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Present-Day Crustal Deformation Along the Philippine Fault in Luzon

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Present-Day Crustal Deformation Along the Philippine Fault in Luzon Journal of Asian Earth Sciences 65 (2013) 64–74 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Present-day crustal deformation along the Philippine Fault in Luzon, Philippines ⇑ Shui-Beih Yu a, , Ya-Ju Hsu a, Teresito Bacolcol b, Chia-Chu Yang c, Yi-Chun Tsai a, Renato Solidum b a Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan b Philippine Institute of Volcanology and Seismology, Quezon City, Philippines c Institute of Geophysics, National Central University, Taoyuan, Taiwan article info abstract Article history: The Philippine Fault results from the oblique convergence between the Philippine Sea Plate and the Sun- Available online 26 January 2011 da Block/Eurasian Plate. The fault exhibits left-lateral slip and transects the Philippine archipelago from the northwest corner of Luzon to the southeast end of Mindanao for about 1200 km. To better understand Keywords: fault slip behavior along the Philippine Fault, eight GPS surveys were conducted from 1996 to 2008 in the Philippine Fault Luzon region. We combine the 12-yr survey-mode GPS data in the Luzon region and continuous GPS data GPS velocity in Taiwan, along with additional 15 International GNSS Service sites in the Asia-Pacific region, and use the Crustal strain GAMIT/GLOBK software to calculate site coordinates. We then estimate the site velocity from position Interseismic deformation time series by linear regression. Our results show that the horizontal velocities with respect to the Sunda Dislocation model Block gradually decrease from north to south along the western Luzon at rates of 85–49 mm/yr in the west–northwest direction. This feature also implies a southward decrease of convergence rate along the Manila Trench. Significant internal deformation is observed near the Philippine Fault. Using a two dimensional elastic dislocation model and GPS velocities, we invert for fault geometries and back-slip rates of the Philippine Fault. The results indicate that the back-slip rates on the Philippine Fault increase from north to south, with the rates of 22, 37 and 40 mm/yr, respectively, on the northern, central, and southern segments. The inferred long-term fault slip rates of 24–40 mm/yr are very close to back-slip rates on locked fault segments, suggesting the Philippine Fault is fully locked. The stress tensor inversions from earthquake focal mechanisms indicate a transpressional regime in the Luzon area. Directions of r1 axes and maximum horizontal compressive axes are between 90° and 110°, consistent with major tec- tonic features in the Philippines. The high angle between r1 axes and the Philippine Fault in central Luzon suggests a weak fault zone possibly associated with fluid pressure. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction (Chamot-Rooke and Le Pichon, 1999) showed the Sunda Block to be a distinct entity and rotates clockwise with respect to the Eur- The Philippine archipelago is a deformed orogenic belt resulting asian plate (Chamot-Rooke and Le Pichon, 1999; Michel et al., from the collage and collision of blocks of oceanic and continental 2001). Simons et al. (2007) used a decade (1994–2004) of GPS data affinities (Karig, 1983). It is wedged between two converging to characterize the Sunda Block boundaries and derived the rota- plates: the oceanic northwest-moving Philippine Sea Plate in the tion pole at 49.0°N–94.2°E, with a clockwise rotation rate of east and the Sunda (Sundaland) Block/Eurasian Plate in the west 0.34°/Myr. The convergence rate of about 80–90 mm/yr between (Fig. 1). The east-dipping Manila Trench forms part of its western the Philippine Sea Plate and the Eurasian Plate has been reported boundary and together with the Negros-Sulu-Cotabato Trench, ab- from the plate model (Seno et al., 1993) and Global Positioning Sys- sorbs the convergence along the western side. The northwestward tem (GPS) (Yu et al., 1999). The oblique convergence between two motion of Philippine Sea Plate is absorbed in part, by the subduc- plates is decomposed into a trench-parallel component of 20– tion of west-dipping Philippine Trench and the East Luzon Trough 25 mm/yr on the Philippine Fault (Barrier et al., 1991) and a in the east, and in another by the Philippine Fault. Recent data de- trench-perpendicular component of 40–90 mm/yr on the Philip- rived from GPS (Rangin et al., 1999; Simons et al., 1999; Kreemer pine and Manila Trench (Megawati et al., 2009). et al., 2000; Bacolcol et al., 2005) and earthquake slip vectors The Philippine Fault is a sinistral strike-slip fault which tran- sects the Philippine archipelago from north to south for about 1200 km. In spite of its recognition as a major geological structure ⇑ Corresponding author. Address: Institute of Earth Sciences, Academia Sinica, and sources of destructive earthquakes (Ms 7.5 1973 Ragay Gulf P.O. Box 1-55, Nankang, Taipei 115, Taiwan. Tel.: +886 2 2783 9910x416; fax: +886 earthquake; Ms 7.9 1990 Luzon earthquake; Ms 6.2 2002 Masbate 2 2783 9871. earthquake), a number of characteristics, e.g., precise fault location, E-mail address: [email protected] (S.