Variation of Surface Creep Rate Along the Philippine Fault Based on Surveys of Alinement Arrays and Offset Cultural Features
Abstract
The 1250-km-long, sinistral Philippine fault, an arc-parallel strike-slip fault driven by the oblique subduction of the Philippine Sea plate westward beneath the continental Sunda plate, has produced three surface-rupturing earthquakes in the past 50 years. In its central section, GPS surveys document slip rates of 20-30 mm/yr (Bacolcol et al., 2005). To document the spatial extent and rate of creep, we surveyed offset cultural features (roads, buildings, and curbs) and installed 16 alinement arrays from southern Luzon Island to northern Mindanao Island since 2013. Our observations provide the first direct evidence of surface creep along a 600-km-long section of the central Philippine fault. We surveyed offset cultural features on Leyte Island where cumulative offsets and construction dates yield creep rates of 20 mm/yr averaged over the past 10-35 years. From alinement array data, creep rate on Leyte ranges from 21-27 mm/yr, suggesting that strain release in this area is primarily by surface creep. This section has had no large historical earthquakes during the past four centuries (Bautista and Oike, 2000). In contrast, moderate to large surface-rupturing earthquakes occur on southern Luzon, Masbate, and northern Mindanao, where less creep occurs. Masbate Island was struck by the 2003 Ms 6.2 earthquake that produced a 18-km-long surface rupture with a maximum offset of 50 cm. All five measurement sites on Masbate exhibit creep; the 3-yr rate for two sites ranges from 7-17 mm/yr. In southern Luzon, our initial (1.25-yr) creep rate estimate was 8 mm/yr on the segment that ruptured during the 1973 earthquake (Ms 7.0). In northern Mindanao, we obtained 14 mm/yr rate on the segment that ruptured during the 1879 earthquake (Ms 7.4). These observations suggest that, like the San Andreas fault, the Philippine fault shows pronounced along-strike variation in seismic behavior.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T23A2907T
- Keywords:
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- 7221 Paleoseismology;
- SEISMOLOGYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8107 Continental neotectonics;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS