Possible northward extension of the Philippine Fault Zone offshore Luzon Island (Philippines)
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The Philippine Fault Zone, a system of left-lateral strike-slip faults traversing the length of the Philippine Islands, is associated with the oblique convergence between the Philippine Sea Plate (PSP) and the Eurasian Plate (EP). Although it is a major deformational structure within the diffuse PSP–EP convergent boundary, some of its segments, particularly its marine extensions, are not well studied. To investigate the crustal deformation in the marine prolongation of the Philippine Fault Zone offshore Luzon Island, multi-channel seismic (MCS) data, gravity data and centroid moment tensor solutions were used in this study. Focal mechanism solutions from the Global CMT catalog were inverted to determine the average principal stress directions and consequently understand the prevailing stress regime in the study area. The stress inversion results indicate that the direction of maximum compression (σ1) is 321°N, which coincides with the PSP–EP convergence direction. From the MCS profiles, the study area was subdivided into deformation zone and a relatively stable zone. Thrust faulting, folding and general uplift are observed in the deformation zone. This zone is further subdivided into the active and inactive segments. In the active segment, uplift is occurring in the submarine ridge. This deformation pattern can be related to the ongoing uplift in some regions bisected by the PFZ. The inactive segment, characterized by intense folding of the sequences and faulting of the basement and overlying sequences, is suggested as the precursor of the Philippine Fault Zone. Deformation appears to be recently shifted to the east as delineated by an uplifted N-NW trending submarine ridge offshore NW Luzon Island.
KeywordsPhilippine Fault Zone Forearc basin Strike-slip fault
The authors would like to acknowledge the scientific party of the 4th leg of the TAIGER Cruise as well as the technical staff and crew of the R/V Marcus Langseth. The assistance of the crew of the Ocean Researcher I ship during the ORI693 cruise is also acknowledged. Principal funding for this research was provided by the National Science Council of Taiwan, R.O.C. The first author is on a scholarship under the Taiwan International Graduate Program implemented by the Academia Sinica. The figures in this manuscript were mainly prepared using the GMT software of Wessel and Smith (1998).
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