resolution digital elevation models. In this manuscript we present a methodology to approximate tsunami hazard zones in areas with poor topographic and bathymetric coverage. To manage a trade-off between the computational complexity and lack of quality data, we develop three scenario earthquakes with the intention that one of them characterizes impacts of a credible worst-case event. We then apply a safety factor to account for the limited number of considered scenarios and a coarse resolution elevation model used to simulate water dynamics near the community. The developed methodology is illustrated using a case study focused on the community of Adak, in the Andreanof Islands, Alaska. To validate the proposed method, we explore sensitivity of tsunami height with respect to the coseismic slip distribution and develop a comprehensive set of credible worst-case scenarios for the community. The tsunami hazard zone, developed with the use of the safety factor, is validated against high-resolution modeling of potential inundation according to the set of worst-case scenarios in a number of other coastal communities.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In this paper, we present a robust 2-D self-potential (SP) inversion algorithm that has proven to be suitable for both environmental and hydrogeological applications. The work proposed here continues from the recent advances in theoretical and experimental aspects of the self-potential method by detecting the depth and the shape of shallow electrical current density sources using the least square subspace preconditioned (LSQR) method to compute (an approximation to) the standard-form Tikhonov solution. The preconditioner is based on the subspace defined by the columns of the Kernel matrix and the method adopted for choosing the fixed value of the regularization parameter is the generalized cross-validation. The decrease of resolution, due to the fact that the self-potential field decays quickly with the distance, is controlled by a depth weighting matrix. A laboratory experimental setup has been assembled for locating two buried ferro-metallic bodies of any size at different depths using the inversion of self-potential signals associated with the redox process. The inverse problem is solved by accounting for the electrical conductivity distribution and the self-potential data in order to recover the source current density vector field. Both synthetic and real simulations, performed on a sand model with anomalies included, provide low-error inverted models whereas anomalies are well-detected for position and shape. The inversion algorithm has been also applied to a field data set collected in the San Vittorino Plain, located in Central Italy, in order to identify the location of sinkholes and investigate the effects of different resistivity structure assumptions on the streaming potential inversion results.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Seismic activity of Podhale (Poland) and Spiš (Slovakia) regions has been recognized for years. The first information about tremors from this area comes from the XVIII century. Four earthquakes, with intensity over VI in the MSK scale, were reported in 1643, 1724, 1840 and 1901. Since 1960’s an instrumental measurements have been conducted. However, until 2011 no stronger tremors have been recorded in the area of artificial water reservoir Czorsztyn lake located in extremely complex geotechnical condition, between border zone of Inner and Outer Carpathians separated by Pieniny Klippen Belt. Before Czorsztyn 2D seismic survey, knowledge of tectonic boundaries and velocities was very limited. The seismic survey confirmed assumptions of a flower type faults system and provided the first 3D velocity model for this area. After a series of earthquakes, in 2013 a SENTINELS network started its operation and since that time it recorded almost 200 events. The focal mechanisms were calculated for around 20 of them. Both location and moment tensor are crucial in the investigation of the origins of seismogenic process related to industrial operations. Therefore the relocation of the events and validation of the moment tensor solutions for the SENTINELS network were conducted with the use of a 3D velocity model. The validation of mechanisms was conducted with the use of the synthetic tests based on the 1D velocity model derived from the 3D velocity model, taking into account its lateral velocity anisotropy. It was based on the synthetic amplitudes generated with the assumed normal and strike-slip faulting type, similar to the obtained solutions. The validation proved that focal mechanisms are reliable even in a sparse focal coverage and noise not exceeding 40% of the P-wave amplitude. Most of the events are normal or strike-slip with nodal planes striking NW–SE or NNE-SSW. The latter ones are in agreement with the orientation of the main discontinuities in this area.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The July 20, 2017 Bodrum–Kos Earthquake caused tsunami wave motions and damage in the south of Bodrum Peninsula, Turkey, and on Kos Island, Greece. Immediately after the earthquake, we conducted several post-tsunami field surveys including interviews in coastal zones impacted by the tsunami, i.e., the coastlines of Bodrum Peninsula, Karaada Islet and Akyaka Town in Gökova Bay, Turkey, and eastern Kos Island, Greece. We present observations and measurements to document the variation of the tsunami effects along the coast. The largest tsunami runup was about 1.9 m and observed at the mouth of a small dry streambed at Gumbet Bay, Bodrum. No significant water motions were reported at the northern and western coasts of Bodrum Peninsula. The tsunami runup distribution along the coast of eastern Kos was overall regular, with runup not exceeding 1 m except in the Port of Kos where a 1.5 m tsunami runup was measured.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Earthquake lights (EQLs) have long been considered mysterious natural phenomena, for which no good physical explanation seemed to be available. Crucial to understanding EQLs, in particular the intense flashes of light bursting out of the ground while S waves propagate, is the presence of peroxy defects in igneous rocks, in particular in gabbroic rocks that typically fill the subvertical dykes in regions of past extensional tectonics. The peroxy defects tend to locate along grain boundaries or may even link adjacent mineral grains, making them highly susceptible to ever so slight displacements of mineral grains. Thus, the passage of an S wave will instantly activate peroxy bonds. If the number density of the stress-activated peroxy is so high that their delocalized wave functions overlap, the entire rock volume must instantly expand, supported from within by an electronic degeneration pressure. This process will be followed by a momentary dissociation of the peroxy defects, generating e′ and h· charge carriers, causing the volume to instantly contract again, at least partly. If an electric discharge can burst out from the top of the dyke, removing some of the charge carriers and generating an EQL, an additional volume contraction can be expected occur.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The five great trans-Pacific tsunamis of the 20th century that occurred in 1946, 1952, 1957, 1960 and 1964 were accurately recorded by analogue tide gauges on the coast of British Columbia. All available pen-and-paper records of these events were collected, digitised, de-tided and analysed. The 1946 Aleutian Islands event was recorded at two stations, Tofino and Victoria, where maximum trough-to-crest tsunami wave heights were 55 and 27 cm, respectively. These two gauged stations, as well as Prince Rupert, Alert Bay and Kitimat, also recorded the 1952 Kamchatka tsunami, which generated a maximum wave height of 77 cm at Tofino. The 1957 Andreanof Islands tsunami was recorded at six primary stations and the 1960 Chile tsunami by 17 primary and temporary tide gauges. For both of these events, the maximum tsunami wave heights also occurred at Tofino: 48 cm (1957) and 132 cm (1960). The 1964 Alaska tsunami remains the strongest tsunami yet instrumentally recorded on the coast of British Columbia. Our examination of 16 records from this event shows that maximum wave heights at eight stations were higher than 1 m, including Port Alberni (770 cm), Ocean Falls (376 cm), Tofino (237 cm) and Alert Bay (222 cm). We also find that the maximum wave at all stations for this event was among the first three waves. Subsequent wave heights rapidly attenuated following this group of waves. Frequency-time (〈em〉f–t〈/em〉) analyses of the tsunami waveforms reveal that, for each station, the dominant frequencies of the waves and their evolution with time were very similar for different tsunamis, but differed considerably among sites for a particular tsunami, indicating the strong influence of local/regional topography on the incoming waves. From the latter point of view, the 1964 tsunami was exceptional. The epicentre of the 1964 Alaska earthquake was located much closer to the BC coast than for the other events and, therefore, the influence of the source was much stronger. The “ringing” of this tsunami was substantially shorter (〈 1.5 days), the energy decay much faster, and the 〈em〉f–t〈/em〉 diagrams at all sites more similar than for the other major events. During the 1964 event, energy associated with the dominant period of 2 h rapidly decayed. All of the tsunamis examined penetrated deep inside the narrow channels, fjords and inlets, typical of the BC coast. Waves also propagated far into some of the rivers. The 1952 Kamchatka tsunami was recorded at Kitimat, located at the head of Kitimat Arm about 80 km from Hecate Strait, while the 1957 Andreanof Islands tsunami was measured at Bella Coola, located at the remotest part of Burke Channel, a distance of ~110 km from the open ocean (Queen Charlotte Sound). The 1960 Chile tsunami was recorded at five stations located in the complex network of inlets and channels that make up the Seymour–Belize Inlet system on the central mainland coast of British Columbia, while the 1964 Alaska tsunami was observed at many stations in the Fraser River, including Pitt Lake that is connected to the Strait of Georgia through a 64-km route upstream in the Fraser and Pitt rivers. Our results further show that occasionally the fjords and inlets of the BC coast not only do not hinder the incoming waves but can strongly enhance them through resonant amplification. This was the case for the 1964 tsunami waves in Alberni Inlet, where the resonant response to the incoming waves resulted in severe damage to Port Alberni at the head of the inlet. The results of our analyses make it possible to isolate the tsunami signal and evaluate the principal parameters of tsunami waves. This, in turn, is of considerable value for three major problems: (1) Cataloguing of tsunami events; (2) estimation of the potential tsunami risk to the BC coast; and (3) verification and calibration of numerical tsunami models.