Temporal changes of seismic velocity associated with the 2006 Mw 6.1 Taitung earthquake in an arc-continent collision suture zone

To detect temporal changes of elastic properties associated with the 2006 Mw 6.1 Taitung earthquake in southeast Taiwan, whereby the collision between the Luzon arc riding on the Philippine Sea plate and the Asian margin is taking place, we construct the Green's functions from auto-and cross-correlation function (ACF and CCF) of continuous ambient noise between stations. Time lapse changes in the retrieved coda arrivals are estimated for monitoring spatiotemporal variations of seismic velocities around the ruptured fault zones. To the south of the main shock epicenter where the earthquake may have ruptured along two perpendicularly-intersecting fault planes resulting in intense coseismic slip and widely-dispersed aftershocks, the ACFs (2-8Hz) at nearby stations reveal a large, sudden velocity drop of over 1% after the event occurrence. The CCFs (0.1-0.9Hz) also show moderate reduction about 0.1% for the interstation paths traveling through the southeast quadrant of the focal sphere which has experienced the maximum peak ground acceleration and dilatational strain change. The intense seismic shaking combined with the rupture-induced damage near the junction of the two faults is the most plausible cause for such localized, but significant coseismic velocity reduction. The response of groundwater levels to precipitation is in-phase correlated with velocity variations over 3years of investigation. Unlike the postseismic surface displacements gradually relaxed, the velocity remained slow until October 2006 due to the typhoon-induced heavy rains between May and September. © 2012. American Geophysical Union. All Rights Reserved.