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TitleThe significance of tomographic edge zones for large earthquakes in Taiwan
AuthorWang, Z; Kao, HORCID logo
SourceJournal of Geophysical Research, Solid Earth vol. 124, issue 11, 2019 p. 11822-11839, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190260
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf; html
AreaTaiwan, Province of China
Lat/Long WENS 120.0000 122.0000 25.0000 22.0000
Subjectsgeophysics; tectonics; Science and Technology; Nature and Environment; Health and Safety; seismology; earthquakes; earthquake magnitudes; earthquake risk; seismic risk; earthquake catalogues; geophysical surveys; seismic surveys; seismic velocities; anomalies; tectonic setting; subduction zones; fluid migration; pore pressures; compaction; models; bedrock geology; basement geology; structural features; faults; correlations; 1999 M7.6 Chi-Chi Earthquake; 2016 M6.5 Meinung Earthquake; 2018 M6.4 Hualien Earthquake; Philippine Sea Plate; Luzon Arc; mitigation; Mitigation; Phanerozoic; Cenozoic; Quaternary; Tertiary
Illustrationslocation maps; geoscientific sketch maps; plots; profiles; models; histograms; cross-sections; bar graphs; time series; tables
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2019 11 29
AbstractSeismogenesis of large earthquakes in Taiwan are often controlled by regional tectonics. Despite decades of efforts, the detailed relationship between seismogenesis of disastrous earthquakes and the geophysical properties of the earth materials remains unclear. In this study, we conduct high?resolution tomography inversion of seismic velocities (Vp and Vs) and the Poisson's ratio (sigma), and the results are used to infer the three?dimensional (3-D) distributions of crack density (epsilon) and saturation rate (zeta). We find that more than 70% of large (moment or local magnitudes greater than or equal to 6, M6+) earthquakes occurred along tomographic edge zones (TEZ) within the crust where the spatial gradient exceeds 0.1, including all three disastrous events in the past two decades: the 1999 M7.6 Chi-Chi, 2016 M6.5 Meinung, and the 2018 M6.4 Hualien earthquakes. We attribute the preference of large crustal earthquakes along TEZ as the consequence of fluid migration from the more saturated side to the opposite, leading to the build-up of high pore pressure along TEZ. Locations of historical M6+ earthquakes are consistent with the inference of excessive fluids from either the extensive dehydration of hydrous minerals within the subducting Philippine Sea plate or the sedimentary compaction of alluvium and clastic deposits in the foreland basin west of the orogenic belt. Positive correlation between M6+ earthquakes and TEZ is not unique to Taiwan. Several famous earthquakes in regions with different tectonic settings appear to be associated with local TEZ. Our study could provide insights to long-term mitigation of regional seismic hazards in Taiwan and probably elsewhere.
Summary(Plain Language Summary, not published)
Seismic activities in Taiwan are related to regional tectonic processes. Here, we conduct high-resolution inversion to image the distributions of seismic velocities, Poisson's ratio, crack density, and saturation rate in Taiwan. We find that all large disastrous earthquakes that occurred during the past 2 decades in Taiwan occurred along the boundary zones between high and low tomographic anomalies. Based on both local and global earthquake catalogues, we find that the tomographic edge zones (TEZ) account for more than 70% of large (M>/=6) earthquakes in Taiwan during the past century. Furthermore, the positive correlation between TEZ and large crustal earthquakes can be established for several other regions with different tectonic settings where high-resolution tomography is available. Our model provides important insights into the likely locations of future large earthquakes in Taiwan and probably elsewhere, which may have significant implications to the long-term mitigation of regional seismic hazards.

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