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉A systematic inspection of the magnetic field and electron density, recorded by Swarm three-satellite constellation over the seismic region hit by the 2016–2017 Amatrice-Norcia (Central Italy) seismic sequence, has allowed us to identify some possible precursory anomalies, when disturbed periods of the geomagnetic conditions are properly taken into account and/or avoided. This paper aims at studying and interpreting the electromagnetic phenomena occurred before and during the 2016–2017 Amatrice-Norcia (Central Italy) seismic sequence, in order to look for any possible evidence of precursory anomalies. Results show magnetic field and electron density anomalies of four tracks that precede the major earthquakes of the seismic sequence. After an inspection of the geomagnetic conditions, a Swarm Charlie track, acquired on 20/08/2016 that precedes by 3.2 days the beginning of the whole seismic sequence, remains unexplainable with the normal geomagnetic disturbance phenomena of the Earth’s magnetic field. Furthermore, we carry out a blind study of possible relationship between abnormal magnetic field signals detected by Swarm satellites during geomagnetic quiet conditions and major seismic events from about 4 months before the start of the seismic sequence until about the first 8 months from the seismic sequence (i.e. a total of one year of analysed data). We find a very interesting increase of such anomalies starting about 40 days before the beginning of the seismic sequence. It coincides and follows surface and atmospheric alterations, resulting in a temporal sequence of anomalies from Earth’s surface up to ionosphere, supporting the possibility of lithosphere–atmosphere–ionosphere coupling models.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We present a new sampling scheme for seismic network observations and seismic exploration data acquisition based on compressive sensing theory. According to this theory, seismic data can be recovered with a compressive sampling scheme, using fewer samples than in traditional methods, provided that two prerequisites are met. The first prerequisite is sparse representation of the data in a transform domain. We use a one-dimensional wavelet transform to sparsely express the waveform data of the seismic network. For seismic exploration data, we use a curvelet transform as the sparse transform. The second prerequisite is incoherence between the sampling method and sparse transform. To enhance the incoherence, we propose a random sampling scheme for network and exploration observations, as random sampling is incoherent to most data transforms. In particular, we propose temporal random sampling for seismic network data observation and a full random sampling scheme in time and space for seismic exploration data. Compared with random sampling in spatial dimensions only, full random sampling further enhances incoherence because it adds the temporal dimension for randomization. Finally, seismic data are recovered from the compressive sampling data by calculating a sparsity-promoting algorithm in the sparse transform domain. We perform a real data test and synthetic data tests to illustrate that the proposed method can be used stably to achieve compressive sampling and successful recovery of high-resolution seismic waveform data. The results show that good sparse representation of the data and high incoherence between the sampling scheme and the data are important for successful recovery.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In this work, we search for physical and chemical climatological anomalies preceding major volcanic explosive eruptions (mostly VEI—Volcanic Explosivity Index 4+) occurred from 2002 to 2017, by applying two specific algorithms, i.e. CAPRI and MEANS. The former algorithm has been already used for a multi-climatological analysis of the Amatrice-Norcia 2016–2017 earthquake preparatory phase (Piscini et al., In: Pure Appl Geophys, 174:3673–3688, 〈span〉2017〈/span〉). Here we analyse some climatological parameters for a three-month period before each volcanic explosive eruption then we compare the behavior with the typical one of the past. The analysis is applied to an area with dimensions comparable to the volcano crater, because it is the increase of the magmatic camera activity that, in turn, can cause a temperature increase whose evidence could be detected at the surface (Slezin, In: J Volcanol Geotherm Res, 122(1–2), 7–50, 〈span〉2003〈/span〉), while the use of a larger area would provide a greater probability of occurrence of other events (e.g., other volcano eruption, meteorological storms, etcetera). Therefore, a smaller area of study reduces the risk to get “false alarms”. In particular, we considered thermal skin temperature, (skt) and total water vapour content (tcwv) from ECMWF European centre and aerosol optical thickness (AOT), sulphur dioxide (SO〈sub〉2〈/sub〉) and atmospheric dimethylsulphide (DMS) are obtained from NASA MERRA-2 Global Modeling and Assimilation data archive. The latter compound was added in the analysis to check the validity of the method, since we did not expect significant anomalies from this parameter. The models above described are used for their temporal-spatial completeness, allowing performing time series analyses and for a real time monitoring on a global scale. By simultaneous analysis, we found for almost all volcanic eruptions some anomalies in about all analyzed parameters that precede by 75 days to 20 days the explosion. These anomalies are not always simultaneous, but we find an interesting synchronicity that probably reveals a correlation among the different datasets. In addition, the Agung volcano, which has recently started an eruptive activity (25 November 2017) without reaching a VEI4+ explosion, has also been investigated. The data related to this volcano present a small number of anomalies, much lower than all attributed to the other analyzed explosive volcanoes and this is in high agreement with the low-explosive nature of the Agung volcano eruption. We find that the occurrence of thermal anomalies typically preceding stratovolcano/caldera eruptions seems to take place some days after SO〈sub〉2〈/sub〉 emissions. The climatological anomalies that precede eruptions at high latitudes usually surround the volcano in a wider area outside the volcanic edifice. We verify that the number of positive anomalies is systematically greater in the year that precedes the investigated eruption with respect to a quiet year of comparison with accuracy from 91 to 100%, suggesting that the applied methods detected climatological anomalies likely related to imminent volcanic eruptions.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The reliable forecast of imminent future earthquakes is still questionable due to uncertainties regarding the complex phenomena of earthquake occurrence and the hierarchical nature of the lithosphere. However, numerous retrospective studies suggest the implications of earthquake-accompanying processes within the context of earthquake forecasting. In this connection, an attempt is made here to verify the enhancement in thermal IR emissions associated with the extraordinary major (〈em〉M〈/em〉 7.7) and shallow (depth ≈ 15 km) Awaran earthquake (Sep 24, 2013). The satellite thermal imagery record is analyzed to identify the possible effect of pre- and post-seismic changes around the epicentral region (latitude 25–29°N; longitude 63–67°E) for a suitable selected time window (July 27, 2013 to Nov 16, 2013). The pre-earthquake satellite imagery records reveal a very clear and distinct thermal anomaly developed within the earthquake preparation zone almost 6–10 days earlier, while the analysis of post-earthquake imagery record shows a decreasing trend of thermal anomaly as a function of time. The daily land surface temperature (LST) shows an anomalous rise of 7–9 °C on Sep 18, 2013, almost 6 days prior to the event occurrence, which is further authenticated by the statistical criterion 〈span〉 〈span〉\((\bar{x} \pm 2\sigma )\)〈/span〉 〈/span〉 with a confidence interval of 95%. Furthermore, the comparative and percentile analysis of daily and 5-year-averaged LST also exhibits abnormal increase associated with this particular event. In addition to all above, the present study is also consistent with the earlier findings and suggests a multi-precursory strategy for earthquake forecasting research.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We performed a study of ground motion modeling based on multiple linear regression and random vibration theory using the earthquake sequence of September 8, 2017 (Mw = 8.2). Our results show that there is high attenuation in the region of Oaxaca–Chiapas and central Mexico; however, the peak amplitude excitations of normal fault earthquakes are higher than those of thrust fault earthquakes. The earthquake sequence involved a large number of events, but not all the seismic events were aftershocks because many earthquakes had different rupture styles. The thrust events follow a simple scaling relation with a constant stress parameter, but the normal fault events are difficult to represent with a constant self-similar model. Our best result consists of a 〈span〉 〈span〉\(Q_{0} = 240 \pm 032\)〈/span〉 〈/span〉 with a frequency-dependent factor of 〈span〉 〈span〉\(0.63 \pm 0.05\)〈/span〉 〈/span〉. The excitation term is well determined with a stress parameter of 80 bars for the thrust faults, but for the normal faults, the stress parameter is at least 180 bars with a non-self-similar model. Our results show that it is necessary to include new ground motion prediction equations in seismic hazard analysis for “meganormal” faults, which have not previously been considered in subduction zones.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉On September 28th, 2018, a powerful earthquake (M〈sub〉w〈/sub〉 7.5) struck the Island of Sulawesi in Indonesia. The earthquake was followed by a destructive and deadly tsunami that hit the Bay of Palu. A UNESCO international tsunami survey team responded to the disaster and surveyed 125 km of coastline along the Palu Bay up to the earthquake epicentre region. The team performed 78 tsunami runup and inundation height measurements throughout the surveyed coastline. Measured values reached 9.1 m for the runup height and 8.7 m for the inundation height, both at Benteng village. The survey team also identified ten large coastal sectors that collapsed into the sea of Palu Bay after the earthquake. The distribution of the measured tsunami data within Palu Bay exhibits a clear localised impact suggesting the contribution of secondary non-seismic local sources to the generation of the tsunami. Findings of the field reconnaissance are discussed to provide an insight into the remaining debated source of the Palu tsunami.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We evaluate the impact of natural and anthropogenic loadings on Indian maximum (〈em〉T〈/em〉〈sub〉max〈/sub〉) and minimum (〈em〉T〈/em〉〈sub〉min〈/sub〉) temperature variabilities during 1901–2015 using multiple spectral and statistical analyses. We compare the significant eigenmodes of temperature with TSI, Ocean and Atmospheric Processes (OAP) such as ENSO, PDO, NAO, AMO and CO〈sub〉2〈/sub〉 data to understand their influence on temperature. The present analysis is based on new eigen-weighted correlation coefficient (EWCC) and regression analysis to assess the sensitivity of temperature to TSI, OAP and CO〈sub〉2〈/sub〉. The first eigenmodes (EM) of 〈em〉T〈/em〉〈sub〉max〈/sub〉 and 〈em〉T〈/em〉〈sub〉min〈/sub〉 representing the long-term trend correlate well with the first EM of TSI (EWCC: 0.90 and 0.78) and CO〈sub〉2〈/sub〉 (EWCC: 0.95 and 0.72), respectively. The CO〈sub〉2〈/sub〉 residing throughout the day and night in the atmosphere may produce a similar linearly increasing trend in 〈em〉T〈/em〉〈sub〉max〈/sub〉 and 〈em〉T〈/em〉〈sub〉min〈/sub〉. However, the trend test revealed non-stationarity in the trends of 〈em〉T〈/em〉〈sub〉max〈/sub〉 and 〈em〉T〈/em〉〈sub〉min〈/sub〉. In addition, the regression analysis revealed high sensitivity of the 〈em〉T〈/em〉〈sub〉max〈/sub〉 and 〈em〉T〈/em〉〈sub〉min〈/sub〉 trend to TSI compared with CO〈sub〉2〈/sub〉. Our study suggests that there is an intermittent change in the running mean of TSI between 1901 and 2015 resulting in observed changes in 〈em〉T〈/em〉〈sub〉max〈/sub〉. In addition, spectral analysis of the 〈em〉T〈/em〉〈sub〉max〈/sub〉 and 〈em〉T〈/em〉〈sub〉min〈/sub〉 records revealed statistical significant  periodicities of ~ 2–7 years and 11 ± 2 years in 〈em〉T〈/em〉〈sub〉max〈/sub〉 and ~ 2–7 years and 50 ± 4 years in 〈em〉T〈/em〉〈sub〉min〈/sub〉, which may be associated with OAP and TSI, respectively. Based on the present analyses, we conclude that there are combined responses of (1) intrinsic variation in TSI and CO〈sub〉2〈/sub〉, which may be interpreted as the major loading factors on the trend of 〈em〉T〈/em〉〈sub〉max〈/sub〉 and 〈em〉T〈/em〉〈sub〉min〈/sub〉, respectively; (2) periodic variabilities in different frequency bands may be associated with both solar and ocean atmospheric processes depending upon time scales.