Kinematic crustal deformation features of Wenchuan earthquake obtained by GPS

Abstract

Global Positioning System (GPS) plays an important role in monitoring crustal deformation. Traditional methods for GPS crustal deformation monitoring is mainly based on static positioning, which cannot be used to obtain instantaneous crustal deformation. To monitor crustal deformation in Sichuan, 12 continuous operation GPS reference stations (CORS) have been setup in Sichuan, China. There are 5 GPS stations located at the east side of Longmen mountain fault. GPS data for a period of about 60 seconds has been recorded during Wenchuan earthquake. Using data with 1-second interval from Sichuan GPS network, we compute the kinematic crustal deformation caused by MS 8.0 Wenchuan earthquake to study the crustal deformation characteristics during Wenchuan earthquake. GPS baselines before and after the earthquake were processed by GAMIT, and then the coordinates of all stations were combined by GLOBK using China local frame. After selecting relative stable points from the 12 GPS stations based on GPS data of 4 consecutive days from May 11 to May 14, 2008, we have obtained the kinematic crustal deformations lasting about 60 seconds by using Yaan as a reference station. Results show that the principal displacement direction of the stations in Sichuan GPS network was approximately orthogonal to Longmen mountain fault direction. The principal deformation pattern was expansion towards northwest with periodical vibrations. Mianyang's maximum kinematic horizontal displacement was 49.2cm towards NW50°, Pixian's maximum kinematic horizontal deformation was about 114.1cm towards NW45° and Chengdu's deformation was 21cm toward NE45°. Decomposing the deformation series into Longmen mountain fault direction and its orthogonal direction, the kinematic deformation features of several stations were obtained. Results also show that Mianyan and Pixian moved towards Northwest with small amplitude of swinging during the earthquake. The height of Mianyan decreased 2 cm after uplifting 10 cm in the vertical direction. The height of Pixian fluctuated periodically and the fluctuation range was about ±13 cm.