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  • 1
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    Empirical Mw-ML, mb, and Ms Conversions in Western China (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-12-02
    Description: Local magnitude ( M L ), body-wave magnitude ( m b ), and surface-wave magnitude ( M s ), which are saturated at certain values and may lead to an incorrect energy estimation of a large earthquake, are largely used in quantifying the size of an earthquake in western China. Based on the catalog from the China Earthquake Data Center (CEDC) and moment magnitude ( M w ) provided by the Global Centroid Moment Tensor (Global CMT) Project, we test the general orthogonal regression (GOR) and the ordinary least-squares (OLS) methods in M w – M L , M s , and m b conversions for earthquakes in three different tectonic structures of western China. For M L and m b , linear trends vary according to tectonic structures, which implies different body-wave attenuations in the three structures. For M s , the results are similar, whether using the GOR or the OLS method, but slopes of regression lines are not close to 1, which indicates routine misestimates of M s in western China. The GOR slopes are uniformly larger than the OLS slopes in all magnitude conversions. Standard deviations are between 0.06 and 0.13 for the GOR method but are between 0.12 and 0.25 for the OLS. Thus, the GOR is found to be superior to the OLS method and its use is recommended. Conversions of different magnitudes to M w not only imply different patterns of seismic-wave attenuations but will also benefit immediate assessment of seismic damage after occurrence of a destructive earthquake in the future. Online Material: Earthquake catalog and tables showing differences between magnitude estimates for M w , M L , m b , and M s .
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    The Complex Velocity Variation Induced by the Precipitation and the 2018 Eruption of the Kilauea Volcano in Hawaii Revealed by Ambient Noise (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉In this study, we used a new method called the peak‐trough phase shift (PTPS) method to obtain velocity change from the direct surface wave. A graphic user interface was developed to facilitate manual quality control and visualize the results instantly for quality assessment. Comparing the results measured by the stretching method, the PTPS method is proved to be reliable. We applied this method in the Kilauea volcano region and found that the velocity change of the sediment layer is complicated by the joint influences of the precipitation and the eruption. Precipitation‐velocity changes scatter diagrams can help us to quantitatively separate the influences of two factors. The two major contributing factors included the water saturation of microcracks and the filling of magma in large fractures. Significantly, our results revealed two phases of magma activities before the 2018 eruption: (1) in the first phase, the upward migration of the magma increased the compressional stresses and closed the large connected fractures and microcracks and therefore increased velocity, and (2) in the second phase, the magma injected into large veins and fractures, which resulted in sharply decreased velocity.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 3
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    Anomalous Pn Amplitudes through the Southeastern Tarim Basin and Western Tien Shan along Two Profiles: Observations and Interpretations (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-03-23
    Description: We observe substantial amplitude anomalies of Pn waveforms that propagated through the southeastern Tarim basin and western Tien Shan along the two profiles, which are from an earthquake that occurred on the southeastern margin of Tarim basin. Although there is only a 5° difference in azimuth from the epicenter for the two profiles, the Pn amplitude differences along them are significant. The synthetic seismograms in the band of 0.5–1.5 Hz for different models along the two profiles are simulated to interpret the observed anomalies. The simulation results indicate that the Pn anomalies along the two profiles may not result from the earthquake focal mechanism or the average-layered mantle lid structure. The Moho topography along the R–A profile may mainly account for the drastic variation of Pn amplitudes in 0.5–1.5 Hz as the epicentral distance increases from 850 to 1100 km, whereas the Moho topography and the velocity heterogeneity may together account for the observed Pn anomalies in the band of 0.5–1.5 Hz along the R–B profile.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 4
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    The Complex Velocity Variation Induced by the Precipitation and the 2018 Eruption of the Kilauea Volcano in Hawaii Revealed by Ambient Noise (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉In this study, we used a new method called the peak‐trough phase shift (PTPS) method to obtain velocity change from the direct surface wave. A graphic user interface was developed to facilitate manual quality control and visualize the results instantly for quality assessment. Comparing the results measured by the stretching method, the PTPS method is proved to be reliable. We applied this method in the Kilauea volcano region and found that the velocity change of the sediment layer is complicated by the joint influences of the precipitation and the eruption. Precipitation‐velocity changes scatter diagrams can help us to quantitatively separate the influences of two factors. The two major contributing factors included the water saturation of microcracks and the filling of magma in large fractures. Significantly, our results revealed two phases of magma activities before the 2018 eruption: (1) in the first phase, the upward migration of the magma increased the compressional stresses and closed the large connected fractures and microcracks and therefore increased velocity, and (2) in the second phase, the magma injected into large veins and fractures, which resulted in sharply decreased velocity.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 5
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    Testing the Depths to 1.0 and 2.5    km / s Velocity Isosurfaces in a Velocity Model for Japan and Implications for Ground‐Motion Modeling (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉In the Next Generation Attenuation West2 (NGA‐West2) project, a 3D subsurface structure model (Japan Seismic Hazard Information Station [J‐SHIS]) was queried to establish depths to 1.0 and 2.5  km/s velocity isosurfaces for sites without depth measurement in Japan. In this article, we evaluate the depth parameters in the J‐SHIS velocity model by comparing them with their corresponding site‐specific depth measurements derived from selected KiK‐net velocity profiles. The comparison indicates that the J‐SHIS model underestimates site depths at shallow sites and overestimates depths at deep sites. Similar issues were also identified in the southern California basin model. Our results also show that these underestimations and overestimations have a potentially significant impact on ground‐motion prediction using NGA‐West2 ground‐motion models (GMMs). Site resonant period may be considered as an alternative to depth parameter in the site term of a GMM.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    Testing the Depths to 1.0 and 2.5    km / s Velocity Isosurfaces in a Velocity Model for Japan and Implications for Ground‐Motion Modeling (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉In the Next Generation Attenuation West2 (NGA‐West2) project, a 3D subsurface structure model (Japan Seismic Hazard Information Station [J‐SHIS]) was queried to establish depths to 1.0 and 2.5  km/s velocity isosurfaces for sites without depth measurement in Japan. In this article, we evaluate the depth parameters in the J‐SHIS velocity model by comparing them with their corresponding site‐specific depth measurements derived from selected KiK‐net velocity profiles. The comparison indicates that the J‐SHIS model underestimates site depths at shallow sites and overestimates depths at deep sites. Similar issues were also identified in the southern California basin model. Our results also show that these underestimations and overestimations have a potentially significant impact on ground‐motion prediction using NGA‐West2 ground‐motion models (GMMs). Site resonant period may be considered as an alternative to depth parameter in the site term of a GMM.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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