Seismological evidence of simultaneous mountain-building and crust-thickening from the 1999 Taiwan Chi-Chi earthquake (Mw=7.6)

High-quality seismic data recorded during the 1999 Taiwan Chi-Chi earthquake (Mw=7.6) show that a small-scale orogenic process of both mountain-building and crust-thickening was simultaneously accomplished along one set of crustal-scale conjugated faults. Mountain-building near the surface was primarily produced by the main shock along an eastward low-angle thrust fault in the upper crust. In the meanwhile, a sequence of aftershocks along a westward high-angle reverse fault in the lower crust could increase crustal thickness even though major crustal deformation in generally taken place under ductile deformation. Also, velocity structures inverted from seismic tomography suggest that the crustal deformation in the form of both mountain-building and crust-thickening has been repeatedly generated by a similar orogenic process during the past million years. The dynamic dual process observed here contributes to the growth of the orogenic zone in the near the surface and deep crust in Taiwan.