Abstract
Systematic determination of reliable source parameters for regional earthquakes in Taiwan, particularly offshore events with m(subscript b)＜5.5, has been a difficult task because of poor coverage by the local network and the lack of signals at teleseismic distances. Establishment of the ”Broadband Array in Taiwan for Seismology (BATS)” has greatly improved such a task through moment-tensor inversion of regional waveforms. Our inversion algorithm differs from previous studies in two major aspects. First, we evaluate the characteristics of background noise for individual stations. The results are then used to determine the lower corner of the frequency band used in the inversion to maximize the long-period information in waveforms. The higher corner is set at 0.06-0.08 Hz to avoid the effects of strong lateral heterogeneity and possible epicentral mislocation. Second, to further reduce the uncertainty caused by complex structures, a two-step procedure is adapted to select the best velocity models for different stations in calculating the synthetics. The inversion quality is classified by a combination of a letter (A-F) and a digit (1-4) reflecting the waveform misfit and the compensated linear vector dipole (CLVD) component, respectively. In total, source parameters of 36 events that occurred between July 1995 and December 1996 are reported in this study. For the few events that are big enough to be studied teleseismically, most of our solutions are consistent with those reported by other institutions. We intend to make our inversion results available on a routine basis that they will not only be able to provide precise source parameters for smaller regional earthquakes, but will also serve as an alternative to independently examine solutions of large and moderate-sized events reported from other sources.
Highlights
Precise determination of seismic source parameters is a fundamental issue in earthquake 1 1nstitute of EarthSciences, AcademiaSinica, Taipei, Taiwan, AOCTAO, Vol 10, No 3, September 1999 studies
We report source parameters only if they meet the following criteria: (1) 3component waveforms from at least three stations are used in the inversion, and (2) the quality of inversion must be higher than C4
The choice of a different frequency band and velocity model depends on each station's background noise level and structural setting, re spectively, making the inversion less sensitive to the island's high background noise and com plex velocity heterogeneity
Summary
Precise determination of seismic source parameters is a fundamental issue in earthquake 1 1nstitute of EarthSciences, AcademiaSinica, Taipei, Taiwan, AOCTAO, Vol 10, No 3, September 1999 studies. Precise determination of seismic source parameters is a fundamental issue in earthquake 1 1nstitute of Earth. Since the early 80's, both the development of centroid-moment-tensor (CMT) inver sion technique and increasing coverage of global digital seismic networks have led to the success of systematic determination of earthquake source parameters in large quantity (e.g., Dziewonski et al, 1981; Kawakatsu et al, 1995; Sipkin, 1982). Point source CMT inversion has become routine practice for regional earthquakes occurring in the western U.S (e.g., Zhu and Helmberger, 1996; Pasysnos et al, 1996). In mid-1992, the Institute of Earth Sciences (IES), Academia Sinica, along with several domestic and foreign institutions, began to prepare a prospectus for establishing a broadband seismic network in the Taiwan region.
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