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  • 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous  (6)
  • Climate-change ecology  (2)
  • SSA  (5)
  • Nature Publishing Group  (3)
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Keywords
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  • 1
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    Effect of time-dependence on probabilistic seismic hazard maps and deaggregation for the central apennines, Italy (2008)
    SSA
    Details
    Publication Date: 2017-04-04
    Description: We produce probabilistic seismic hazard assessments for the Central Apennines, Italy, using time-dependent models that are characterized using a Brownian Passage Time (BPT) recurrence model. Using aperiodicity parameters,  of 0.3, 0.5, and 0.7, we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters. For the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults. We use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault (floating fault model) to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation. We show maps for peak ground acceleration (PGA) and 1.0-Hz spectral acceleration (SA1) on rock having 10% probability of exceedence (PE) in 50 years. We produce maps to compare the separate contributions of smoothed seismicity and fault components. In addition we construct maps that show sensitivity of the hazard for different  parameters and the Poisson model. For the Poisson model, the addition of fault sources to the smoothed seismicity raises the hazard by 50 % at locations where the smoothed seismicity contributes the highest hazard, and up to 100 % at locations where the hazard from smoothed seismicity is low. For the strongest aperiodicity parameter (smallest ), the hazard may further increase 60-80 % or more or may decrease by as much as 20 %, depending on the recency of the last event on the fault that dominates the hazard at a given site. In order to present the most likely earthquake magnitude and/or the most likely source-site distance for scenario studies, we deaggregate the seismic hazard for SA1 and PGA for two important cities (Roma and l’Aquila) . For PGA, both locations show the predominance of local sources, having magnitudes of about 5.3 and 6.5 respectively. For SA1 at a site in Rome, there is significant contribution from local smoothed seismicity, and an additional contribution from the more distant Apennine faults having magnitude around 6.8. For l’Aquila, the predominant sources remain local. In order to show the variety of impact of different  values we also obtained deaggregations for another three sites. In general, as  decreases (periodicity increases), the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates. This effect is strongest for the long-period (1 s) ground motions.
    Description: In press
    Description: 4.2. TTC - Scenari e mappe di pericolosità sismica
    Description: JCR Journal
    Description: open
    Keywords: Time dependent ; Deaggregations ; Central Apennines, Italy ; Uncertainties ; Aperiodicity ; PSHA ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Evidence for Great Tsunamigenic Earthquakes (M8.6) along the Mexican Subduction Zone (2009)
    SSA
    Details
    Publication Date: 2017-04-04
    Description: A very large earthquake took place on 28 March 1787 along the Mexican subduction zone. A unique characteristic of the 1787 event is the large tsunami reported at various coastal locations in southern Mexico. The segment of the coast affected by the strong tsunami coincides with locations where high felt intensities (modified Mercalli intensity [MMI] 〉VIII) were reported. Assuming, as is generally the case for large and great earthquakes in Mexico, that the fault rupture of the 1787 earthquake encompasses the areas where intensities greater than VIII were reported and where a strong tsunami invaded land, the estimated length of the rupture is approximately 450 km long. This fault length would correspond to an earthquake of approximately Mw 8.6. In the instrumental record there is no evidence of earthquakes of this magnitude in the Middle American subduction zone. This evidence indicates that the rupture area of the 1787 earthquake was at least three times longer that those normally observed for earthquakes that take place in the Mexican subduction zone. The 1787 earthquake appears to have ruptured a long fault segment that more recently broke in earthquakes of more moderate magnitude (Mw 7–8) and relatively short recurrence times of about 30 to 40 yr. Examples of this mode of variable rupture length where great but infrequent earthquakes rupture the fault areas of relatively smaller and more frequent earthquakes have been observed in the Sumatra–Andaman and Colombia–Ecuador plate boundaries, among others.
    Description: Published
    Description: 892-896
    Description: 3.10. Storia ed archeologia applicate alle Scienze della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: Mexico ; great tsunamigenic earthquakes ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Evaluation of Deep Sediment Velocity Structure in the New Madrid (2008)
    SSA
    Details
    Publication Date: 2017-04-04
    Description: Detailed knowledge of the physical properties of the sediments filling the Mississippi Embayment has proven critical to both unravel the tectonic framework operating in the region and assess the seismic hazards posed by the New Madrid Seismic Zone. In this article we show that independent geotechnical estimates for Pand S-wave velocities are compatible with a sedimentary model of K-feldspar clasts embeded in water, and we test its validity by modeling receiver functions at a number of broadband stations. By constraining the bulk sediment thicknesses beneath each station from independent reflection profiling estimates, we have been able to recover the depth to the top of the Cretaceous from the receiver function data at individual stations. Our receiver function modeling thus provides confidence in the velocity and density structures extrapolated from in situ geotechnical measurements in the Upper Mississippi Embayment.