-B. Yu). 1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2010.12.007 S.-B. Yu et al. / Journal of Asian Earth Sciences 65 (2013) 64–74 65 Fig. 1. Tectonic setting in the Philippines. The black barbed lines denote the major trenches. The Philippine Fault (solid line in the middle) transects the Philippine archipelago from the northwest corner of Luzon to the southeast end of Mindanao for about 1200 km. segmentation, fault slip rates, seismicity, and earthquake recur- with slip rates of 23 and 36 mm/yr found in Masbate and Leyte rence intervals, are poorly understood. (Fig. 1), respectively (Bacolcol, 2003; Bacolcol et al., 2005). On the The first quantitative measurement along the Philippine Fault other hand, the slip rate of the Philippine Fault is about 17– was in Mindanao Island wherein a left-lateral displacement of 31 mm/yr in the Luzon area (Yu et al., 1999). Geological and pa- about 28 km was found (Gervacio, 1971). Since then, studies on leo-seismological investigations indicate that the slip rate on the the motion of the Philippine Fault have been proposed using vari- Philippine Fault near central Luzon is generally between 9 and ous approaches (Acharya, 1980; Karig, 1983; Hirano et al., 1986; 17 mm/yr (Daligdig, 1997), which is lower than the value computed Pinet, 1990; Barrier et al., 1991; Aurelio, 1992; Duquesnoy et al., from GPS data. This discrepancy will be discussed in Section 5. 1994; Galgana et al., 2007). Based on GPS measurements, Duques- The area of interest in this study is the segment of Philippine noy et al. (1994) infer the slip rate of 26 ± 0.1 mm/yr on the creep- Fault in the Luzon Island, north of the Philippine archipelago. Lu- ing section of the Philippine Fault near the Leyte Island, consistent zon is part of the N–S trending Luzon arc, a 1200 km chain of 66 S.-B. Yu et al. / Journal of Asian Earth Sciences 65 (2013) 64–74 Fig. 2. An example of ITRF2005 GPS position time series for east, north and vertical components at station LUZE. Black dots with error bars show observed daily coordinate values and one standard deviation, respectively. Red dots are model predictions from linear regression. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) mostly late Tertiary to Quaternary volcanics that extends from the 45 km-long to the north of the mapped rupture based on geodetic Coastal Range of Taiwan (24°N) to Mindoro (13°N). In Luzon, the constraints. Daligdig (1997) examined geomorphic and paleoseis- Philippine Fault acts as the tectonic boundary that separates the mic data and found a recurrence interval of about 300–400 yrs Northern Luzon volcanics and Eastern Luzon metamorphics from along the Digdig Fault. the Zambales-Angat ophiolites (Karig, 1983; Karig et al., 1986). Using satellite imagery, digital elevation models, and geophysi- The Philippine Fault branches into several splays in central Luzon, cal data, Galgana et al. (2007) delineated six tectonic blocks in Lu- including the San Jose Fault, the San Manuel Fault, the Gabaldon zon and utilized a combination of earthquake slip vectors and GPS- Fault and the Digdig Fault (Nakata et al., 1977). derived horizontal surface velocities to invert for block rotations Historic records indicate large events with M 7 on the Philip- and elastic strain accumulated on the fault. They found that block pine Fault in the Luzon area occurred in 1901, 1937, and 1973 rotations can explain the majority of regional deformation in Lu- (Acharya, 1980). The 1973 event occurred along the Guinyangan zon; while fault-locking strain still makes a significant contribu- Fault near 13°N in southern Luzon (Morante and Allen, 1973; Mor- tion to the observed GPS velocity field near the fault. The ante, 1974). The region has at least seven major events in the last Philippine Fault is locked to partly-locked in the Luzon area and two centuries with a recurrence interval of about 65 yrs (Besana the locking depth is about 25 km. and Ando, 2005). The most recent large earthquake on the Philip- In this paper, we compute velocities of survey-mode GPS sites pine Fault, the Ms 7.9 July 16, 1990 earthquake, occurred on the using data collected between 1996 and 2008 and discuss the Digdig Fault segment in central Luzon and ruptured for about implications to regional tectonics.
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