Combining seismic reflection and refraction data to investigate tectonic features of the Luzon subduction complex south of Taiwan
Date Issued
2015
Date
2015
Author(s)
Chen, Yi-Ping
Abstract
Disastrous earthquakes (Mw>8) are mostly caused by megathrusts fault that slip along plate boundaries. Some large thrust faults, called splay faults, have been suggested to emerge from the megathrust fault to the seafloor. A major splay fault has been identified in the accretionary wedge offshore southern Taiwan. This splay fault separates a folds and thrusts dominated lower slope domain from an intensely deformed upper slope domain of the accretionary wedge. This splay fault system extends from offshore southern Taiwan to offshore southwestern Taiwan in a SSE to NNW direction, and may connect to the Chi-Shan fault onshore. As the fault plane angle is raised from a low angle megathrust fault to a high angle splay fault, this splay fault could increase the vertical displacement of the seafloor once the fault is activated, then could enhance tsunami generation. In this study, we analyze several large-offset multi-channel seismic reflection profile data and refraction data from ocean bottom seismometers across the Luzon subduction zone between 18.5 °N and 21 °N, for the purpose of having a complete description of the splay fault system and tectonic patterns of the Luzon subduction zone south of Taiwan. The results of seismic reflection profile analysis suggest that (1) the eastward dipping decollement steps down to basement at about 20 to 40 km from the trench axis; and (2) there are 1 or 2 splay faults emerging from different branching points, the fault plane angle is about 26 degrees, lower than generally thrust faults. To image the structure of the deeper crust, seismic refraction data are used to build the P-wave velocity model. P-wave velocity model shows that the Moho depth is about 15 to 17 km, and thickness of the crust is about 9 to 11 km. Integrating the results from previous studies and this study, we suggest that the structural variation of the splay fault system from 18.5 °N to 22.5 °N is connected with the trending of the Manila trench and incoming sediment supply. Examining the seismicity and seismic reflection profile data, we suggest the distribution of a possible megathrust zone in the area south of Taiwan. As there is no big earthquake record around the branching point mapped on profile MGL0905-25A at 20.7 °N, where a seamount subduction has been observed, there may be a high potential to produce large earthquakes in the future.
Subjects
Splay fault
Megathrust zone
Luzon subduction zone
Ocean-bottom seismometer
P-wave velocity model
Type
thesis
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