Co-Seismic Indentor-Related Deformation during the Termination of Subduction and its Associated Geophysical Characteristics: An Example from Taiwan

Collision is among the important processes for the growth of continents, and how subduction becomes a collision is still an active research topic. Here we 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, co-seismic tectonic extrusion is active in this region in which the basement highs on the in-coming passive margin are acting as indentors, and strongly modify 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 last hundred years. After examination, the basement highs show little GPS-recorded relative motion with respect to the incoming passive margin; high Bouguer gravity anomaly 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 anomaly, and higher heat flow characterizes 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 datasets to help identify such potential seismogenic structures.