GPS Strain Rate and Seismic Activity Before the Ludian Earthquake (Ms 6.5), Northeast Yunnan, China: New Implications for Eastward Chuan-Dian Block Extrusion

  • A set of conjugated strike slip faults are assessed outside the Chuan-Dian Block
  • Eastward extrusion of the Chuan-Dian Block is constrained by GPS analysis
  • Strain accumulation status before the Ludian earthquake is quantified

We characterized E-W shortening crustal deformation using GPS measurements and an earthquake focal mechanism solution to estimate conditions before the Ms 6.5 Ludian earthquake of 3 August 2014 (16:30, UTC+8). A series of NW-SE striking transpressive faults are distributed outside the Chuan-Dian Block. They accommodated the E-W shortening and N-S stretching in this region resulting from Chuan-Dian Block outward expansion. The displacement velocity field about the eastward, fault-normal slip rate and the vertical component are also examined. The results show that they share a similar rate change at the Anninghe, Zemuhe, Puxionghe, Jiaojihe, and Baogunao-Xiaohe faults. Among these faults, the maximum thrusting slip rate of the Baogunao-Xiaohe fault is less than 4 mm yr-1. The slip rate change may represent a transition from lateral translation into a vertical thrusting movement. Furthermore, counterclockwise rotation also plays an important role in absorbing the E-W shortening. Relative to the inner zone, the outer Chuan-Dian Block together with the Daliang Shan fault zone represent the development of a new deformation area. A prediction could be made that the Daliang Shan fault zone will eventually replace the east boundary fault role of the Anninghe-Zemuhe-North Xiaojiang fault due to Chuan-Dian Block continuous outward expansion.

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