Development and Operation of a Regional Moment Tensor Analysis System in the Philippines: Contributions to the Understanding of Recent Damaging Earthquakes
Baby Jane T. Punongbayan*1, Hiroyuki Kumagai*2,
Nelson Pulido*3, Jun D. Bonita*1, Masaru Nakano*4,
Tadashi Yamashina*5, Yuta Maeda*2, Hiroshi Inoue*3,
Arnaldo A. Melosantos*1, Melquiades F. Figueroa*1,
Ponczh Colleen M. Alcones*1, Karl Vincent C. Soriano*1,
Ishmael C. Narag*1, and Renato U. Solidum, Jr.*1
*1Philippine Institute of Volcanology and Seismology (PHIVOLCS), PHIVOLCS Building, C.P. Garcia Ave, Univ. of the Philippines, Diliman, Quezon City 1101, Philippines
*2Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
*3National Research Institute for Earth Science and Disaster Prevention (NIED), Ibaraki, Japan
*4R&D Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
*5Kochi Earthquake Observatory, Faculty of Science, Kochi University, Kochi, Japan
A network of 10 satellite-telemetered broadband stations was established under a cooperative project between Japan and the Philippines, and a source analysis system based on waveform inversion of regional seismograms was adapted to operationalize a regional moment tensor analysis of Philippine earthquakes. This study presents the source information generated by the system for recent damaging earthquakes: the Mw6.7 Negros and Mw7.6 offshore Samar in 2012, and the Mw7.2 in Bohol in 2013. Results show that the Negros event was generated by shallow NE–SW thrust faulting with a small strike-slip component, and that the centroid was located slightly offshore. The Samar event occurred in relation to an outer-trench thrust fault within the Philippine Sea Plate, adjacent to a part of the Philippine Trench that has relatively low seismicity. Our centroid moment tensor (CMT) solutions show that the Samar event triggered distinct clusters of outer-rise normal and thrust aftershocks, which we explain as being consistent with a Coulomb stress change in the area. Finally, we infer that the previously unidentified fault zone that generated the Bohol earthquake has a length of ∼ 100 km, is oriented ENE–WSW, transects parts of Bohol, and extends offshore towards Cebu. These examples show how recent improvements in Philippine earthquake monitoring could contribute to the characterization of earthquake sources and in the understanding of the seismotectonics of the area.
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