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉On the basis of the continuous and dense GPS observations covering the northern segment of the Xiaojiang fault zone (n-XJFZ) from March 2012 to March 2016, we present the velocity field, spatiotemporal deformation, slip rate and locking depth of the n-XJFZ. The results provide strong support for achieving a better understanding of the deformation behavior of this fault. The heterogeneity of the GPS velocity field and relatively nonuniform distribution of seismicity suggest that the observational area is fragmented. Shear strain has been accumulating with an almost constant azimuth, which is consistent with the trends of the mapped major faults. The 2014 〈em〉M〈/em〉s 6.5 Ludian earthquake produced a sudden change in the dilatational strain, which was almost constant prior to the event, and an increase in the shear strain rate. The near-field deformation of the n-XJFZ estimated with the near-field data was larger than expected, revealing that the n-XJFZ is becoming more locked. These results imply that the seismic risk in the study area is currently rising and that, similar to the 2014 〈em〉M〈/em〉s 6.5 Ludian earthquake, future earthquakes will possibly occur away from mapped faults.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The Spanish Geophysical Data National Archive (Toledo Geophysical Observatory) is a centre created by 〈em〉Instituto Geográfico Nacional〈/em〉 to collect all the geophysical documentation produced in all of the observatories IGN has had in operation throughout its history. All this information is transferred to the Geophysical Data National Archive where it is reviewed, classified and catalogued in a database, to be eventually filed in the records repository of the Archive, with the appropriate conditions for their future preservation. Its contents are digitized as backup and to meet the data requests received in this Archive. For the study of earthquakes throughout the twentieth century, this Archive has a large volume of information. The documents most consulted by researchers are the seismic records from the IGN Geophysical Observatories, but also the Archive houses an important collection of complementary information.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In this work, observations of ocean wave height from satellite altimeters are assimilated into the coastal wave model simulating waves nearshore (SWAN) operating in the Indian coastal waters. The study has two distinctive features. The most important is the use of certain concepts of the modern particle filter technique, which does not represent the model probability density function (PDF) by a Gaussian. The other feature is the joint assimilation of data from three altimeters. The method starts by generating an initial ensemble by the bootstrap technique in which the significant wave height (SWH) field of a control run is perturbed by randomly adding bias to produce a member of the ensemble. At the first assimilation time, a weight-based resampling of the individual members, known as particles, is performed. Stronger particles are retained, while the weaker ones are discarded. In order to keep the ensemble size constant, the algorithm replicates a few strong members. After this resampling, a single model run is employed in the forecast step using a kind of averaging. At the next assimilation time, a synthetic ensemble is again formed by the same bootstrapping, and observations are assimilated. The forecast–assimilation cycle is repeated until the observations are exhausted. Assimilation experiments were conducted for 6 months from February through July in 2016. The power of the technique is evaluated by validating results with altimeter data as well as independent data sets from moored buoys. The results are found to be extremely encouraging for the use of this method in carrying out coastal wave forecasting.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Seismic intensity for the February 28, 1969 (Mw = 7.8) earthquake have been re-evaluated using original documents in local archives, such as, contemporary newspapers, council minutes, monographic studies, among other sources for Spain, Portugal and Morocco and answers to macroseismic questionnaires for Morocco. This information is used to plot a new intensity map for the whole region affected by the earthquake: Portugal, Spain and Morocco. The intensity values vary from VIII to IX in the E-W coast of Algarve, southern Portugal, to II–III. Furthermore, we have relocated the hypocentres for main shock and 24 aftershocks using a new 3D crustal velocity model for the Gulf of Cadiz region and a non-linear probabilistic location methodology, most of them previously lacking a depth estimate. The new locations show an E-W distribution of epicenters, with focus located in the uppermost mantle, most of them with depths between 30 and 50 km. No earthquakes have been located at depths shallower than 30 km. A comparison between peak ground accelerations (PGAs) estimated from the observed intensities for the 1969 and the Lisbon 1755 earthquakes, and synthetic PGA values, generated assuming two different scenarios (using the 1969 and 2009 earthquakes) for the 1755 Lisbon event, shows that the observed damage produced by the 1755 earthquake may be better explained assuming a reverse dip-slip mechanism oriented in NE-SW direction, similar to that of the 2009 earthquake, rather than assuming focal mechanism similar to that of the 1969 earthquake.〈/p〉

Description: 〈p〉Owing to an unfortunate oversight, the wrong figure 2 has been published.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We present an objective technique for assessing the fundamental resonance frequency (〈span〉 〈span〉\({\text{f}}_{0}\)〈/span〉 〈/span〉) of a given site through horizontal-to-vertical (H/V) spectral ratio. H/V spectral ratios have been determined from 5%-damped spectral acceleration derived from strong-motion time histories recorded at accelerograph stations. The technique has been applied to an updated comprehensive strong ground-motion database from Iran. In this study, the resultant 〈span〉 〈span〉\({\text{f}}_{0}\)〈/span〉 〈/span〉 values have been also evaluated through visual inspection of average H/V response spectral ratios for each station as well as detailed inspection of vertical and horizontal spectral components of all events recorded at each station. The technique has been applied to 389 stations of the Iran Strong Motion Network (ISMN), from which 〈span〉 〈span〉\({\text{f}}_{0}\)〈/span〉 〈/span〉 values have been determined for 266 stations. The determined 〈span〉 〈span〉\({\text{f}}_{0}\)〈/span〉 〈/span〉 values have been used to estimate time-averaged shear-wave velocity in the upper 30 m (〈span〉 〈span〉\({\text{V}}_{{{\text{S}}30}}\)〈/span〉 〈/span〉), taking into account the correlation between H/V parameters and measured 〈span〉 〈span〉\({\text{V}}_{{{\text{S}}30}}\)〈/span〉 〈/span〉 values at recording stations. Results and corresponding model uncertainties have been compared with other related studies conducted for Japan, Central and Eastern North America as well as a global model. In comparison with other datasets, the Iranian 〈span〉 〈span〉\({\text{V}}_{{{\text{S}}30}}\)〈/span〉 〈/span〉 model shows the highest 〈span〉 〈span〉\({\text{V}}_{{{\text{S}}30}}\)〈/span〉 〈/span〉 values among all models. We use the region-specific equation developed in this study to estimate 〈span〉 〈span〉\({\text{V}}_{{{\text{S}}30}}\)〈/span〉 〈/span〉 values for 63 stations of ISMN where no other site characterization was available.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉This study reports the estimation of source parameters in and around Izmir, western Anatolia (Turkey), using data recorded by 18 strong motion stations belonging to the local accelerometer array (IzmirNET). The displacement spectra of SH waves are calculated for 55 earthquakes with a moment magnitude range (〈em〉M〈/em〉〈sub〉w〈/sub〉) of 3.4 to 5.7 recorded by at least ten stations. The corner frequency (〈em〉f〈/em〉〈sub〉0〈/sub〉), spectral level and 〈em〉f〈/em〉〈sub〉max〈/sub〉 are acquired from the displacement spectra in order to analyse the source characteristics of the events using Brune’s source model. Seismic moment (〈em〉M〈/em〉〈sub〉0〈/sub〉) values are computed between 12.74 and 17.93 Nm, spectral level (〈em〉Ω〈/em〉〈sub〉0〈/sub〉) values are detected between 3.17 and 6.44 nm s, source radius (〈em〉r〈/em〉) values are calculated from 0.45 to 2.28 km, and seismic energy values are estimated between 2.07 × 10〈sup〉13〈/sup〉 and 6.45 × 10〈sup〉20〈/sup〉 erg. Computed stress drop (Δ〈em〉σ〈/em〉) values vary from 0.72 to 346.9 bar, and this result is significantly lower than the values of 0.017 and 647.6 bar reported for the Marmara region, northwestern Anatolia (Turkey), and slightly lower than the source sizes of the events of between 0.0862 and 5.1042 km. However, similar results were found for seismic moments (Koseoglu et al., in J Seismol 18:651–669, 〈span〉https://doi.org/10.1007/s10950-014-9435-2〈/span〉, 〈span〉2014〈/span〉). From the results of the present study, it is concluded that scattering in seismic moment, stress drop and hypocentral distance during large earthquakes is observed by an increase in 〈em〉f〈/em〉〈sub〉0〈/sub〉 and 〈em〉f〈/em〉〈sub〉max〈/sub〉 , which is related to the complex tectonism of the study area.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The southeast margin of Tibet is the region in clockwise rotation around the Eastern Himalayan Syntaxis due to the India–Eurasia collision and the resistance of the stable Sichuan Basin and South China block. However, the dynamic processes involved in the evolution and deformation of the region remain poorly understood due to a lack of reliable geophysical observations. We collected abundant seismic data recorded by 108 permanent broadband stations deployed in the SE margin of Tibet since 2000, and obtained 4536 pairs of P-wave receiver functions (PRFs) with high signal-to-noise ratio. In this study, we have implemented a novel two-step data inversion procedure that can reduce the dependence of the inversion results on the initial model. We first use low-frequency PRFs obtained by iterative deconvolution in the time domain, and then an initial model consisting of a series of 2-km-thick isotropic layers to fit velocity models, and thus determine an overall statistical solution by means of the bootstrap resampling technique. This statistical solution is then regarded as a new initial model to adjust high-frequency PRFs. Hence, the same resampling process is executed again to estimate the optimal S-wave velocity structure below each station. The results provide an accurate 3D image of the crust and uppermost mantle in the SE margin of Tibet. We infer a wide intra-crustal low-velocity zone that varies laterally and in depth, which is thinner or even absent in the most southern part of Yunnan. Our hypothesis is that this low-velocity zone is the result of the accumulation of lower crustal flow coming from central Tibet. Furthermore, we show that this lower crustal flow extends largely through the Sichuan–Yunnan diamond-shaped block, and that there are significant variations in both crustal velocity structure and deformation mechanism across the great strike-slip faults of the Jinshajiang–Red River and Xiaojiang fault systems.