GPS-derived crustal deformation in southwestern China

Abstract

The Sichuan – Yunnan region is divided into nine active secondary crustal blocks, based on several GPS repeat surveys at more than 200 GPS sites during the period 1999 – 2005. Velocities of the nine secondary blocks are calculated and analysed. The strain field within the area related to the 2004 Sumatra – Andaman earthquake event is also analysed. Results indicate that the crustal movement in the northern and western areas of the Sichuan – Yunnan region is stronger than that in the south and east. The horizontal velocities change from 19 – 20 mm/y in the northern and the central rhombic block to 11.7 mm/y in the southern rhombic block. The orientations of block motion vary from 99° in the north to 126 – 150° in the central area and 156 – 188° in the south, implying that the motion of the Sichuan – Yunnan rhombic block is dominated by a clockwise rotation. The velocity differences between blocks inside and outside the rhombic block are about 6.5 – 7.7 mm/y in the northern and central Sichuan – Yunnan region. The southeastward extrusion rate of the Tibetan Plateau shows a remarkable downtrend of up to 47% along the Xianshuihe Fault, suggesting an increase in strain accumulation and hence an area prone to strong earthquakes. The horizontal coseismic deformation caused by the Mw9.0 Sumatra – Andaman earthquake is <10 mm with a south-southeast orientation towards the earthquake epicentre. The dilatational strain rates from coseismic displacements reveal a possible interaction between the extrusion from the Tibet plateau interior and the underthrust effects from the Sumatra – Andaman earthquake.

Key words:

• crustal deformation
• GPS
• rhombic block
• Sichuan – Yunnan region
• Sumatra – Andaman earthquake

Acknowledgements

We would like to thank the journal reviewers for their constructive comments. We are very grateful to all members involved in the GPS field surveys. This work was supported by National Natural Science Foundation of China (40304002), CMONOC and the Major State Basic Research Development Program of China (973 Program 2004CB418403).