Q(Subscript p)Structure in the Taiwan Area and Its Correlation to Seismicity

The active Quaternary deformation of the Pakua anticline area in theforeland belt of western Taiwan has been examined based on field investigationas well as paleostress analysis.The strata exposed in the Pakua areaare composed of Quaternary molasse sediments of conglomerate and sandor sandstone(Toukoshan Formation).The seismic reflection profiles showthat the main structure of this area is characterized by frontal thrust(theChanghua Fault)and the associated anticline fold(the Pakua anticline).Three principal deformation structures at outcrop scale have been recognized:(1)compressional fracture of pebbles,(2)strike-slip fault,and(3)normal fault.It indicates that the Pakua anticline area has experienced acomplex history of tectonics including different stress regimes of contraction,strike-slip and extension.The study of paleostress shows:(1)compressionin a WNW direction as deduced from both the fracturing of pebblesand strike-slip faults;and(2)the occurrence of E-W and N-S extensionaccommodated by normal faulting,especially in the northern part of thePakua anticline area.The WNW compression,being perpendicular to thetrend of the frontal thrust and the regional major folds,represents the regionalcompressional stress direction in the foreland of Taiwan.The normalfaulting in this fold-and-thrust belt suggests that the importance of theforce of uplift/gravitation resulted from the release of the frontal thrustingand/or the transtensional stress regime of possible regional transfer faults.

並列關鍵字

Q(Subscript p)Structure ； Attenuation Time Values ； Seismicity

國際替代計量

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