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  • 1
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    Quick determination of earthquake source parameters from GPS measurements: a study of suitability for Taiwan (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉We test the feasibility of GPS-based rapid centroid moment tensor (GPS CMT) methods for Taiwan, one of the most earthquake prone areas in the world. In recent years, Taiwan has become a leading developer of seismometer-based earthquake early warning systems, which have successfully been applied to several large events. The rapid determination of earthquake magnitude and focal mechanism, important for a number of rapid response applications, including tsunami warning, is still challenging because of the limitations of near-field inertial recordings. This instrumental issue can be solved by an entirely different observation system: a GPS network. Taiwan is well posed to take advantage of GPS because in the last decade it has developed a very dense network. Thus, in this research, we explore the suitability of the GPS CMT inversion for Taiwan. We retrospectively investigate six moderate to large (〈span〉M〈/span〉〈sub〉w〈/sub〉6.0 ∼ 7.0) earthquakes and propose a resolution test for our model, we find that the minimum resolvable earthquake magnitude of this system is ∼〈span〉M〈/span〉〈sub〉w〈/sub〉5.5 (at 5 km depth). Our tests also suggest that the finite fault complexity, often challenging for the near-field methodology, can be ignored under such good station coverage and thus, can provide a fast and robust solution for large earthquake directly from the near field. Our findings help to understand and quantify how the proposed methodology could be implemented in real time and what its contributions could be to the overall earthquake monitoring system.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
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    Quick Determination of Earthquake Source Parameters from GPS Measurements: A Study of Suitability for Taiwan (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Summary〈/div〉We test the feasibility of GPS-based rapid centroid moment tensor (GPS CMT) methods for Taiwan, one of the most earthquake prone areas in the world. In recent years Taiwan has become a leading developer of seismometer-based earthquake early warning systems which have successfully been applied to several large events. The rapid determination of earthquake magnitude and focal mechanism, important for a number of rapid response applications, including tsunami warning, is still challenging because of the limitations of near-field inertial recordings. This instrumental issue can be solved by an entirely different observation system: a GPS network. Taiwan is well-posed to take advantage of GPS because in the last decade it has developed a very dense network. Thus, in this research, we explore the suitability of the GPS CMT inversion for Taiwan. We retrospectively investigate six moderate to large (M〈sub〉w〈/sub〉6.0∼7.0) earthquakes and propose a resolution test for our model, we find that the minimum resolvable earthquake magnitude of this system is ∼M〈sub〉w〈/sub〉5.5 (at 5 km depth). Our tests also suggest that the finite fault complexity, often challenging for the near-field methodology, can be ignored under such good station coverage and thus, can provide a fast and robust solution for large earthquake directly from the near-field. Our findings help to understand and quantify how the proposed methodology could be implemented in real-time and what its contributions could be to the overall earthquake monitoring system.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
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    A Global Database of Strong‐Motion Displacement GNSS Recordings and an Example Application to PGD Scaling (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉ABSTRACT〈/div〉Displacement waveforms derived from Global Navigation Satellite System (GNSS) data have become more commonly used by seismologists in the past 15 yrs. Unlike strong‐motion accelerometer recordings that are affected by baseline offsets during very strong shaking, GNSS data record displacement with fidelity down to 0 Hz. Unfortunately, fully processed GNSS waveform data are still scarce because of limited public availability and the highly technical nature of GNSS processing. In an effort to further the use and adoption of high‐rate (HR) GNSS for earthquake seismology, ground‐motion studies, and structural monitoring applications, we describe and make available a database of fully curated HR‐GNSS displacement waveforms for significant earthquakes. We include data from HR‐GNSS networks at near‐source to regional distances (1–1000 km) for 29 earthquakes between Mw 6.0 and 9.0 worldwide. As a demonstration of the utility of this dataset, we model the magnitude scaling properties of peak ground displacements (PGDs) for these events. In addition to tripling the number of earthquakes used in previous PGD scaling studies, the number of data points over a range of distances and magnitudes is dramatically increased. The data are made available as a compressed archive with the article.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 4
