Moment Tensor Inversions Using Waveforms from Taiwan Strong-Motion Instrumentation Program (TSMIP): A Case Study of 22 October 1999 Taiwan Earthquake Sequence

We inverted Taiwan strong motion waveforms for the source mechanisms of the 22 October 1999 earthquake sequence to investigate seismogenic structure of Meishan fault system in Taiwan. In 1906, an earthquake of magnitude 7.1 shocked the Meishan area, and inflicted severe damages. Similar event might cause even greater damages due to the modern dense population in this region. However, detailed seismogenic structures in this region are still under debate, particularly whether the fault system contains right-lateral or left-lateral strike-slip fault is still not clear. The 22 October 1999 earthquake sequence in this region was recorded by a very dense strong-motion network, thus provided an unprecedented opportunity to study regional seismogenic structures. Here we modeled the waveforms using a moment tensor inverse procedure developed by Douglas Dreger of the Berkeley Seismological Laboratory. We have tested different 1D velocity models and found Rau and Wu’s model performs well in deriving reliable moment tensor solutions. We have compared our results with available, but limited, moment tensor solutions derived from broadband seismic waveforms for this sequence and found that it is possible to derive reliable moment tensor solutions using strong motion waveforms, at least in this case. We found an NE-SW trending fault system, which are consistent with shallow structures imaged by published seismic profiles. The derived moment tensor catalog sheds lights on the seismogenic structures at depth in this region, which can be useful for seismic hazard studies.