Temporal variation of tectonic tremor activity in southern Taiwan around the 2010 ML6.4 Jiashian Earthquake

Deep tectonic tremor, which is extremely sensitive to small stress variations, could be used to
monitor fault-zone processes during large earthquake cycles and aseismic processes before
large earthquakes. In this study, we develop an algorithm for the automatic detection and
location of tectonic tremor beneath the southern Central Range of Taiwan and examine the
spatio-temporal relationship between tremor and the 4 March 2010 ML6.4 Jiashian
earthquake, located about 20 km from active tremor sources. We find that tremor in this
region has a relatively short duration, short recurrence time, and no consistent correlation
with surface GPS data. We find a short-term increase in the tremor rate 19 days before the
Jiashian mainshock, and around the time when the tremor rate began to rise, one GPS station
recorded a flip in its direction of motion. We hypothesize that tremor is driven by a slow-slip
event that preceded the occurrence of the shallower Jiashian mainshock, even though the
inferred slip is too small to be observed by all GPS stations. Our study shows that tectonic
tremor may reflect stress variation during the pre-nucleation process of a nearby earthquake.