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The catastrophic Sanyanyu and Luojiayu debris flows, which were induced by heavy rain, struck Zhouqu County in Gannan Prefecture, Gansu Province, at approximately midnight, 7 August 2010 (Beijing time, UTC + 8), causing 1765 fatalities and huge economic loss. The ZHQ seismic station is located approximately 170 m west of the outlet of the Sanyanyu gully, and its power system was destroyed by the Sanyanyu debris flow when its leading edge reached the vicinity of the seismic station. In this paper, seismic signals recorded approximately 10 min before its termination are collected and analyzed to study the Sanyanyu debris flow. A double-exponential model is first proposed to quantitatively characterize seismic energy distributions in the frequency domain, which reveals that the peak frequency of seismic signals is around 5 Hz. Influenced by the Doppler effect, the peak frequency of the N–S component is the highest, and the U–D component is the lowest. Time–frequency analysis is applied to the seismic signals. From the spectrogram, it is easily observed that the formation time of the Sanyanyu debris flow is around 23:33:10. The entire debris flow is divided into three phases with distinct frequency characteristics, using 23:36:20 and 23:37:35 as crucial times. The frequency energy distributions in the first two phases are relatively stable, and are constrained in 0–8.8 Hz and 0–17.8 Hz, respectively. For the third phase, the upper boundary of frequency energy increases in a nearly linear manner, reaching approximately 35 Hz at the end. We calculate synthetic seismograms of the Sanyanyu debris flow. Generally, synthetic seismograms have morphological features and characteristics in key stages similar to those of the actual seismic records, and their maximum values are of the same magnitude. Our results suggest that the seismic source of a debris flow can be represented by a single-force model, and reveal that real-time monitoring and rapid identification of potential debris flows using broadband seismic network records is possible, which can provide approximately 15 min of pre-event warning for local residents and hopefully save many lives.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The absolute permeability of rock depends on several factors, including porosity, 〈span〉 〈span〉\(\phi \)〈/span〉 〈/span〉, the geometry of the pore network (tortuosity), and the grain geometry, dimension and composition. The mineralogical composition plays an important role, mostly with respect to clay, which involves several components including illite, smectite, kaolinite and chlorite. The presence of quartz and feldspar increases permeability, while clay minerals and calcite tend to have the opposite effect. Essentially, permeability decreases with a smaller grain radius, increasing tortuosity of the pore space and decreasing porosity. As the specific surface area of the pores increases, permeability decreases. Here, we compare four expressions for permeability based on clay content, grain dimension, tortuosity and mineral composition. All the expressions somehow contain the Kozeny–Carman (KC) factor 〈span〉 〈span〉\(\phi ^{3} /(1 - \phi )^{2}\)〈/span〉 〈/span〉, which is obtained on physical grounds, and relies on fitting parameters related to the geometric characteristics of the rock and its composition. The Herron model is based on geochemical mineralogy composition. Despite the highly idealized parameters on which these models are based, the results support the predictive power of the Kozeny–Carman equation, provided that proper calibration is performed.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉This article characterizes the regions of earthquake slip that are responsible for strong motion generation (SMG), using extreme value theory (EVT). A three-step iterative procedure involving Zipf plot, mean excess function plot and moment ratio plot is used to define the threshold value for a slip model. This threshold slip demarcates the region of SMG in the slip model. The iterative procedure ensures that slip values above the threshold slip follow generalized Pareto distribution (GPD). The regions where slip is greater than the corresponding threshold slip are defined as regions of SMG. A total of 159 slip samples filtered from the SRCMOD catalogue are analyzed in this paper. In order to identify the region of SMG, the first step is to obtain effective slip dimensions. A novel method based on strong motion duration (SMD) is proposed to obtain the effective dimensions of slip model. In the next step, the iterative procedure is employed to obtain threshold slip and the regions of SMG for all the slip samples. The corresponding area of SMG is estimated from the number of sub-faults in the region of SMG and the sub-fault dimensions. Regression analysis is carried out to establish source scaling relationships for the rupture parameters with respect to seismic moment. The considered rupture parameters are effective length, effective width, effective area, effective mean slip, threshold slip and area of SMG of the slip model. On a logarithmic scale, these rupture parameters are observed to follow a linearly increasing trend with the seismic moment. The proposed equations can be used to estimate the rupture parameters for future earthquake events.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Shallow aseismic creep is a key deformation component along plate boundaries that contributes to the energy budget during the seismic cycle. Several major active continental faults show spatial alternation of creeping and locked sections. The present study focuses on the evaluation of the aseismic part of the total displacement along the North Anatolian Fault in Turkey. Detailed microstructural analyses of finite strain were performed using various methods, based on change of length or angle, on six representative samples collected over 32 outcrops along locked and creeping sections of the fault. Chemical analyses were used to map mineral composition of fault rocks and to calculate relative volume changes associated with creep. The relationship between finite strain and volume change allowed quantifying the evolution of the penetrative pressure solution cleavage mechanism of creep. In volcanic and analogous creeping rocks, finite strain measurements revealed two spatial scales of strain that correspond to the alternation of two types of shear zones, with cleavages either oblique or sub-parallel to the fault displacement. Using geodetic and geologic data, cumulative aseismic displacement was calculated in the range 9–49% of the total 80-km displacement in the creping sections and was negligible in locked sections. The large uncertainty in the kilometer-width creeping sections was related to the difficulty of quantifying the high strain values associated with high shear displacement and for which measurement uncertainties are large. A promising way to improve such quantification would be to develop reliable statistical analysis of cleavage orientation in the field.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Ambient noise tomography (ANT) has been used successfully to image shallow earth structure. Here we perform ANT on a local dense seismic array around the Tanlu fault zone (TFZ) to the southeast of Hefei City, Anhui Province in eastern China. The array consists of 53 stations with average spacing close to 5 km. Cross-correlations of vertical-component ambient noise data of different station pairs are computed in 1-h segments and stacked over 1 month from 17 March to 26 April 2017. Clear fundamental-mode Rayleigh waves are observed between 0.2 and 5 s period. We then use the direct surface-wave tomographic method with period-dependent ray tracing to invert group and phase dispersion travel-time data simultaneously for three-dimensional (3D) shear-wave velocity (〈em〉V〈/em〉〈sub〉s〈/sub〉) structure. The 〈em〉V〈/em〉〈sub〉s〈/sub〉 model shows clear correlation with the known geologic features. The TFZ is associated with a high-velocity anomaly zone in the shallow crust, corresponding to metamorphic rocks due to magma intrusion. Low-velocity anomaly zones are mainly located to the west of the TFZ, caused by thick sedimentary layers in the Hefei Basin. Our study shows that, with ambient noise data recorded on a dense array and an advanced surface-wave inversion method, we can image detailed structure around the fault zone.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The long rupture length and complex fault geometries of the 2008 〈em〉M〈/em〉〈sub〉w〈/sub〉 7.9 Wenchuan earthquake offer a great opportunity to investigate the relationship between coseismic radiation and fault complexities. In this study, we first improved the compressive-sensing back-projection method (CS-BP) with window time adjustment and parallel computation to enhance its spatial–temporal resolution and computational efficiency. Then we applied the CS-BP to invert for the coseismic radiation of the Wenchuan earthquake in multiple frequency bands. Our results show that the coseismic radiation of the Wenchuan earthquake is frequency-dependent and strongly associated with the fault geometries: low-frequency radiation sources are concentrated on smooth fault segments with large coseismic slip, while higher-frequency sources are mainly related to fault complexities (e.g., Xiaoyudong fault, Gaochuan fault-bend, Leigu fault-bend, and Nanba fault step-over). An acceleration of rupture speed from ~ 1.5 to ~ 3.0 km/s is also observed the near Xiaoyudong fault, where strong high-frequency energies were radiated. Finally, we discuss the role of rupture speed in mediating the relationship between coseismic radiation and fault complexities. On one hand, sudden changes of rupture speeds contribute to strong high-frequency radiation. On the other hand, fault complexities can also strongly affect the rupture speed: a sudden break of a large asperity is able to propel the acceleration, while rupture front may decelerate when it jumps across geometric barriers.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Site-specific seismic hazard studies involving detailed account of the site response require the prior estimate of the hazard at the local reference bedrock level. As the real characteristics of such local bedrock often correspond to “hard-rock” with S-wave velocity exceeding 1.5 km/s, “standard rock” PSHA estimates should be adjusted in order to replace the effects of “standard-rock” characteristics by those corresponding to the local bedrock. The current practice involves the computation of scaling factors determined on the basis of V〈sub〉S〈/sub〉 (S-wave velocity) and “κ〈sub〉0〈/sub〉” (site specific, high-frequency attenuation parameter) values, and generally predicts larger high-frequency motion on hard rock compared to standard rock. However, it also proves to be affected by large uncertainties (Biro and Renault, Proceedings of the 15th world conference on earthquake engineering, 24–28, 〈span〉2012〈/span〉; Al Atik et al., Bull Seism Soc Am 104(1):336–346 〈span〉2014〈/span〉), mainly attributed to (i) the measurement of host and target parameters, and (ii) the forward and inverse conversions from the response spectrum domain to the Fourier domain to apply the V〈sub〉S〈/sub〉 and κ〈sub〉0〈/sub〉 adjustments. Moreover, recent studies (Ktenidou and Abrahamson, Seismol Res Lett 87(6):1465–1478, 〈span〉2016〈/span〉) question the appropriateness of current V〈sub〉S 〈/sub〉− κ〈sub〉0〈/sub〉 scaling factors, so that the significant amplification of high frequency content for hard-rock with respect to standard-rock seems overestimated. This paper discusses the key aspects of a few, recently proposed, alternatives to the standard approach. The calibration of GMPEs directly in the Fourier domain rather than in the response spectrum domain is one possibility (Bora et al., Bull Seism Soc Am 105(4):2192–2218, 〈span〉2015〈/span〉, Bull Earthq Eng 15(11):4531–4561, 〈span〉2017〈/span〉). Another possibility is the derivation of GMPEs which be valid also for hard-rock conditions (e.g. Laurendeau et al., Bull Earthq Eng 16(6):2253–2284, 〈span〉2018〈/span〉). In this latter case the host site response is first removed using theoretical site response analyses (and site velocity profile), or generalized inversions techniques. A third possibility is to use existing hard rock surface recordings to derive purely empirical scaling models from standard rock to hard rock (Ktenidou et al., PEER Report, Pacific Earthquake Engineering Research Center, Berkeley, 〈span〉2016〈/span〉). Finally, when a sufficient amount of records are available at a given site, generic GMPEs can be scaled to the site-specific ground motion using empirical site residual (δ〈sub〉S2Ss〈/sub〉) (Kotha et al., Earthq Spectra 33(4):1433–1453, 〈span〉2017〈/span〉; Ktenidou et al.,  Bulletin of Earthquake Engineering 16(6):2311–2336, 〈span〉2018〈/span〉). Such alternative approaches present the advantage of a significant simplification with respect to the current practice (with thus a reduced number of uncertainty sources); their generalization calls however for high-quality recordings (including high-quality site metadata) for both host regions and target sites, especially for small to moderate magnitude events. Our answer to the question in the title is thus “No, alternative approaches exist and are promising; though, their routine implementation requires additional work regarding systematic site characterization (for the host regions) and high-quality site characterization/instrumentation (for the target site), and so do also the needed improvements of the existing HTTA procedure”.