Global Search of Deep Triggered Non-Volcanic Tremor

Speaker: Kevin Chao
Deep “non-volcanic” tremor has been observed at many major plate-boundary faults. Recent studies have shown that triggered tremor occurs on the same fault patches as ambient tremor and can be used as a proxy to estimate background tremor activity. A systematic global search of triggered tremor could help to identify the physical mechanisms and necessary conditions for tremor generation. Following our previous studies, we conduct a global search for tremor triggered by teleseismic earthquakes on major subduction zones around the Pacific Rim. These include the Nankai subduction zone and Kyushu, Honshu, and Hokkaido regions in Japan, New Zealand, the Cascadia subduction zone, Alaska and Aleutian Arc, and the major subduction zones in Central and South America. In addition, we examine major strike-slip faults around the Caribbean plate, the Alpine fault in the South Island of New Zealand, the Queen Charlotte fault in northern Pacific Northwest Coast, and the San Andreas fault system in California, and the collision environment in Taiwan. In each place, we first identify triggered tremor as a high-frequency non-impulsive signal that is in phase with the large-amplitude teleseismic waves. When possible, we locate triggered tremor using a standard envelope cross-correlation technique. We also calculate the dynamic stress and check the triggering relationship with the Love and Rayleigh waves. Finally, we calculate the triggering potential with the local fault orientation and surface-wave incident angles. Our current results suggest that tremor could be triggered at many plate-boundary faults in different tectonic environments. Their triggering behavior could be best explained under the Coulomb-Griffith failure criteria. The apparent triggering threshold is on the order of 1-10 KPa, although this value could be partially influenced by the background noise level or quality and quantity of seismic data.