Synchronized and asynchronous modulation of seismicity by hydrological loading: A case study in Taiwan

Ya-Ju Hsu; Honn Kao; Roland Bürgmann; Ya-Ting Lee; Hsin-Hua Huang; Yu-Fang Hsu; Yih-Min Wu; Jiancang Zhuang

doi:10.1126/sciadv.abf7282

Synchronized and asynchronous modulation of seismicity by hydrological loading: A case study in Taiwan

Sci Adv. 2021 Apr 14;7(16):eabf7282. doi: 10.1126/sciadv.abf7282. Print 2021 Apr.

Authors

Ya-Ju Hsu^{1

2}, Honn Kao³, Roland Bürgmann⁴, Ya-Ting Lee⁵, Hsin-Hua Huang⁶, Yu-Fang Hsu², Yih-Min Wu^{2

7}, Jiancang Zhuang^{8

9}

Affiliations

¹ Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan. yaru@earth.sinica.edu.tw.
² Department of Geosciences, National Taiwan University, Taipei, Taiwan.
³ Pacific Geoscience Centre, Geological Survey of Canada, Nature Resources Canada, Sidney, BC, Canada.
⁴ Berkeley Seismological Laboratory, University of California, Berkeley, CA, USA.
⁵ Department of Earth Sciences, National Central University, Taoyuan, Taiwan.
⁶ Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan.
⁷ Research Center for Future Earth, National Taiwan University, Taipei, Taiwan.
⁸ Institute of Statistical Mathematics, Research Organization of Information and Systems, Tokyo, Japan.
⁹ Department of Statistical Science, The Graduate University for Advanced Studies, Tokyo, Japan.

Abstract

Delineation of physical factors that contribute to earthquake triggering is a challenging issue in seismology. We analyze hydrological modulation of seismicity in Taiwan using groundwater level data and GNSS time series. In western Taiwan, the seismicity rate reaches peak levels in February to April and drops to its lowest values in July to September, exhibiting a direct correlation with annual water unloading. The elastic hydrological load cycle may be the primary driving mechanism for the observed synchronized modulation of earthquakes, as also evidenced by deep earthquakes in eastern Taiwan. However, shallow earthquakes in eastern Taiwan (<18 km) are anticorrelated with water unloading, which is not well explained by either hydrological loading, fluid transport, or pore pressure changes and suggests other time-dependent processes. The moderate correlation between stacked monthly trends of large historic earthquakes and present-day seismicity implies a modestly higher seismic hazard during the time of low annual hydrological loading.

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