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The main goal of the research presented was to design and construct a device, enables estimation of the diffusion time and diffusion length for radon in core samples collected from the geological layers of Upper Silesian Coal Basin (USCB). Another goal will be investigations of the advection of 〈sup〉222〈/sup〉Rn with other gases like carbon dioxide or methane, occurring in the Carboniferous strata in USCB. This knowledge will support the precision of the assessment of radon hazard in working environment. Moreover, it should give an answer to some questions, related to the radon migration issues—if the results of measurements of the transport of radon with other gases in the strata could be applied for the prediction of geodynamic phenomena in the mining areas, like tremors and outbursts. The study was focused on the flow measurements of the following gases: radon, carbon dioxide, nitrogen and their mixtures, as the use of methane was excluded due to potential hazard of explosion. In this article results of measurements of diffusive migration are presented: radon itself and simultaneous migration of radon, nitrogen and carbon dioxide. For this purpose a special device was designed and constructed. This device consists of the container for the sample of coal, mineral or rock and two reservoirs—the inlet and outlet one. The gas (e.g. air or carbon dioxide) with radon is introduced into inlet reservoir, while the content of marker gases and radon is monitored in the outlet reservoir. The preliminary experiments were also performed and are presented in this paper. In the literature, there are only rare results of such investigations, while our previous research in USCB region showed some correlation between sudden changes of radon level and geodynamic events. Therefore, the results of the investigations presented in this study are expected to contribute to the improvement of the models of these phenomena. The future work planned will be aimed at investigations of advective flow of radon with various carrier gases.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Seismic data are increasingly used to monitor subsurface velocity changes associated with tectonic and environmental processes that occur in different depth sections. To clarify the differences between effects associated with shallow and deep changes of properties, we conduct numerical experiments using simple layered models that include low velocities, low attenuation coefficients and stress-sensitivity of cracked rocks in the shallow crust. We find significant phase-velocity drops in the period range of 5–20 s when large structural changes occur in the top 1–3 km. The apparent velocity changes (δv/v) measured from the first part of the synthetic Rayleigh waves with a cross-correlation based technique show significant velocity drops in the period bands of 5–10 s and 10–20 s that are consistent with reported values of changes at seismogenic depth. The results highlight the importance of accounting for low velocities, attenuation coefficients and stress-sensitivity of parameters in the top 1–3 km in studies aiming to determine the source region of temporal changes. Analyses using different frequency ranges and calculations of apparent delay times over multiple period bands are essential for resolving the depth range of temporal changes of properties. For temporal changes occurring at seismogenic depths, the measured δv/v values at 5–10 s are significantly larger than those of 10–20 s, which are not observed for shallow changes.〈/p〉

Description: 〈p〉With the author(s)’ decision to opt for Open Choice the copyright of the article changed on.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The 1960 M9.5 Valdivia and 1964 M9.2 Alaska earthquakes caused a decimeters high secondary zone of uplift a few hundred kilometers landward of the trench. We analyze GPS data from the 2010 M8.8 Maule and 2011 M9.0 Tohoku-Oki earthquakes to reveal the persistent existence of a secondary zone of uplift due to great earthquakes at the megathrust interface. This uplift varies in magnitude and location, but consistently occurs at a few hundred kilometers landward from the trench and is likely mainly coseismic in nature. This secondary zone of uplift is systematically predicted by our 2D visco-elasto-plastic seismo-thermo-mechanical numerical simulations, which model both geodynamic and seismic cycle timescales. Through testing hypotheses in both simple and realistic setups, we propose that a superposition of two physical mechanisms could be responsible for this phenomenon. First, a wavelength is introduced through elastic buckling of a visco-elastically layered fore-arc that is horizontally compressed in the interseismic period. The consequent secondary zone of interseismic subsidence is elastically rebound during the earthquake into a secondary zone of relative uplift. Second, absolute and broader uplift is ensured through a mass conservation-driven return flow following accelerated slab penetration due to the megathrust earthquake. The dip and width of the seismogenic zone and resulting (deep) coseismic slip seem to have the largest affect on location and amplitude of the secondary zone of uplift. These results imply that subduction and mantle flow do not occur at constant rates, but are rather modulated by earthquakes. This suggests a link between deep mantle and shallow surface displacements even at time scales of minutes.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Using a seismicity simulation program based on the Coulomb-Navier failure criterion and the stress transfer mechanism, we added extensions to make the model compatible with different input files and to increase computational efficiency. After testing with a two-vertical-parallel-fault model, we applied this model to the Taiyuan region. The frequency–magnitude data of the simulation results fit well with the observation catalogue, which at the same time tends to follow the characteristic earthquake theory instead of the Gutenberg-Richter law. In addition, a single fault region with a higher slip rate seems to have lower b-values, suggesting a higher risk of strong earthquakes. We have also performed data fitting between the simulation results and the Poisson process of corresponding parameters, along with testing for energy conservation.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The upper tropospheric thermal contrast over the northern Tibetan Plateau and the Tianshan Mountains during the peak summer monsoon is found to have experienced a significant change since the late 1990s, and the change is out of phase on the western and eastern sides of the northern Tibetan Plateau. Using the National Center for Environmental Prediction (NCEP)–DOE AMIP-II reanalysis daily data sets, we found that in the late 1990s, there was an increase/decrease in the tropospheric temperature (TT) at 100 hPa/300 hPa on the western side, whereas on the eastern side the TT changed in the opposite fashion. Associated with the TT change is an increase (decrease) in convection in the west (east). This is in agreement with the patterns of humidity fluxes and ascending/descending favorable winds, and has been further substantiated in a causal inference, which identifies a dominant causality from the TT variation over the western side of the northern Tibetan Plateau to the longwave and shortwave fluxes through the top of the atmosphere. The lack of causality from the eastern TT variation suggests a reduction in convection, hence cloudiness, over that region, which may account for the flash drought over China during the recent global warming hiatus.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The complexity of coseismic slip distributions influences the tsunami hazard posed by local and, to a certain extent, distant tsunami sources. Large slip concentrated in shallow patches was observed in recent tsunamigenic earthquakes, possibly due to dynamic amplification near the free surface, variable frictional conditions or other factors. We propose a method for incorporating enhanced shallow slip for subduction earthquakes while preventing systematic slip excess at shallow depths over one or more seismic cycles. The method uses the classic 〈em〉k〈/em〉〈sup〉−2〈/sup〉 stochastic slip distributions, augmented by shallow slip amplification. It is necessary for deep events with lower slip to occur more often than shallow ones with amplified slip to balance the long-term cumulative slip. We evaluate the impact of this approach on tsunami hazard in the central and eastern Mediterranean Sea adopting a realistic 3D geometry for three subduction zones, by using it to model ~ 150,000 earthquakes with 〈span〉 〈span〉\(M_{w}\)〈/span〉 〈/span〉 from 6.0 to 9.0. We combine earthquake rates, depth-dependent slip distributions, tsunami modeling, and epistemic uncertainty through an ensemble modeling technique. We found that the mean hazard curves obtained with our method show enhanced probabilities for larger inundation heights as compared to the curves derived from depth-independent slip distributions. Our approach is completely general and can be applied to any subduction zone in the world.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Materials in the Earth’s mantle behave as fluids over geological time scales, and this behavior greatly influences geoid anomalies at the Earth’s surface. However, many uncertainties remain regarding the origins of the Earth’s geoid anomalies. Additionally, uncertainties about the viscosity ratios between the upper and lower mantles still exist. Therefore, we model long-wavelength geoid anomalies from instantaneous mantle flow based on the density structure inferred by two recent S-wave tomographic models, SEMUCB_WM1 and S40RTS. In the simulation, we introduce specific viscosity values for certain tectonic regions in the lithosphere and a temperature-dependent viscosity for the mantle beneath the lithosphere. We compute the correlations between the modeled geoid anomalies and observations. Our results show that the geoid anomalies modeled based on the two tomographic models, SEMUCB_WM1 and S40RTS, achieve the best fits with the observations and present correlation coefficients of approximately 0.77 and 0.75 when the viscosity ratios between the lower and upper mantle are 80 and 70, respectively. These values fall toward the end of viscosity contrasts suggested from some previous geodynamic studies, which were 30–100.