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    Ground Motions from the 7 and 19 September 2017 Tehuantepec and Puebla‐Morelos, Mexico, Earthquakes (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Abstract〈/div〉The 2017 M 8.2 Tehuantepec and M 7.1 Puebla‐Morelos earthquakes were deep inslab normal‐faulting events that caused significant damage to several central‐to‐southern regions of Mexico. Inslab earthquakes are an important component of seismicity and seismic hazard in Mexico. Ground‐motion prediction equations (GMPEs) are an integral part of seismic hazard assessment as well as risk and rapid‐response products. This work examines the observed ground motions from these two events in comparison to the predicted median ground motions from four GMPEs. The residuals between the observed and modeled ground motions allow us to study regional differences in shaking, the effects of each earthquake, and basin effects in Mexico City, Puebla, and Oaxaca. We find that the ground motions from these two earthquakes are generally well modeled by the GMPEs. However, the Tehuantepec event shows larger than expected ground motions at greater distances and longer periods, which suggests a waveguide effect from the subduction zone geometry. Finally, Mexico City and the cities of Puebla and Oaxaca exhibit very large ground motions, indicative of well‐known site and basin effects that are much stronger than the basin terms included in some of the GMPEs. Simple and rapid ground‐motion parameter estimates that include site effects are key for hazard and real‐time risk assessments in regions such as Mexico, where the vast majority of the population lives in areas where the aforementioned effects are relevant. However, GMPEs based on site correction terms dependent on topographic slope proxies underestimate, at least in the three cities tackled in this work, the observed amplification. Therefore, there is a need to improve models of seismic amplification in basins that could be included in GMPEs.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 5
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    A Global Database of Strong‐Motion Displacement GNSS Recordings and an Example Application to PGD Scaling (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉ABSTRACT〈/div〉Displacement waveforms derived from Global Navigation Satellite System (GNSS) data have become more commonly used by seismologists in the past 15 yrs. Unlike strong‐motion accelerometer recordings that are affected by baseline offsets during very strong shaking, GNSS data record displacement with fidelity down to 0 Hz. Unfortunately, fully processed GNSS waveform data are still scarce because of limited public availability and the highly technical nature of GNSS processing. In an effort to further the use and adoption of high‐rate (HR) GNSS for earthquake seismology, ground‐motion studies, and structural monitoring applications, we describe and make available a database of fully curated HR‐GNSS displacement waveforms for significant earthquakes. We include data from HR‐GNSS networks at near‐source to regional distances (1–1000 km) for 29 earthquakes between Mw 6.0 and 9.0 worldwide. As a demonstration of the utility of this dataset, we model the magnitude scaling properties of peak ground displacements (PGDs) for these events. In addition to tripling the number of earthquakes used in previous PGD scaling studies, the number of data points over a range of distances and magnitudes is dramatically increased. The data are made available as a compressed archive with the article.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 6
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    A Method for Rapid Estimation of Moment Magnitude for Early Tsunami Warning Based on Coastal GPS Networks (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-05-01
    Description: INTRODUCTION The recent great earthquakes of 26 December 2004 (Sumatra, Indonesia, Mw 9.2), 26 February 2010 (Maule, Chile, Mw 8.8), and 11 March 2011 (Tohoku-oki, Japan, Mw 9.0) have once again brought to the forefront the urgent need for early tsunami warning. These warnings mostly rely on magnitude and location of an earthquake. A large/great magnitude subduction-zone earthquake with rupture area extending up to the trench is potentially a tsunamigenic event. The appropriate magnitudes for tsunami warning are those that are based on long-period seismic waves (Abe 1979), e.g., the moment magnitude, Mw (Kanamori 1977). Recently, W-phase (the long-period wave that arrives between P and S waves) has been used to compute Mw (Kanamori and Rivera 2008; Hayes et al. 2009). This magnitude can be determined in a relatively short time. For example, the first moment tensor solutions of the Tohoku-oki earthquake, based on inversion of W-phase at teleseismic distances, became available in 20 min (Duputel et al. 2011). For this reason, Mw computed from W-phase is especially useful for tsunami alerts at distant sites. It is at local distances that early tsunami warning becomes difficult. Even then, Mw based on inversion of W-phase recorded at regional distances may be useful. Tests show that Mw of Mexican subduction thrust earthquakes, based on W-phase recorded on broadband, regional seismograms, can be estimated in ∼7 min after the occurrence of the event (Pérez-Campos et al. 2010). In recent years there has been an increase in GPS stations along the coastal region of some subduction zones. Some of these stations are operated in continuous mode (either in real-time high-rate mode or periodic low-rate download mode), and others in campaign mode. Static displacement vectors obtained from GPS data...