    Description: Published
    Description: 334-340
    Description: JCR Journal
    Description: reserved
    Keywords: receiver functions, mississipi embayment ; velocity tructure ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Estimating Absolute Site Effects (2008)
    SSA
    Details
    Publication Date: 2017-04-04
    Description: We use previously determined direct-wave attenuation functions as well as stable, coda-derived source excitation spectra to isolate the absolute S-wave site effect for the horizontal and vertical components of weak ground motion. We use selected stations in the seismic network of the eastern Alps. A detailed regional attenuation function derived by Malagnini et al. (2002) for the region is used to correct the vertical and horizontal S-wave spectra. These corrections account for the gross path effects (i.e., all distance-dependent effects), although the source and site effects are still present in the distance-corrected spectra. The main goal of this study is to isolate the absolute site effect (as a function of frequency) by removing the source spectrum (moment-rate spectrum) from the distance-corrected S-wave spectra. Typically, removing the S-wave source spectrum is difficult because of inadequate corrections for the source radiation pattern, directivity, and random interference. In addition to complexities near the source, 2D and 3D structure beneath the recording site will result in an azimuth-dependent site effect. Since the direct wave only samples a narrow range in takeoff and backazimuth angles, multistation averaging is needed to minimize the inherent scatter. Because of these complicating effects, we apply the coda methodology outlined by Mayeda et al. (2003) to obtain stable moment-rate spectra. This methodology provides source amplitude and derived source spectra that are a factor of 3–4 times more stable than those derived from direct waves. Since the coda is commonly thought of as scattered energy that samples all ray parameters and backazimuths, it is not very sensitive to the source radiation pattern and 3D structure. This property makes it an excellent choice for use in obtaining average parameters to describe the source, site, and path effects in a region. Due to the characteristics of the techniques used in this study, all the inverted quantities are azimuthally averaged, since the azimuthal information is lost in the processing. Our results show that (1) all rock sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0.5 and 12 Hz (the available bandwidth), on both the horizontal and vertical components; (2) rock-site transfer functions showed large variability at high-frequency; (3) vertical-motion site transfer functions show strong frequency dependence; (4) horizontal-to-vertical (H/V) spectral ratios do not reproduce the charactersitics of the true horizontal site transfer functions; and (5) traditional, relative site terms obtained by using reference rock sites can be misleading in inferring the behaviors of true site transfer functions, since most rock sites have nonflat responses due to shallow heterogeneities resulting from varying degrees of weathering. Our stable source spectra are used to estimate the total radiated seismic energy and to compare against similar results obtained for different regions of the world. We find that the earthquakes in this region exhibit nonconstant dynamic stress drop scaling, which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes.
    Description: Published
    Description: 1343-1352
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: site effects ; italy ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Limited overlap between the seismic gap and coseismic slip of the great 2010 Chile earthquake (2011)
    Nature Publishing Group
    Details
    Publication Date: 2017-04-04
    Description: The MW 8.8 mega-thrust earthquake and tsunami that occurred on February 27, 2010, offshore Maule region, Chile, was not unexpected. A clearly identified seismic gap existed in an area where tectonic loading has been accumulating since the great 1835 earthquake experienced and described by Darwin during the voyage of the Beagle. Here we jointly invert tsunami and geodetic data (InSAR, GPS, land-level changes), to derive a robust model for the co-seismic slip distribution and induced co-seismic stress changes, and compare them to past earthquakes and the pre-seismic locking distribution. We aim to assess if the Maule earthquake has filled the Darwin gap, decreasing the probability of a future shock . We find that the main slip patch is located to the north of the gap, overlapping the rupture zone of the MW 8.0 1928 earthquake, and that a secondary concentration of slip occurred to the south; the Darwin gap was only partially filled and a zone of high pre-seismic locking remains unbroken. This observation is not consistent with the assumption that distributions of seismic rupture might be correlated with pre-seismic locking, potentially allowing the anticipation of slip distributions in seismic gaps. Moreover, increased stress on this unbroken patch might have increased the probability of another major to great earthquake there in the near future.
