Stress state along the Anninghe-Zemuhe fault zone, southwestern China, estimated from an array of stress orientation measurements with a new method

Abstract

Measurements of in-situ stress orientations at relatively shallow depths were conducted at 11 sites along the Anninghe-Zemuhe fault zone, southwestern China, with a newly developed method. The Anninghe fault in the fault zone has been considered to have a potential for a large earthquake with a magnitude of about 7.5, while the Zemuhe fault shows very little such potential. The present study has mainly two objectives: one is to show new data of the spatial distribution of the stress orientations around the fault zone, which is obtained directly from the measurements; the other is to examine the possibility to detect a stress pattern in relation to the past activities of earthquakes along the fault zone. The observed principal stress orientations are distributed between the NNW-SSE and NW-SE directions, which is consistent with the earthquake focal mechanism solutions near the fault zone. On the other hand, it is unclear whether the observed stress pattern is related to past activities of the fault zone, since the data fluctuation was too large to determine this. We note that the stress orientations are favorable for slip on the Anninghe fault, while being unfavorable on the Zemuhe fault, from the present experimental data.