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Spatio-Temporal Changes of Microseismicity in Taiwan Around the 2009 Typhoon Morakot

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology I

Type: Oral

Date: 4/21/2021

Presentation Time: 02:30 PM Pacific

Description: 

Typhoon Morakot brought up to 3 meters of rainfall within a few days in August 2009, leading to numerous landslides in Southern Taiwan. The subsequent erosional processes result in a reduction of normal load at depth. Previous studies have suggested that such transient stress change can trigger small to moderate-size earthquakes in Taiwan and elsewhere. In this study, we examine spatio-temporal changes of microseismicity in Taiwan around the 2009 Typhoon Morakot to better understand the possible triggering relationship between extreme weather events, landslides and sediment removal, and tectonic activities. Because many microearthquakes were missing from the standard earthquake catalogs (especially during and right after Typhoon Morakot), we apply the Matched Filter Technique to systematically detect microearthquakes in Taiwan half a year before to one year after Typhoon Morakot. We use 71 short-period stations in the Central Weather Bureau (CWB) and 31508 CWB catalog events around Taiwan as the templates to scan through the continuous seismic data. We detect about 7 times as many events as in the standard CWB catalog. After relocation with the double-difference technique, there are about 3 times as many events as in the standard CWB catalog. In addition, we train a deep learning model to measure the P-wave first motion polarities for events in our newly built catalog. Based on these polarities, we calculate the focal mechanisms for about 2500 events. We observe a transient decrease of microseismicity during and in the following few weeks following Typhoon Morakot, likely due to high noise levels and station outage caused by the typhoon and associated rainfalls/landslides. We find a possible seismicity rate decrease of the normal-fault events after Morakot in the heavy–rainfall region. However, such changes are not clear for strike-slip and thrust-fault events. In summary, Our results do not show a clear change in microseismicity before/after Typhoon Morakot in the analyzed time period.

Presenting Author: Qiushi Zhai

Student Presenter: Yes

Authors