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 7
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    Differences between heterogenous and homogenous slip in regional tsunami hazards modelling (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Summary〈/div〉The homogenous slip finite fault model is commonly used in tsunami hazards for a variety of applications. These include early warning and short-term forecasts of tsunami amplitudes, scenario ruptures for risk assessments, and probabilistic tsunami hazard analysis (PTHA). Over the last decade, however, it has become feasible to calculate stochastic slip models which reflect the expected spatial statistics of slip observed in real events. In this paper we examine the impacts of the homogenous slip model when compared to stochastic slip distributions and ask whether, in light of these technical advancements, the homogenous slip assumption remains a reasonable one. We employ a simplified subduction zone geometry, free of complex path and site effects, and study simulated tsunamis from earthquakes in the magnitude 7 to magnitude 9 range. We find that homogenous slip models have lower tsunami potential energies and frequently underpredict the peak tsunami amplitudes and the resulting tsunami hazard, particularly at low probabilities of exceedance. This finding has important implications for all tsunami hazards applications. Calculating a suite of realistic stochastic slip distributions is now within reach of tsunami scientists, thus, we conclude that use of heterogeneous slip models for tsunami hazards applications is preferable〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Ground Motions from the 7 and 19 September 2017 Tehuantepec and Puebla‐Morelos, Mexico, Earthquakes (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Abstract〈/div〉The 2017 M 8.2 Tehuantepec and M 7.1 Puebla‐Morelos earthquakes were deep inslab normal‐faulting events that caused significant damage to several central‐to‐southern regions of Mexico. Inslab earthquakes are an important component of seismicity and seismic hazard in Mexico. Ground‐motion prediction equations (GMPEs) are an integral part of seismic hazard assessment as well as risk and rapid‐response products. This work examines the observed ground motions from these two events in comparison to the predicted median ground motions from four GMPEs. The residuals between the observed and modeled ground motions allow us to study regional differences in shaking, the effects of each earthquake, and basin effects in Mexico City, Puebla, and Oaxaca. We find that the ground motions from these two earthquakes are generally well modeled by the GMPEs. However, the Tehuantepec event shows larger than expected ground motions at greater distances and longer periods, which suggests a waveguide effect from the subduction zone geometry. Finally, Mexico City and the cities of Puebla and Oaxaca exhibit very large ground motions, indicative of well‐known site and basin effects that are much stronger than the basin terms included in some of the GMPEs. Simple and rapid ground‐motion parameter estimates that include site effects are key for hazard and real‐time risk assessments in regions such as Mexico, where the vast majority of the population lives in areas where the aforementioned effects are relevant. However, GMPEs based on site correction terms dependent on topographic slope proxies underestimate, at least in the three cities tackled in this work, the observed amplification. Therefore, there is a need to improve models of seismic amplification in basins that could be included in GMPEs.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 9
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    The 19 September 2017 M 7.1 Puebla‐Morelos Earthquake: Spectral Ratios Confirm Mexico City Zoning (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Abstract〈/div〉One important element of understanding basin response to strong shaking is the analysis of spectral ratios, which may provide information about the dominant frequency of ground motion at specific locations. Spectral ratios computed from accelerations recorded by strong‐motion stations in Mexico City during the mainshock of the 19 September 2017 M 7.1 Puebla‐Morelos earthquake reveal predominate periods consistent with those mapped in the 2004 Mexican seismic design code. Furthermore, the predominant periods thus computed validate those studies using mainshock and aftershock recordings of the handful strong‐motion stations that recorded the 19 September 1985 M 8.1 Michoacán earthquake. Even though the number of stations in each of the zones (zones I, II, IIIa, b, c, and d) is not the same, they still allow confirmation of site frequencies (periods) attributable to the specific zones (particularly those in zones IIIa, b, c, and d). Spectral ratios are computed with two different methods: (1) horizontal to horizontal (H/H) ratio of smoothed amplitude spectrum of a horizontal channel in direction X of a station with respect to the smoothed amplitude spectrum of the horizontal channel in the same X direction of a reference stiff soil (or rock) station and (2) horizontal to vertical (H/V) ratio (or also known as the Nakamura method) of both horizontal (H) and vertical (V) channels of the same station. We show a comparison of the identified frequencies (periods) derived by both methods and find they are very similar and in good agreement with those indicated in the zoning maps of Mexico City in the 2004 seismic design code.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 10
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    Seismogeodesy Using GPS and Low-Cost MEMS Accelerometers: Perspectives for Earthquake Early Warning and Rapid Response (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-12-02
    Description: The seismogeodetic method computes accurate displacement and velocity waveforms by optimally extracting high-frequency information from strong-motion accelerometers and low-frequency information from collocated Global Positioning System (GPS) instruments. These broadband observations retain the permanent (static) displacement, are immune to clipping and magnitude saturation for large earthquakes, and are sensitive enough to record P -wave arrivals. These characteristics make seismogeodesy suitable for real-time applications such as earthquake early warning. The Scripps Institution of Oceanography (SIO) has developed an inexpensive microelectromechanical systems (MEMS) accelerometer package to upgrade established GPS stations. We compare the performance of our MEMS accelerometer with an observatory-grade accelerometer using an experiment at the University of California San Diego Large High-Performance Outdoor Shake Table. We show that the two types of accelerometers agree in frequency ranges of seismological and engineering interest and produce equivalent seismogeodetic estimates of displacement and velocity. To date, 27 SIO MEMS packages have been installed at GPS monitoring stations in southern California and the San Francisco Bay area and have recorded four earthquakes ( M  4.2, M  4.1, and two of M  4.0). The P -wave arrivals are distinguishable in the seismogeodetic observations at distances of up to ~25 km away but not in the GPS-only displacements. There is no significant permanent deformation for these small events. This study demonstrates the lower limit of detectability and that seismogeodetic waveforms can also be a reliable early confirmation that an event is not large or hazardous. It also raises the possibility of rapid magnitude estimation through scaling relationships.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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