    Description: Published
    Description: 173-177
    Description: 3.1. Fisica dei terremoti
    Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale
    Description: JCR Journal
    Description: restricted
    Keywords: Source process ; Chile ; Tsunami ; Joint Inversion ; Seismic Gap ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.06. Subduction related processes ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Effect of time-dependence on probabilistic seismic hazard maps and deaggregation for the Central Apennines, Italy (2010)
    SSA
    Details
    Publication Date: 2022-06-20
    Description: We produce probabilistic seismic hazard assessments for the Central Apennines, Italy, using time-dependent models that are characterized using a Brownian Passage Time (BPT) recurrence model. Using aperiodicity parameters, of 0.3, 0.5, and 0.7, we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters. For the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults. We use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault (floating fault model) to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation. We show maps for peak ground acceleration (PGA) and 1.0-Hz spectral acceleration (SA1) on rock having 10% probability of exceedence (PE) in 50 years. We produce maps to compare the separate contributions of smoothed seismicity and fault components. In addition we construct maps that show sensitivity of the hazard for different parameters and the Poisson model. For the Poisson model, the addition of fault sources to the smoothed seismicity raises the hazard by 50 % at locations where the smoothed seismicity contributes the highest hazard, and up to 100 % at locations where the hazard from smoothed seismicity is low. For the strongest aperiodicity parameter (smallest ), the hazard may further increase 60-80 % or more or may decrease by as much as 20 %, depending on the recency of the last event on the fault that dominates the hazard at a given site. In order to present the most likely earthquake magnitude and/or the most likely source-site distance for scenario studies, we deaggregate the seismic hazard for SA1 and PGA for two important cities (Roma and l’Aquila) . For PGA, both locations show the predominance of local sources, having magnitudes of about 5.3 and 6.5 respectively. For SA1 at a site in Rome, there is significant contribution from local smoothed seismicity, and an additional contribution from the more distant Apennine faults having magnitude around 6.8. For l’Aquila, the predominant sources remain local. In order to show the variety of impact of different values we also obtained deaggregations for another three sites. In general, as decreases (periodicity increases), the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates. This effect is strongest for the long-period (1 s) ground motions.
    Description: Published
    Description: 585-610
    Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale
    Description: JCR Journal
    Description: open
    Keywords: Time dependent ; Deaggregations ; Central Apennines, Italy ; Uncertainties ; Aperiodicity ; PSHA ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    A reversal of fortunes : climate change ‘winners’ and ‘losers’ in Antarctic Peninsula penguins (2014)
    Nature Publishing Group
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 4 (2014): 5024, doi:10.1038/srep05024.
    Description: Climate change is a major threat to global biodiversity. Antarctic ecosystems are no exception. Investigating past species responses to climatic events can distinguish natural from anthropogenic impacts. Climate change produces ‘winners’, species that benefit from these events and ‘losers’, species that decline or become extinct. Using molecular techniques, we assess the demographic history and population structure of Pygoscelis penguins in the Scotia Arc related to climate warming after the Last Glacial Maximum (LGM). All three pygoscelid penguins responded positively to post-LGM warming by expanding from glacial refugia, with those breeding at higher latitudes expanding most. Northern (Pygoscelis papua papua) and Southern (Pygoscelis papua ellsworthii) gentoo sub-species likely diverged during the LGM. Comparing historical responses with the literature on current trends, we see Southern gentoo penguins are responding to current warming as they did during post-LGM warming, expanding their range southwards. Conversely, Adélie and chinstrap penguins are experiencing a ‘reversal of fortunes’ as they are now declining in the Antarctic Peninsula, the opposite of their response to post-LGM warming. This suggests current climate warming has decoupled historic population responses in the Antarctic Peninsula, favoring generalist gentoo penguins as climate change ‘winners’, while Adélie and chinstrap penguins have become climate change ‘losers’.
    Description: We thank the Zoological Society of London, Quark Expeditions, Exodus Travels ltd., Oceanites, the Holly Hill Charitable Trust, the Charities Advisory Trust and an U.S. National Science Foundation (NSF) Office of Polar Programs grant (ANT-0739575) for funding.
    Keywords: Climate-change ecology ; Molecular ecology ; Molecular evolution ; Population genetics
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 8
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    CO2 and fire influence tropical ecosystem stability in response to climate change (2016)
    Nature Publishing Group
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 6 (2016): 29587, doi:10.1038/srep29587.
    Description: Interactions between climate, fire and CO2 are believed to play a crucial role in controlling the distributions of tropical woodlands and savannas, but our understanding of these processes is limited by the paucity of data from undisturbed tropical ecosystems. Here we use a 28,000-year integrated record of vegetation, climate and fire from West Africa to examine the role of these interactions on tropical ecosystem stability. We find that increased aridity between 28–15 kyr B.P. led to the widespread expansion of tropical grasslands, but that frequent fires and low CO2 played a crucial role in stabilizing these ecosystems, even as humidity changed. This resulted in an unstable ecosystem state, which transitioned abruptly from grassland to woodlands as gradual changes in CO2 and fire shifted the balance in favor of woody plants. Since then, high atmospheric CO2 has stabilized tropical forests by promoting woody plant growth, despite increased aridity. Our results indicate that the interactions between climate, CO2 and fire can make tropical ecosystems more resilient to change, but that these systems are dynamically unstable and potentially susceptible to abrupt shifts between woodland and grassland dominated states in the future.
    Description: This work was supported by NSF grants EAR0601998, EAR0602355, AGS0402010, ATM0401908, ATM0214525, ATM0096232 and AGS1243125 and a Chevron Centennial Fellowship at the University of Texas at Austin awarded to T.M.S.
    Keywords: Climate-change ecology ; Palaeoclimate
    Repository Name: Woods Hole Open Access Server
    Type: Article
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