HR: 0800h
AN: S41B-0990    [Abstracts]
TI: Seismicity and Stress Change Along the Central Philippine Fault Zone
AU: * Besana, G M
EM: gmbesana@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho Chikusa-ku, Nagoya, 464-0802 Japan
AU: * Besana, G M
EM: gmbesana@seis.nagoya-u.ac.jp
AF: PHIVOLCS-DOST, UP DIliman Compound, Quezon City, 1100 Philippines
AU: * Besana, G M
EM: gmbesana@seis.nagoya-u.ac.jp
AF: University of the Philippines, UP Diliman, Quezon City, 1100 Philippines
AU: Ando, M
EM: ando@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho Chikusa-ku, Nagoya, 464-0802 Japan
AU: Ikuta, R
EM: ryoya@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho Chikusa-ku, Nagoya, 464-0802 Japan
AU: Daligdig, J A
EM: jessie@phivolcs.dost.gov.ph
AF: PHIVOLCS-DOST, UP DIliman Compound, Quezon City, 1100 Philippines
AU: Panol, M D
EM: myla@phivolcs.dost.gov.ph
AF: PHIVOLCS-DOST, UP DIliman Compound, Quezon City, 1100 Philippines
AU: Ikeda, A
EM: ikeda@nendai.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho Chikusa-ku, Nagoya, 464-0802 Japan
AU: Nakamura, T
EM: nakamura@nendai.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho Chikusa-ku, Nagoya, 464-0802 Japan
AB: Recent findings showed that the Philippine fault zone (PFZ) has a creeping section, a transition zone and a locked portion in its central portion. This part of the PFZ is comprised of the Guinyangan, Masbate, northern Leyte and southern Leyte faults. In this study, an attempt is taken to have a closer look on the seismic pattern and relationship between the creep events, moderate quakes and major events along in Guinyangan, Masbate, and northern Leyte, respectively based on the recent available seismic data and field surveys. Dislocation along a fault that involves no rapid release of energy in a seismic event is called creep. Creep was identified along the central PFZ in early 1990s using GPS records. On the other hand, moderate quakes are earthquakes with magnitude range of M5.5~M7. In central PFZ, moderate quakes were recognized to occur along the transition zone through an event in early 2003 that was accompanied by a large ground rupture. Although moderate events have usually a calculated <M7 magnitude, the extent of the observed ground rupture indicated an earthquake with magnitude greater than M7. The moderate events in this area may have a recurrence interval of as short as 10 years. Major events, on the other hand, are devastating earthquakes at least M7. Historical events in this portion of the PFZ show that major events in the locked portion also have a relatively short recurrence interval that range from 60-100 years. The northernmost part of the central PFZ is the Guinyangan fault. This portion is considered locked and the locus of major quakes in the past. South of the Guinyangan fault is the Masbate fault. A very interesting event occurred in this fault in 2003 along the Masbate fault, a transition zone. South of this portion is the northern Leyte fault which is considered undergoing a creep activity. After the 2003 event, the Guinyangan fault was anticipated to experience some changes in local stress field. However, the temporal and spatial plots of seismicity indicate a west-northwestward propagation of seismic activity along the Sibuyan fault. Sibuyan fault is an offshore fault traversing the Sibuyan Sea and probably into Taal area and/or branches out into the southern part of Marinduque island. Considering the amount of data available and the peculiar seismic activity along the central PFZ, we try to examine the seismicity and determine if a particular seismic pattern is discernable in this region and correlating them to possible regional and local stress change in a specific portion of the PFZ. Considering the importance of the results of this study and in view of the presence of major cities and towns in southern Luzon, the Sibuyan and Guinyangan faults need more attention for seismic and crustal deformation studies. Concerning the disaster mitigation and preparedness in the southern Luzon regions, finding from such researches would be an important input for local stress change research that could reveal the probability of local earthquake occurrence. Keeping in mind that the San Andreas fault has almost the same features, a comparison would be undertaken to note any similarities or differences between the two structures.
DE: 7221 Paleoseismology (8036)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7299 General or miscellaneous
DE: 8164 Stresses: crust and lithosphere
SC: Seismology [S]
MN: Fall Meeting 2005