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉As Antarctica is almost entirely covered by thick ice shields impeding in situ measurements, information about upper crustal structures and sedimentary basins is still sparse and the analysis of the gravity anomalies offers new insights. Isostatic gravity anomalies are often used to investigate upper crust structures. However, compensating masses significantly reduce the gravity effect of unknown sedimentary and upper crustal structures. To separate these effects, we apply so-called decompensative corrections to the isostatic anomalies for the Antarctic continent, which reach values of up to ± 70 mGal. The obtained decompensative anomalies well correspond to the known sedimentary basins, such as in the areas of the Filchner-Ronne Ice Shelf and Lambert Graben, and also suggest the existence of other large sedimentary deposits both in West and East Antarctica, which are not or only sparsely mapped by existing seismic surveys, e.g. in coastal Dronning Maud Land and Enderby Land. A dipole-like structure exists at the Transantarctic Mountains and the Wilkes Subglacial Basin, suggesting the presence of isostatic disturbances linked to the dynamic uplift of the Transantarctic Mountains and thick sedimentary accumulations in the east. Extended positive anomalies in East Antarctica are likely related to the old and dense cratonic crust as well as to isostatic disturbances caused by the transition from local to regional compensation around the Lambert Graben.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉A combination of satellite-based and ground-based information is used to identify regions of intense convection that may act as a hazard to high-altitude aircraft. Motivated by concerns that Global Hawk pilotless aircraft, flying near 60,000 feet, might encounter significant convectively-induced turbulence during research overflights of tropical cyclones, strict rules were put in place to avoid such hazards. However, these rules put constraints on science missions focused on sampling convection with onboard sensors. To address these concerns, three hazard avoidance tools to aid in real-time mission decision support are used to more precisely identify areas of potential turbulence: Satellite-derived Cloud-top height and tropical overshooting tops, and ground-based global network lightning flashes. These tools are used to compare an ER-2 aircraft overflight of tropical cyclone Emily in 2005, which experienced severe turbulence, to Global Hawk overflights of tropical cyclones Karl and Matthew in 2010 that experienced no turbulence. It is found that the ER-2 overflew the lowest cloud tops and had the largest vertical separation from them compared to the Global Hawk flights. Therefore, cold cloud tops alone cannot predict turbulence. Unlike the overflights of Matthew and Karl, Emily exhibited multiple lightning flashes and a distinct overshooting top coincident with the observed turbulence. Therefore, these tools in tandem can better assist in identifying likely regions/periods of intense active convection. The primary outcome of this study is an altering of the Global Hawk overflight rules to be more flexible based on the analyzed conditions.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The choice of an effective interpretative methodology in terms of management costs, timing, reliability, safety and efficiency is a key issue for the identification of unexploded ordnance (UXO). Among geophysical methods, magnetometry plays an important role in detection and interpretation of UXO objects. We present a study aimed at the identification and characterization of buried UXO in Rohoznik, Slovakia, by a multiscale analysis on high-resolution magnetic data. The area is located close to a former army shooting range and is characterized by several buried UXO. When a UXO hits the ground but does not explode, the impact causes a re-organization of the magnetic domains within the armature (shock demagnetization). Due to shock demagnetization the object gets a magnetization oriented in the direction of the actual Earth magnetic field. Furthermore, the elongated shape of the UXO of Rohoznik causes their anomalies to be oriented along the longitudinal axis of the projectiles. Our multiscale analysis was performed through methods such as depth from extreme points (DEXP) and the multi-ridge method. The upward continuation employed by these two methods allowed reducing the influence of the high-frequency noise related to non-UXO buried iron objects. Also, the use of high-order derivatives in the multiscale approach decreased interference effects related to close-by sources and avoided any pre-filtering. Our approach was first validated on a test site located close to Rohoznik, where unexplored projectiles were buried with different orientations at a known depth. Then we focused on the real data of the former army shooting range. For all our analyses we employed a structural index value of 2.5, which was estimated through the scaling function analysis and the derivative euler deconvolution algorithm. Both the (DEXP) and multi-ridge depth-estimation methods proved to be effective and rapid with respect to more expensive and time-consuming methods such as inversion. Our analysis revealed average depths for the analysed UXOs matching rather well with what was found by subsequent excavations, with a maximum discrepancy of a few decimetres.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Analytical expressions for displacements and rotations in a homogeneous reduced micropolar half-space subjected to a finite buried source are derived using the method of potentials. Explicit solutions for displacements and rotations are derived for a uniformly distributed force acting over a circular region in the horizontal or vertical direction. The obtained solutions for displacements are validated against those available in literature for a classical elastic half-space. Finally, Green’s functions for displacements and rotations are derived for a unit impulse applied in the horizontal or vertical direction. In addition to analytical solutions, the paper also compares the dispersion phenomenon of compression and shear waves propagating in a reduced micropolar half-space with different material properties.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The East Kunlun Fault (EKF) is one of the largest and most active sinistral strike-slip faults in the Qinghai–Tibet Plateau. Since 1900, many earthquakes of magnitude 〉 7 have occurred in this region. The Maqin–Maqu Segment (MMS), a seismic gap underlying a densely populated zone, is particularly important. While the area has been extensively researched to assess seismic risk, refined asperity geodetic imaging is deficient. We combined multiple sets of GPS and leveling observations to obtain spatial–temporal distributions of locking along the EKF. We delineated the probable asperity ranges according to the fault plane locking and the distribution of small earthquakes. Long-term observations on GPS velocity (1999–2013) and leveling (1970–2013) indicate that the Dulan–Maduo segment (DMS) of the EKF has a 140-km-long strong coupling section, and both the MMS and the eastern Ruoergai segments have a 40-km-long locking range. The 2013–2015 GPS velocity observations show that from Maqu to Maqin, the locked DMS and MMS lengths increased to 200 km and 240 km, respectively, while the locked eastern Ruoergai segment decreased and migrated 60 km to the west. This change in locking over time implies that the post-seismic effects of surrounding earthquakes have had significant impacts on the EKF. The locking area derived from 2015 to 2017 GPS velocity shows a growing trend and indicates the connectedness between the two speculative asperities. Combining the distribution of historical earthquakes and the precision positioning of small earthquakes, we conclude that the geodetic imaging of the EKF indicates that the MMS and DMS are high-risk zones for destructive earthquakes.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The strike-slip earthquake on 28 September 2018 (Mw 7.5) along the Palu-Koro fault on Sulawesi Island has raised concerns about the potential impact of tsunamis generated by submarine landslides in Palu Bay, Indonesia. The horizontal displacement of the Palu-Koro fault generated landslide tsunamis that covered Palu Bay, creating wave-related hazards along the coastal area. Based on the unusual amount of information on this tsunami, this study investigated possible sources using the available preliminary data. The generation of comparatively small tsunamis by coseismic seafloor deformation is omitted, and only tsunamis generated by submarine/subaerial landslides are analyzed in this study. Two-layer modeling (soil and water) based on the shallow-water equation was used to simulate the tsunami propagation in the bay with severe, moderate, and minor impacts. The accuracy of the model was validated based on the waveform at the Pantoloan tidal gauge and trace data. The tsunami heights from a combination of small to large submarine landslides could reach up to 3.0–7.0 m along the Palu shores. This model focused on studying the effects of the tidal level on coastal inundation in Palu Bay, using the 2018 Palu tsunami event as a benchmark scenario, to demonstrate the capabilities of the model. One result shows that, regardless of the tidal level, the 2018 Palu tsunami, which occurred during high tide, will always result in flooding, with a maximum tsunami height of up to 7.0 m above mean sea level. The main results suggest two causes for this tsunami event: the tsunami source and the topography. First, the model requires one large source at the bay entrance to reproduce the arrival time (approximately 5 min) and the large wave observed at the Pantoloan gauge. To reproduce the later waves, small sources in the bay (S1–S6) and minor large sources (L2 and L3) are needed. Second, the datum correction for the terrain is changed to improve the accuracy of the water level. Additionally, the removal of buildings from the topography is important to achieve highly accurate flow depths and to obtain an inundation area close to the real situation. The impacts along the coastline of Palu Bay from peak waves can be used to identify tsunami hazards in the area in the future.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We analyzed a kinematic earthquake rupture generator that combines the randomized spatial field approach of Graves and Pitarka (Bull Seismol Soc Am 106:2136–2153, 〈span〉2016〈/span〉) (GP2016) with the multiple asperity characterization approach of Irikura and Miyake (Pure Appl Geophys 168:85–104, 〈span〉2011〈/span〉) (IM2011, also known as Irikura recipe). The rupture generator uses a multi-scale hybrid approach that incorporates distinct features of both original approaches, such as small-scale stochastic rupture variability and depth-dependent scaling of rupture speed and slip rate, inherited from GP2016, and specification of discrete high slip rupture patches, inherited from IM2011. The performance of the proposed method is examined in simulations of broadband ground motion from the 2016 Kumamoto, Japan earthquake, as well as comparisons with ground motion prediction equations (GMPEs). We generated rupture models with multi-scale heterogeneity, including a hybrid one in which the slip is a combination of high- slip patches and stochastic small scale variations. We find that the ground motions simulated with these rupture models match the general characteristics of the recorded near-fault motion equally well, over a broad frequency range (0–10 Hz). Additionally, the simulated ground motion is in good agreement with the predictions from Ground Motion Prediction Equations (GMPEs). Nonetheless, due to sensitivity of the ground motion to the local fault rupture characteristics, the performance among the models at near-fault sites is slightly different, with the hybrid model producing a somewhat better fit to the recorded ground velocity waveforms. Sensitivity tests of simulated near-fault ground motion to variations in the prescribed kinematic rupture parameters show that average rupture speeds higher than the default value in GP2016 (average rupture speed = 80% of local shear wave speed), as well as slip rate durations shorter than the default value in GP2016 (rise time coefficient = 1.6), generate ground motions that are higher than the recorded ones at periods longer than 1 s. We found that these two parameters also affect the along strike and updip rupture directivity effects, as illustrated in comparisons with the Kumamoto observations.