| dc.description.abstract | Global Positioning System (GPS) has become an efficient tool for studying the seismic deformation and geodynamics. Dense continuous GPS data can be used in investigating the preseismic, coseismic and postseismic deformations. The Mw6.5 Chengkung earthquake occurred at 04:38 on 10 December 2003. The GPS observed coseismic displacements reached 126 mm and 263 mm in the horizontal and vertical components, respectively. Using the coseismic surface displacements of Chengkung earthquake, the optimal parameters of fault geometry and coseismic slip rate on the seismogenic fault are inverted by assuming a simple fault model in elastic half-space.
According to the geologically recognized fault traces, the middle Longitudinal Valley Fault (LVF) is divided into two sub-faults with two a little bit different strikes. The distribution of the aftershocks shows that the dip of the seismogenic fault is larger in the shallow part, while then become smaller in the deeper part. Therefore, we divide each segment of fault into shallow and deep subfaults with different dip-angles. In our model, we define the length of each sub-fault to be 45 km, the width of the deep ones to be 50 km, and the strikes of the north and the south ones are N25.3∘E and N22∘E, respectively. Through a series of systematic searches, the optimal solutions of the three unknown parameters, the dip of the shallow sub-faults (Dip1 = 59∘), the dip of the deep sub-faults (Dip2 = 30∘) and the depth of the interface between shallow and deep sub-faults (D = 21 km) are derived. The average slip is 166 mm; the maximum coseismic slip is 855 mm and is located 15 km to the south of the hypocenter. The GPS derived seismic moment is 3.4*1025 dyne-cm. The bootstrap method is employed to estimate the confidence intervals of the three parameters, Dip1, Dip2 and D. The optimal solutions derived from bootstrap are 59∘, 28∘ and 22 km, respectively, which are consistent with the results from the grid search. Under 95% confidence intervals, the above three parameters are ranged from 48∘to 63∘, 5∘to 35∘ and 18 to 27 km, respectively. It indicates that the deep fault dip (Dip2) is less resolvable.
For the postseismic deformation, we focus on fitting the transient decay forms of the primary (< 0.1 year) and the first four months of the postseismic data. The results show that the data are well fit by the logarithmic function a + b log10(t), during the primary of postseismic deformation. During the first four months, it is well fit by the exponential function a0 +a1 e-t/t, and the relaxation time of each component for each station are not quite the same. If we want to investigate the basic physical mechanism of postseismic deformation, more longer period of GPS data and a more sophisticated model are required in the future. | en_US |