Testing two Mountain Building Models Using Coseismic GPS Data

Two distinct models have been advanced for the construction of mountain belts. In the decollement model, mountain belts are supposed to be critical wedges consisting of rock units that were thrust and multiplexed over a basal decollement under horizontal compression. In the thick-crust model, mountain belts are assumed to be a part of a compressed and thickened crust that rises under its own buoyancy. Here we examine the difference in coseismic response of the two models to earthquake faulting, using the coseismic GPS data collected during the 1999 Chi-Chi (Mw = 7.5) earthquake, Taiwan. Simulated surface deformation in the Chi-Chi earthquake for the two models are compared with the observed coseismic GPS data. Result for the thick-crust model shows good agreement with the observed deformation, i.e., the coseismic displacement in the upper plate decreases steeply with distance from the fault and the vertical component declines from an uplift near the fault to a subsidence at distances greater than 20 km. The decollement model, on the other hand, does not predict such pattern in the surface deformation.