Remote triggering of non-volcanic tremor around Taiwan

Abstract

S U M M A R YWe perform a systematic survey of triggered deep 'non-volcanic' tremor beneath the Central Range (CR) in Taiwan for 45 teleseismic earthquakes from 1998 to 2009 with M w ≥ 7.5 and epicentral distance ≥1000 km to the broad-band station TPUB. Triggered tremors are visually identified as bursts of high-frequency (2-8 Hz), non-impulsive and long-duration seismic energy that are coherent among many seismic stations and modulated by the teleseismic surface waves. Out of the 45 earthquakes, we identified nine teleseismic events associated with nine tremor sources in the southern and five in the northern CR. Most of the tremor sources are located within the depth range of 15-25 km in the lower crust above the Moho. We find that the amplitudes of the surface waves play an important role in determining the triggering potential, and the apparent triggering threshold is ∼0.1 cm s −1 , or 7-8 KPa. However, such threshold is partially controlled by the background noise level, which could prevent weaker tremor triggered by surface waves with smaller amplitudes from being identified. The amplitudes of the triggered tremor show a positive correlation with the amplitudes of the triggering surface waves, consistent with the predictions by the 'clock-advance' model. In addition to amplitudes, other factors, such as frequency contents and incidence angles, also affect the triggering potential. We find that intermediate-period (30-10 s) surface waves could trigger/modulate tremors, suggesting that long-period (>30 s) surface waves are not always required in long-range triggering. Tremors appear to be triggered by both Love and Rayleigh waves. When the incidence angles are parallel to the strike of the CR, all six events triggered tremor primarily during the Rayleigh waves. For strike normal incidence, only the 2001 M w 7.8 Kunlun earthquake showed predominant Love-wave triggering. This observation can be qualitatively explained by a simple Coulomb failure for a left-lateral shear on the low-angle detachment fault beneath the southern CR.

Detecting Deep Tectonic Tremor in Taiwan with a Dense Array

“…This is consistent with similar findings in Cascadia (Ghosh et al, 2009(Ghosh et al, , 2010(Ghosh et al, , 2012, suggesting that array techniques have higher detection capabilities than traditional WECC techniques (Wech and Creager, 2008). Unfortunately, we did not have an existing fault interface model in this region (Chao et al, 2012), so we were unable to project the best slowness of tremor detection back to the source region to determine the tremor location, as was done in Cascadia and other regions (e.g., Ghosh et al, 2009).…”

“…In the arc-continent collision environment in Taiwan, tremor is found mainly beneath the southern Central Range (Peng and Chao, 2008;Tang et al, 2010Tang et al, , 2013Chao et al, 2011Chao et al, , 2012Chao et al, , 2013Chuang et al, 2014;Idehara et al, 2014).…”

“…Peng and Chao (2008) first identified triggered tremor beneath the Central Range following the 2001 M w 7.9 Kunlun earthquake in northern Tibet. Subsequent tremor studies mainly focus on low-frequency earthquakes (Tang et al, 2010(Tang et al, , 2013 and both triggered (Chao et al, 2012 and ambient tremor (Chao et al, 2011;Chuang et al, 2014;Idehara et al, 2014) in the southern Central Range. Those studies utilized seismic data from two permanent seismic networks-the Broadband Array in Taiwan for Seismology (BATS) operated by the Institute of Earth Sciences in Academia Sinica (Kao et al, 1998) and the short-period Central Weather Bureau Seismic Network (CWBSN) and the Broadband Seismic Network is marked as the solid star.…”

A Global Search for Triggered Tremor Following the 2011 Mw 9.0 Tohoku Earthquake

“…Gomberg (2010) further examined the relationship between the amplitudes of the triggering waves and triggered tremor from four observations in Cascadia (Rubinstein et al, 2009) and found that the results did not match the predictions of the clock-advance model. Chao, Peng, Wu, et al (2012) found a positive relationship between the amplitudes of surface waves from nine teleseismic earthquakes and those of triggered tremor beneath the Central Range in Taiwan. In addition, Chao, Peng, Fabian, et al (2012) compared triggered tremor observed in the Parkfield-Cholame section of the SAF with the San Jacinto fault (SJF) in southern California and the Calaveras fault (CF) in northern California.…”

“…The analysis procedure generally follows that of previous studies (Peng et al, 2009;Chao, Peng, Wu, et al, 2012) and is briefly described here. We download three-component broadband and short-period seismograms in each region (see Data and Resources), select the data from 1000 s before and 9000 s after the origin time of the Tohoku mainshock, remove the mean of the signals, and generate either band-pass (2-8 Hz) or high-pass (> 5 Hz) filtered seismograms.…”