Source Characterization of the 15 November 1994, Ms 7.1 Mindoro, Philippines Earthquake

The 14 November 1994, Mindoro, Philippines earthquake (Ms = 7.1) was a major right lateral strike slip event associated to the movement along zones of weakness transecting the Philippine archipelago along the Aglubang River Fault. We examined this event in order to characterize its tectonic origin using the inversion of teleseismic body waveform data and the method developed by Kikuchi and Kanamori (1990). The earthquake was particularly devastating, generating tsunami that has killed 78 persons, and considered as one of the major events since 1992 around the Pacific Rim. The origin of the tsunami has remained an enigma to date in the scientific community. The digitally recorded broadband teleseismic data was downloaded from the archives of IRIS-DMC and was deconvolved to check the direction of P wave initial motion. Retrieved polarity data was then utilized for the estimation of the fault plane solution using the program FOCMEC_@(Snoke). The result suggests an almost purely strike slip faulting in the NE-SW trending direction which correlates well with the mapped trace of ground rupture. The observed waveforms were complicated and show some aspect of multiple shocks. The focal mechanism solutions from the preliminary inversion of teleseismic body waveforms reveal that the event was dominated by major shear faulting, however, the dislocation source based on the parent earthquake failed to model exceptional run-up amplitude. We performed a careful inspection of the body waveforms for multiple event analysis in search for its spatio-temporal distribution. The result suggests that the 1994 Mindoro earthquake consists of two sub-events and that these events are separated by 9 seconds and are located about 30 km apart from each other. We also infer from the inspection that some later pulses observed in the waveforms could be related to depth phase rather than complexity of the source. Effect of wave propagation in the source region was tested by searching the existence of similar observations in the waveforms convolved for the main shock using a smaller event that has occurred in the vicinity of the source region under study. Finally, we again performed the inversion of all the available teleseismic body waveforms, using the information gathered from the above analysis. We separately analyzed the azimuthal amplitude and phase variations of long-period surface waves for determining the radiation pattern that constrain the source characterization at long periods.