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The three-dimensional Massachusetts Institute of Technology general circulation model (MITgcm) with time-dependent forcing is implemented to investigate the spatial and temporal variability of internal tides over the eastern coast of India. Numerical simulations are conducted for a number of different months of the year for which in situ observations are available at high temporal resolution. During the months of November–December and March–April, peak spectral estimates of density variability are evident in the semidiurnal frequency band in both observations and simulations, while during August, variability is dominantly in the near-inertial frequency band. Empirical orthogonal functions (EOF) analysis is applied to decompose the baroclinic tidal currents into vertical modes. The results show that about 70–80% of the total variance is in the first mode, while the first three modes represent 90–95% of the total variance in all seasons. Internal tide characteristics such as phase speed, group speed, and wavelength are largest in the postmonsoon season. The magnitude of the computed energy flux is greatest during November, while the direction of propagation of internal tides is almost unchanged through the year. The available potential energy peaks in November (20 kJ m〈sup〉−2〈/sup〉) and is smallest in August (14 kJ m〈sup〉−2〈/sup〉). Calculation of the energy budget shows that the energy conversion rate from barotropic forcing to internal tides is about 85% in November but only about 46% in August.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In the Garhwal Himalayan Corridor (GHC), we recorded the magnetotelluric (MT) data at 40 sites, in three phases. Out of these 40 sites, useful tipper or vertical magnetic field transfer function (VTF) data was available only at 19 sites. The resistivity model, obtained from 3D inversion of the MT data, is used to investigate the existence of transverse tectonic structures in the Garhwal Himalaya. Through a synthetic inversion experiment on scattered data over a profile, like our GHC profile, we have demonstrated that the MT data can be used to qualitatively infer about the off-profile resistivity structures within about 20 km from the profile. We carried out several 3D inversion experiments using different subsets of full impedance tensor and VTF responses individually and jointly to arrive at the final resistivity model. The 2D profile section of our 3D resistivity model explains the thrust tectonic and 〈em〉flat ramp flat〈/em〉 geometry of the Main Himalayan Thrust (MHT). Furthermore, the inverted model delineated Delhi–Haridwar Ridge (DHR) as a highly resistive (〉 1000 Ωm) feature beneath the low resistive (〈 50 Ωm) sediments of the Indo-Gangetic Plain (IGP). The DHR continues up to the Inner Lesser Himalayan region, and it is bounded by two conductive (〈 10 Ωm) fluid-saturated fractured zones situated off-profile, and these run nearly parallel to the DHR. From the electrical image of the DHR and of the associated conducting feature, which have the geoelectric strike of N13°E, we inferred that these features are transverse to the main Himalayan arc.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉This paper describes a validated dynamic rupture model of the 2011 Tohoku earthquake that reproduces both long-period (20–100 s) and short-period (3–20 s) ground motions. In order to reproduce the observed large slip area (slip asperity), we assign a large 〈em〉D〈/em〉〈sub〉c〈/sub〉 (slip critical distance) area following kinematic source inversion results. Sufficiently large slip is achieved through rupture reactivation by the double-slip-weakening friction model. In order to reproduce the strong-motion generation areas (SMGAs), we assign short 〈em〉D〈/em〉〈sub〉c〈/sub〉 and large stress-drop areas following empirical Green’s function (EGF) simulation results, which indicate that, although more distant from the hypocenter, SMGA1 ruptured earlier than SMGA2 or SMGA3, which are closer to the hypocenter. This observation is confirmed by the backprojection method. In order to reproduce this important feature in dynamic simulation results, we introduce a chain of small high stress-drop patches between the hypocenter and SMGA1. By systematic adjustment of stress drops and 〈em〉D〈/em〉〈sub〉c〈/sub〉, the rupture reproduces the observed sequence and timing of SMGA ruptures and the final slip derived by kinematic models. This model also reproduces the multiseismic wavefront observed from strong ground motion data recorded along the Pacific coast of the Tohoku region. We compare the velocity waveforms recorded at rock sites along the coastline with one-dimensional (1D) synthetic seismograms for periods of 20–100 s. The fit is very good at stations in the northern and central areas of Tohoku. We also perform finite-difference method (FDM) simulations for periods of 3–20 s, and confirm that our dynamic model also reproduces wave envelopes. Overall, we are able to validate the rupture process of the Tohoku earthquake.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Earthquakes have caused tremendous damage in China and around the world; the Wenchuan earthquake that occurred in China 10 years ago is among the deadliest earthquakes in history. The importance of earthquake monitoring and seismic data analysis is now recognized in China. However, the effective dissemination of earthquake-related disaster risk reduction (DRR) knowledge to decision-makers and the public has not been adequately addressed. Under the auspices of the United Nations Educational, Scientific, and Cultural Organization (UNESCO), the International Knowledge Centre for Engineering Science and Technology (managed by the Chinese Academy of Engineering) launched the Disaster Risk Reduction Knowledge Service in 2016. This service, based on the development of disaster metadata standards, was constructed to share disaster information and provide thematic knowledge services; it facilitates the integration and sharing of disaster data, disaster maps, expert opinions, institutional knowledge, research literature, and videos. A series of earthquake DRR knowledge services applications have been implemented using this knowledge service platform, including (1) a global earthquake daily distribution map service, (2) a spatiotemporal map of historical earthquakes in the One Belt One Road region, (3) a Wenchuan earthquake disaster relief knowledge service, and (4) a thematic knowledge service for disaster relief work and contingency planning during the Jiuzhaigou earthquake. In the long term, this system will support the conversion of disaster data into DRR knowledge and provide services for international organizations, government institutions, research and educational institutions, enterprises, and the general public.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Serpentine is formed by hydrothermal metasomatism and may penetrate into the deep crust or mantle of the Earth. It is considered to be the water resource of the mantle owing to its high water content and high-temperature decomposition (600–900 °C). In some geological settings, it has low wave velocity (lower than that of the surrounding rocks) and high electrical conductivity (higher than that of the surrounding rocks), which are the universal physical and geological properties of serpentine found across continents on Earth. Studying the properties of this layer, in particular the wave velocity and electrical conductivity, contributes to a more in-depth understanding of the mid-lower crust or mantle of the Earth. It is also helpful for exploring the mechanism of seismicity owing to the relationship of this layer with the earthquake center location. In subduction zones, the stability of serpentine is a factor affecting seismicity. In this study, the wave velocity and electrical conductivity data for serpentine, together with temperature and pressure, have been collated from previous studies. Some of these studies provide more comprehensive results and others provide new conclusions. Overall, the findings showed that a low-wave-velocity and high-electrical-conductivity layer can be found in serpentine under suitable geological settings. Details of the driving mechanism behind seismicity in subduction zones are also shown.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Remote-sensing techniques are currently the only means of collecting information to monitor the atmospheric dynamics of lightning from the regional to the national scales, allowing for the generation of homogeneous and long time series. Attempts to characterize the impacts of atmospheric discharge in Brazil presuppose an understanding of spatial and temporal lightning patterns. Despite the high frequency of lightning and significant disturbances caused in highly populated regions such as the metropolitan region of Rio de Janeiro (MRRJ), these phenomena are not well characterized when using a long-term contemporaneous dataset. Accordingly, this work focuses on the spatial and temporal variability of cloud-to-ground lightning in the metropolitan region of Rio de Janeiro, an area affected by a high level of atmospheric discharge every year. We performed a statistical analysis of lightning data taken from a lightning location system for the 16-year period of 2001–2016 and analysed characteristics such as polarity, peak currents, geographic distributions and diurnal, intra- and inter-annual variability. Extremely high levels of high activity were observed from 258,794 cloud-to-ground lightning events recorded over the analysed period and for 64.3% events occurring in summer, 20.5% events occurring in spring and 12.9%, and 2.3% events occurring in autumn and winter. The discharge events were predominantly negative (93.54% of the total). Peak levels of electrical activity were observed from roughly 18:00 to 19:00 local time, when there is more potential energy available for convection. The results of the spatial analysis reveal that most lightning observed over Rio de Janeiro derived from the orographic effect, which spurs the formation of convective storms along the southern part of the slope.