Dynamic Triggering of Earthquakes and Tremors in Taiwan

Abstract:

Distant earthquake matters. Its long period, long lasted surface waves could bring transient stresses, later the local stress state, and trigger earthquakes and tremors at remote distances. There exists mounting evidences for the role of dynamic stress in slow/fast earthquakes triggering. Yet, little is understood about the similar/different processes for triggered earthquakes and tremors. What is the response of tremors and earthquakes to a remote earthquake? Are the triggered tremor and earthquakes co-located? Are the triggering controlled by the characteristics of distant earthquakeor local physical condition? With generation potential of non-volcanic tremors and frequent earthquake activity, Taiwan serves as a natural laboratory to explore the similarity and difference in triggering response of tremor and earthquakes. Using a collection of Mw ≥ 7.0 events from Sumatra constraint by similar azimuth, we seek to understand the general characteristics of tremors and earthquakes triggered by Sumatra events, furthermore, discuss the predominant factors of triggering in Taiwan.

By examining all recordings of the 24 Sumatra Mw ≥ 7.0 earthquakes from 2000 to 2014 , we identified four triggered tremors and 12 triggered earthquakes that occurred during the surface wave passage. The Sumatra earthquakes that triggered tremors are characterized by thrust-type focal mechanisms with right-lateral component and minimum dynamic stress of ~3 kPa. The minimum dynamic stress measured for triggered earthquakes, however, is ~0.4 kPa, smaller than that of triggered tremor. The different location and stress triggering threshold for triggered tremors and earthquakes indicates different triggering mechanisms. Triggered tremors are confined in southern Central Range characterized by high attenuation, high thermal anomaly, the boundary between high and low resistivity, and localized veins on the surfaces distributed, suggesting the involvement of fluids from metamorphic dehydration within the orogen. The good correlation between the location of triggered earthquakes and geothermal anomalies on the other hand, indicates that the regimes hosting geothermal activity are more susceptible to remote earthquake triggering.