Imaging the Internal Structure along the Longitudinal Valley Fault System, Taiwan, Using Fault Zone Head Waves
Abstract
Fault zone head waves provide high-resolution information on fault structure at seismogenic depths. Here we use head waves to examine the Longitudinal Valley fault (LVF) system in Eastern Taiwan, a 150-km-long suture zone between the Eurasian plate and the Philippine Sea plate. Many past catastrophic earthquakes highlight the need for an improved understanding of fault characteristics and mechanical properties in this tectonically active environment. We analyze earthquake waveforms recorded by 87 stations of three seismic networks in Taiwan. The used stations are located on both sides along the 70 km long northern segment of the LVF. We focus on ~13000 small-to-moderate earthquake seismograms recorded between 2012 to 2018. We apply a set of algorithms developed by Ross & Ben-Zion to automatically detect and pick direct P waves and S waves, as well as potential head waves generated by earthquakes. Conservative detection parameters adapted from previous studies performed in strike-slip environments yield a robustly detected set of head waves excited by events that are located within a thin volume along the west-dipping Central Range fault , which now suggests—for the first time—the existence of a consistent velocity contrast across that fault segment. We parameterize a dipping interface from the hypocenters and estimate different material properties on the two sides from the head wave data using analytical formulae. To explore the effects of variable source mechanisms on head wave generation, properties, and detection, and to inform the adjustment of algorithmic detection parameters in more complex faulting environments such as Eastern Taiwan, we compute a suite of synthetic seismograms containing head waves and body waves using Finite Difference calculations. The seismogram database is again screened for head waves, and the anticipated larger detection data are compared to the previous set and further evaluated using polarization analysis.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMS062.0006L
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY