Analysis of coseismic deformation using EOF method on dense, continuous GPS data in Taiwan

Taking advantage of the dense continuous GPS network data, we demonstrate the effective utility of the method of empirical orthogonal function (EOF) in obtaining the coseismic deformation (vector) field on the crustal surface caused by significant earthquakes. We conduct case studies w.r.t. two earthquakes that have occurred in Taiwan: one off the east coast of Taiwan in 2002 (Event I, Mw 7.1) and one inland in southern Taiwan in 2010 (Event II, Mw 5.7 or 6.3). We demonstrate that, superior to the simple least-squares estimates obtained directly from individual GPS position time series, the EOF analysis is capable of extracting the coseismic deformation in the form of coherent spatial pattern and time evolution. The prevalent common-mode errors in the GPS data are also well resolved as distinctive and separate EOF modes. The extracted coseismic spatial patterns provide evidences linking the regional tectonics with the orogenic process in Taiwan under the plate convergence. We further contrast our EOF results against those calculated via idealized elastic dislocation models, and find notable discrepancies especially for the far field, which can be attributed to the complexity of the tectonic environment of Taiwan.