Temporal b-Value Variations throughout a Seismic Faulting Process: The 2008 Taoyuan Earthquake in Taiwan

Temporal b-value variations have been completely obtained for the seismic faulting process of the 4 March 2008 Taoyuan earthquake (M-L = 5.2), southern Taiwan. In addition to triggering several hundred aftershocks, the mainshock was preceded by two groups of foreshocks (64 events) that clustered along the narrow major fault zone. A high b-value of similar to 1.25, estimated from the foreshock series, representing fault growth, was significantly larger than the b-values of 0.80 and 0.81, obtained respectively from aftershocks and background seismicity. Also there were some pre-shocks (i.e., micro-earthquakes) that occurred one month before the earthquake sequence, with an extremely high b-value of similar to 2.1. This number might successfully indicate pre-nucleation seismic features in the vicinity of the fault zone. These seismic characteristics are fundamentally very similar to general features such as fracture nucleation and growth observed in rock samples under controlled stress in laboratory experiments, and thus ought to be considered to improve our understanding of crustal fault growth.