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2014/10/28 14:00 Prof. Char-Shine Liu（Institute of Oceanography, NTU）
Seminar
Poster： ╱ Post date：2014-10-22NCU IHOS Seminar Announcemnet
Speaker：Prof. Char-Shine Liu
Place：S-325, Science Building 1
Abstract：
Title：Tectonic Features and Megathrust Fault Offshore South Taiwan
Speaker：Prof. Char-Shine Liu
Institute of Oceanography, NTU
Time：10/28（Tue.）14：00
Place：S-325, Science Building 1
Abstract：
Historical record of significant disastrous earthquakes (Mw>8) has mostly been regarded as megathrust earthquakes that slipped along the interface of underthrusting plate and overriding plate. This kind of thrust is thought to be the seismogenic zone of great earthquakes. Stresses between two plates can be easily accumulated in this zone, and sea floor may rupture during the co-seismic slip of the megathrust, generating great tsunami. The Luzon subduction system between Taiwan and Luzon islands has been categorized as one of the highest tsunami risk zones in the circum-Pacific region. This subduction system forms the boundary between the Philippine Sea Plate and the Eurasian Plate in this region. It can be divided into four major morphotectonic belts from west to east: Manila Trench, accretionary wedge, North Luzon Trough and Luzon volcanic arc. The accretionary wedge can be further divided into a lower slope domain and an upper slope domain by a prominent megathrust thrust. This megathrust fault forms the boundary separating a fold-and-thrust belt lower slope domain of the accretionary wedge from an intensely deformed upper slope domain. This megathrust fault extends laterally over 250 km in the offshore region, from south of 20oN northward to the onshore structure of southwestern Taiwan, and is suggested to be the major branch of the splay fault system of the Luzon subduction zone.
In order to better understand the structure features of this megathrust fault and its variations from south to north, as the tectonic processes changes from subduction in the area offshore south Taiwan to collision on land Taiwan, we analyze a series of large-offset deep seismic reflection profiles collected during the TAIGER survey in 2009 that ran across this megathrust fault system. Decollement has clearly been observed below the lower slope domain of the accretionary wedge. The range of the decollement increases from south to north, inferring that the continental materials have been carried into the subduction zone and the subduction angle decreases from south to north. Two or three thrusts branching out from the megathrust and not connected to the decollement. These thrusts may extend to the sea floor, and they are so-called megasplay faults. There is no obvious change on the branching point and megasplay fault position from subduction to incipient collision. The existence of the gigantic thrust represents this area have high potential of seismic and tsunami threat.
Last modification time：2014-10-22 AM 11:09
