Earthquake Source Scaling of Moderate to Large Earthquakes in Taiwan: Study of 2003 Mw >6 Taiwan Earthquakes

We inverted velocity data from Broadband Array in Taiwan for Seismology (BATS) to study earthquake source parameters of three Mw>6 earthquakes in eastern Taiwan. These earthquakes occurred on June 9th, June 10th and Dec 10th, 2003, respectively. We use the least-square method to invert for the distribution of slip and other source parameters. The slip distribution and aftershock data were used to estimate the fault geometry. For each event, we derived a preferred model by testing different focal mechanisms. In order to have better azimuthal coverage to the earthquake, one Japanese station, YNG, from F-net was also used. Our results show that these earthquakes all have thrust fault mechanisms. The hypocenter of the June 9th earthquake is 24.4° N, 121.99° E, and has a depth of 21.3 km. The focal mechanism has a strike, dip, and rake of 225° , 26° , and 121° , respectively. The moment is 8.65×1024 dyne-cm, which yields the Mw of 5.89. The main rupture is around the hypocenter, and propagates towards the northeast. The June 10th earthquake occurred at 23.52° N, 121.67° E, at a depth of 32.3 km. The focal mechanism has a strike, dip, and rake of 217° , 39 ° , and 110° , respectively. The moment is 2.03×1025 dyne-cm, which yields the Mw of 6.13. It ruptured toward the northeast. The September 10th earthquake occurred at 23.07° N, 121.40° E at a focal depth of 17.7 km. The focal mechanism has a strike, dip, and rake of 3° , 42° , and 104° , respectively. The moment is 2.68×1025 dyne-cm, which yields the Mw of 6.22, with the main slip concentration to the north. According to the slip and aftershock distributions, this earthquake is believed to be associated with the Chihshang fault. We have investigated the relationship of earthquake magnitude (Mw) to fault length (L₂), fault area (A₂) and average slip (D₂). The relations among the source parameters are as follows: Mw = 1.4log(L₂)+4.5, Mw = 0.8log(A₂)+4.5, Mw = (1.3±0.45)log(D₂)+3.7 These scaling relationships provided important information for seismic hazard analysis and for better understanding of earthquake source characteristics in Taiwan.