Crustal deformation of the Mud stone area in SW taiwan using the geodetic data from 2002 to 2010

The previous geodetic study results of the Parkfield segment of the San Andreas fault in California and the Chihshang fault in eastern Taiwan indicate that the creeping fault still has the potential to generate large earthquakes. High strain rate of ∼1.0 μstrain/yr in mud stone area in SW Taiwan shown by previous geodetic data may imply high earthquake potential. However, the historical earthquake records represent no significant earthquakes occurred in this area since 1900. In this study, we therefore mainly adopted the measurements from 201 campaign-mode GPS stations and 2 nearly E-W-trending precise leveling routes to estimate the characteristics of main faults (the Chishang fault and Hsiaokangshan fault) and their earthquake potentials in the mud stone area in SW Taiwan. Similar elevation change patterns of six repeated leveling surveys between 2002 and 2010 from these two routes imply that the vertical deformation rate in this area is stable. The leveling vertical velocities west of the Hsiaokangshan fault are almost zero while the velocities east of the Hsiaokangshan fault rapidly increases to 15-20 mm/yr. Then the rates rapidly decrease to almost no vertical motion. The GPS horizontal velocity field from 2002 to 2010 shows ∼60 mm/yr, N267° east of the Chishan fault. Then the horizontal velocities west of the Chishan fault gradually decrease westward to ∼11 mm/yr, N264°. Comparing the horizontal and vertical velocity patterns, we notice that the obvious velocity gradient is shown in the area between the Hsiaokanshan and the Chishan fault. Due to the major faults in Taiwan mainly dipping to the west, we preliminarily propose that the high strain rate in mud stone area in SW Taiwan results from the motion of the Hsiaokanshan fault. In the future, we will use the 2D fault model to evaluate the fault parameters and to estimate the seismic potential in this area.