Earth Planets Space, Vol. 57 (No. 10), pp. 987-994, 2005
G. M. Besana1,2,3 and M. Ando1
1Research Center for Seismology, Volcanology, and Disaster Mitigation, Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
2Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, Quezon City, Philippines 1110
3National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City, Philippines 1110
(Received November 29, 2004; Revised July 18, 2005; Accepted August 7, 2005)
The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zone with slow slip and creep activity. This is based on the analysis and correlation of seismic historic data and detailed documentation of recent seismic events in the region. Based on this study the Guinyangan fault is defined to be the northern locked portion with recurrence interval of as short as 65 years. The Masbate fault is the central part with large and medium earthquakes accompanied by unusually large ground rupture. The north Central Leyte fault and the south Central Leyte fault, on the other hand, are characterized by aseismic creep and medium-sized events, usually with clusters of foreshocks, respectively. Unusual seismic activity both on the Masbate fault and Central Leyte fault somehow correlates well with the behavior of known slow events and creep activity. Further investigation of this region could lead to deeper understanding of impending major earthquakes, especially along the Guinyangan fault, which usually produces larger damaging events, and for further understanding of the impact of slow events and creep on the adjoining active structures.
Key words: Philippine Fault Zone (PFZ), historical earthquakes, slow events, creep, Masbate fault, transition zone, Guinyangan fault, Leyte fault.