Presenter: Chen-Tung Chung
Date: 2015/12/03
Abstract
The northeast Taiwan is undergoing the transtensional deformation in a transition zone due to the collision and subduction between the Philippine Sea plate and the Eurasian plate. The Ilan Plain is a triangular-shape flat alluvial plain located on the southwest end of the Okinawa Though which behind the Ryukyu trench-arc system is an active marginal back-arc basin. We analyze the GPS data from 33 stations observe by the Central Geological Survey to understand the crustal deformation in the Ilan Plain of NE Taiwan. The station velocities are between 1.9 mm/yr to 43.0 mm/yr in a direction between 38˚ to 143˚ relative to stable continent margin of Eurasian plate. At the north margin of Ilan Plain, the station velocities are insignificant with a magnitude of 1.9 mm/yr to 7.5 mm/yr. However, the velocities rapidly increase southward to a value of 43.0mm/yr along the southern margin of Ilan Plain. The most salient feature of the strain distribution patterns are the remarkable extensional strain rates observed in central and southern flank of Ilan Plain. The extensional rates in whole Ilan area increase from north to south and the trends changes from E-W to NW-SE direction. Besides, the seismotectonic stress inversion the focal mechanisms of earthquakes recorded by BATS network reveal two extensional regimes affect the active deformation of the Ilan area. One regime is generated by the Okinawa Though extension. The other regime is the expression of the lateral extrusion caused by the Taiwan orogeny.
Reference
Angelier, J., Chang, T.-Y., Hu, J.-C., Chang, C.-P., Siame, L., Lee, J.-C., Deffontaines, B., Chu, H.-T., Lu, C.-Y., 2007. Does extrusion occurs at both tips of the Taiwan collision belt? Insights from active deformation studies in the Ilan Plain and Pingtung Plain regions. Tectonophysics 466, 356-376.