Interseismic crustal deformation in the Taiwan plate boundary zone revealed by GPS observations, seismicity, and earthquake focal mechanisms

Interseismic crustal deformation in the Taiwan plate boundary zone revealed by GPS observations, seismicity, and earthquake focal mechanisms Interseismic crustal deformation in the Taiwan plate boundary zone revealed by GPS observations, seismicity, and earthquake focal mechanisms, Tectonophysics This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract 9 We use GPS-derived surface velocities, seismicity, as well as estimates of earthquake focal 10 mechanisms from the time period before the 1999 Chi-Chi earthquake to evaluate spatial variations of 11 surface strain rate and crustal stress regime in the Taiwan plate boundary zone. We estimate strain rates 12 with a new but simple approach that solves for surface velocity on a rectangular grid while accounting 13 for the distance between observations and each grid node and the impact of a spatially variable density 14 of observations. This approach provides stable and interpretable strain-rate estimates. In addition, we 15 perform a stress tensor inversion using earthquake focal mechanisms determined by P waves 16 first-motion polarities. Our estimates of the principal orientations of two-dimensional surface strain rate 17 tensor generally agree with the inferred orientations of the stress axes. This agreement suggests that a 18 large scale variation of stress orientations from the surface to the base of the crust is insignificant and 19 the predicted faulting style is consistent with stress buildup during the interseismic loading. We find 20 that the geometric configuration of the Chinese continental margin alone can not fully explain the 21 distribution of maximum contraction and compressive axes in Taiwan. Distribution of seismicity and 22 focal mechanisms before and after the Chi-Chi mainshock suggest that the maximum principal stress 23 axis is vertically-oriented in the Central Range; in contrast to the horizontal maximum principal stress 24 axis in western Taiwan and the Longitudinal Valley. Extension in the Central Range reflects the 25 consequence of exhumation and crustal thickening. 26