Collision is among the important processes for the growth of continents, and the way in which subduction becomes a collision is still an active research topic. Here, I examine the seismogenic structures of southern and central Taiwan where the subduction along the Manila Trench has terminated and given way to an arc-continent collision on land. Based on focal mechanisms and seven finite-fault slip models, coseismic tectonic extrusion is active in this region, in which the basement highs on the incoming passive margin are acting as indentors and strongly modifying the seismic moment release patterns in the collision zone. At least three magnitude 7 earthquakes have ruptured both north and south of an indentor called the Peikang high in the past hundred years. After examination, the basement highs show little global positioning system (GPS)–recorded relative motion with respect to the incoming passive margin; high Bouguer gravity anomalies associated with denser materials of the basement; and low heat flow due to less dewatering and exhumation. With regard to seismogenic structures, faster GPS relative motions, lower Bouguer gravity anomalies, and higher heat flow characterize the regions surrounding the indentors. Similar processes might be operating in other arc-continent collision zones. For other regions where there are fewer seismic instruments to monitor earthquakes, it might be helpful to combine a geological survey with gravity and other geophysical data sets to help identify such potential seismogenic structures.
- Received 16 December 2011.
- Revision received 30 July 2012.
- Accepted 2 August 2012.
- © 2011 Geological Society of America