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

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.

Investigating the Impacts of a Wet Typhoon on Microseismicity: A Case Study of the 2009 Typhoon Morakot in Taiwan Based on a Template Matching Catalog

“…In a typical mainshock-aftershocks cluster, aftershocks are triggered by the mainshock, and hence are not considered as independent events. To avoid over-counting these clustered/dependent events, we decluster the MFT catalog, similar to the recent studies in Taiwan (Hsu et al, 2021;Steer et al, 2020). Specifically, we calculate the probability of background seismicity for each event above Mc in the MFT catalog using a stochastic declustering method (Zhuang, 2006;Zhuang et al, 2002Zhuang et al, , 2004 based on the epidemic-type aftershock sequence (ETAS) model (Table S3 in Supporting Information S1) (Ogata, 1988).…”

“…Steer et al (2020) attributed this to the crustal unloading caused by the intense and prolonged sediment erosion after typhoon Morakot in the landslide zone. Hsu et al (2021) pointed out that another possible mechanism related to the interannual variation of terrestrial water storage, rather than the typhoon-associated landslides and erosions.…”

“…3. Seismicity changes can be triggered by transient events such as another earthquake at nearby or teleseismic distances (Freed, 2005;Hill & Prejean, 2015), by both short-term (e.g., typhoons or hurricanes (X. F. Meng et al, 2018)) and long-term (e.g., annual and internal hydrological loading/unloading (Hsu et al, 2021) processes, in addition to regular tectonic loading. Hence, it is important to separate the effects from long-term changes on seismicity rate changes first, before analyzing any short-term effects due to extreme weather events.…”

“…They concluded that these changes were induced by landslides and subsequent erosion driven by typhoon Morakot and lasted for at least 2.5 years. In another recent study, Hsu et al (2021) found seasonal seismicity rate variations in western Taiwan. They proposed that these variations are driven by interannual hydrological changes in that region.…”

Brief communication: Seismological analysis of flood dynamics and hydrologically-triggered earthquake swarms associated with storm Alex

“…Over the past two decades, a growing number of studies has shown a correlation between meteorological events and earthquake activity in various geological contexts (Costain and Bollinger, 2010). Several sites show the seasonal modulation of the seismicity due to rainfall or snowmelt periods in Japan (Ueda and Kato, 2019); Nepal (Kundu et al, 2017); Taiwan (Hsu et al, 2021); Oregon, USA (Saar and Manga, 2003); California, USA (Johnson et al, 2017;Montgomery-Brown et al, 2019); and Italy (D'Agostino et al, 2018). Other observations display a punctual increase of seismic activity following an exceptional rainfall episode, for example in the Swiss Alps (Roth et al, 1992), German Alps (Kraft et al, 2006), and southern France (Rigo et al, 2008).…”