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The moisture river (MR) concept is used here to revisit the characteristics of moisture transport during the Indian Summer Monsoon (ISM) season from June to September. The study is carried out using Modern-Era Retrospective analysis for Research and Applications (MERRA) data products for the 30-year period from 1982 to 2011. MRs are detected from vertically integrated vapor transport (IVT) computed using validated MERRA mixing ratios and horizontal wind speeds at vertical levels from the surface to 300 hPa. The characteristics of MR and moisture transport associated with major rainfall episodes of the 2011 ISM are studied in detail. The large moisture content, together with high wind speeds associated with the monsoon low-level jet, contributes to the observed structure of the MR. The outflux of moisture from the Arabian Sea is on average 40% larger than the cross-equatorial flux from the southern Indian Ocean, indicating increased contribution from the Arabian Sea. The upward movement of moisture to the layers above the jet is a decisive factor in the strengthening of the river and major rainfall episodes. Back-trajectory analyses reveal that the path of moisture transport from the southern Indian Ocean is confined to the lower levels, whereas higher-level trajectories originate from the Red Sea, Arabian Sea and southern Indian Ocean. The MR statistics show significant intra-seasonal and inter-annual variability in occurrence and strength, with a near-linear relationship between the IVT strength and the corresponding daily ISM rainfall, especially over the west coast. Wavelet cross-spectral analyses carried out using the daily Arabian Sea IVT maximum and rainfall over the west coast and central India during a deficit and surplus monsoon year depict significant differences in the dominant periodicities, associated with intra-seasonal and inter-annual monsoon variations.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The high-frequency decay parameter kappa (〈em〉κ〈/em〉) was computed by fitting Fourier amplitude spectra from the seismic network of the Taiwan Strong Motion Instrumentation Program (TSMIP). The κ of shear horizontal waves (SH waves) was calculated for individual recordings, and the relationship between κ values and the epicentral distance (〈em〉R〈/em〉〈sub〉epi〈/sub〉) of each station was derived for each station. The κ value at 〈em〉R〈/em〉〈sub〉epi〈/sub〉 = 0 (denoted as 〈em〉κ〈/em〉〈sub〉0〈/sub〉) can be used as a site parameter. There are totally 26,277 seismograms that have been recorded at 679 TSMIP stations over the period of 1993 through 2014 with local magnitudes of 4.0–7.1 and focal depths less than 30 km. The estimation of 〈em〉κ〈/em〉〈sub〉0〈/sub〉 for Taiwan ranges from 0.0208 to 0.147 s, and the spatial distribution of 〈em〉κ〈/em〉〈sub〉0〈/sub〉 was closely related to geology and velocity. The site-specific 〈em〉κ〈/em〉〈sub〉0〈/sub〉 values from 425 stations were correlated with the averaged shear wave velocity of the top 30 m of strata (〈em〉V〈/em〉〈sub〉S30〈/sub〉), and the relationship could be described as 〈em〉κ〈/em〉〈sub〉0〈/sub〉 = (0.125 ± 0.005) − (0.011 ± 0.001) × ln(〈em〉V〈/em〉〈sub〉S30〈/sub〉), and an acceptable linear correlation (〈em〉R〈/em〉〈sup〉2〈/sup〉 = 0.57) was performed. The results may be used in the future application of ground motion prediction equations (GPMEs) and serve as simulation parameters. Also, the relationship between 〈em〉κ〈/em〉〈sub〉0〈/sub〉 and the depth to engineering rock (〈em〉Z〈/em〉〈sub〉1.0〈/sub〉) is not well correlated, whereas an acceptable correlation exists between 〈em〉κ〈/em〉〈sub〉0〈/sub〉 and other site proxies (i.e., elevation and resonant frequency).〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Examines the state in the field of earthquake prediction and modern views of geomechanics on the nucleation of foci of strong earthquakes. From the point of view of tectonophysics, the problem of the mechanism of mega-earthquake occurrence is considered. It is shown that data obtained by tectonophysics methods on the natural stress magnitudes in regions with the strongest twenty-first century earthquakes are the key to its solution. Results of tectonophysical stress inversion define the main area of the mega-earthquake focus as an extended area of low and medium magnitudes of stress. This result corresponds to geomechanical concepts indicating that the state of earthquake focus depends on the Rate and State theory of friction. Numerical geomechanical calculation shows that before the formation of a large-scale brittle fracture, the fault weakens, which manifests in the acceleration of aseismic slip. In real rock, the processes of strength reduction due to increasing aseismic displacement can take years, many decades, and perhaps even centuries. Tectonophysical analysis of natural stress shows that the nucleation of an earthquake can occur both from the boundary of the focus and inside of the focus. In both cases, this small area should be a zone of high stress.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Seismic resonance inside sedimentary basins severely influences ground shaking at the free surface in case of earthquakes. Starting from few observations of a low-frequency resonance in the historical center of Rome, Italy, we performed several single-station ambient vibration measures to verify and estimate the resonance frequency in a wide area of the city by Horizontal-to-Vertical spectral ratio method. We verified a stable low-frequency peak in the range 0.3–0.4 Hz. Recordings of August 24th 2016, Mw 6.0 Amatrice earthquake, available both inside and outside the basin of Rome, confirm the presence of high-energy components at frequencies of 0.2–0.4 Hz within the basin. These observations support the hypothesis of a deep seismic impedance contrast responsible for the low frequency resonance. To infer the depth range of subsoil deposits related to this impedance contrast, we analyzed ambient vibration data recorded by 2-D seismic arrays aiming at retrieving the shear-wave velocity structure up to relevant depths. To increase the investigation depth (up to 2000 m), we jointly inverted for Rayleigh-waves dispersion and ellipticity curves and resonance frequency. The shear-wave velocity profile shows two main discontinuities at depths of about 500 m and 1800 m that can be related to the bottom of the Plio-Pleistocene filling of the Rome basin and to the top of the basal limestone formation, respectively. These results fill a gap of knowledge about the deep velocity structure in the city that may be helpful for ground-motion scenario studies.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Sea level and sea surface temperature inter-annual variability and trends in the Mediterranean Sea were investigated during the period 1993–2017. These were carried out using gridded absolute dynamic topography from satellite altimetry, tide gauge (TG) time series from 25 stations and gridded sea surface temperature (SST) from advanced very-high-resolution radiometer (AVHRR) data. The coastal TG data were used to verify the satellite derived sea level. Moreover, the contributions of atmospheric pressure and North Atlantic Oscillation (NAO) to sea level changes were also examined. The results revealed that the Mediterranean Sea exhibits inter-annual spatiotemporal coherent variability in both sea level and SST. The spatial variability in sea level is more significant over the Adriatic and Aegean Seas, most of the Levantine basin, and along the Tunisian shelf. Marked spatial variability in SST occurs over the central part of the Mediterranean Sea with maximum amplitude in the Tyrrhenian Sea. The highest temporal variability of sea level and SST was found in 2010 and 2003, respectively. The inter-annual variability of sea level and SST accounts for about 32% and 3% of the total variance of sea level and SST, respectively. An analysis of sea level anomaly reveled large negative values during the extended winter of 2011–2012, which may be attributed to the strong positive phase of NAO index. Satellite altimetry indicated a significant positive sea level trend of 2.7 ± 0.41 mm/year together with a significant warming of 0.036 ± 0.003 °C/year over the whole Mediterranean Sea for the period 1993–2017.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In the exploration and production of fossil resources, the characterization of rock facies is critical for estimations of rock physical properties, such as porosity and permeability, and for reservoir detection and simulation. We propose a new machine learning (ML) algorithm for characterizing rock facies using a convolutional neural network (CNN) with feature engineering and data padding strategies. In the new ML algorithm, we extend rock feature data from 1-dimensional “profile” to 2-dimensional maps by padding the original dataset. The 2-dimensional padded rock facies map enables the CNN to capture the inherent geological features while keeping the local continuities. In this new ML algorithm, we only need a simple CNN design and structure to efficiently achieve accurate classification of rock facies. We test the feasibility of applying this new algorithm using a verifiable well logging dataset from the Panoma gas field in southwest Kansas. The results show that our new ML algorithm with a simple CNN structure has achieved higher accuracy in classifications of rock facies in comparison with the CNN results of the 2016 SEG ML contest. This new ML algorithm has application potential in automatic rock facies characterization with high accuracy and efficiency.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉On July 20, 2017 22:31 UTC, a strong M〈sub〉w〈/sub〉 = 6.6 earthquake occurred at shallow depth between Kos Island (Greece) and Bodrum (Turkey). We derive a co-seismic fault model from joint inversion of geodetic data (GNSS and InSAR) assuming that the earthquake can be modelled by the slip of a rectangular fault buried in an elastic and homogeneous half-space. The GNSS observations constrain well most of the model parameters but do not permit to discriminate between south- and north-dipping planes. However, the interferograms, produced from C-band ESA Sentinel 1 data, give a clear preference to the north-dipping plane. We also map surface motion away from the satellite along the Turkish coast (from Bodrum towards the east) which reached about 17 cm onshore islet Karaada. The best-fit model is obtained with a 37° north-dipping, N283°E striking normal fault, in agreement with the published moment tensor solutions. The resolved slip vector is dominantly normal with a slight component of left-lateral motion (15°). The surface projection of the seismic fault outcrops in the Gökova ridge area, a well-developed bathymetric feature inside the western Gulf of Gökova. Our geodetic model fits the pattern of the shallow, north-dipping aftershocks obtained from rigorous relocation of all available recordings in the region (about 1120 events; relocated mainshock is at 36.955°N, 27.448°E; depth at 9.2 km ± 0.5 km). The relocated aftershocks also indicate clustering at both ends of the rupture and seismicity triggering mainly towards the east and the north, within 2 weeks following the mainshock. We also analysed regional GPS data (interseismic velocities) and obtained an extension rate of 3.2 mm/yr across the Gökova rift, along a direction N165°E.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Seismic and rock burst hazard is a very important factor that has to be considered in seismically active mining areas. Several different methods are used to decrease seismic activity in mines. Among others, an active prevention method known as destress blasting, is considered the most effective technique. The aim of this work is to find possible influences of such active prevention on observed seismic activity recorded in the established waiting time after blasts. Using technological knowledge and seismic data recorded by an underground seismic network, we estimated several parameters that characterize sources provoked by blasting works and compared them with the parameters obtained for spontaneous, non-provoked mining tremors. According to our studies the source mechanisms of post-blasting seismicity are characterized by the similar non-DC part of the full moment tensor whereas the source mechanisms of spontaneous events are not characterized by any specific features. On the other hand non-provoked seismicity presents lowest values of apparent stress. Also E〈sub〉S〈/sub〉 to E〈sub〉P〈/sub〉 ratio suggest some differences between events occurred immediately after blasting (up to 30 s) and the rest dataset. We believe that these parameters could be considered valuable tools supporting established safety time limitations after active prevention.〈/p〉