Fault-valve behaviour and episodic gas flow in overpressured aquifers-evidence from the 2010 Ms5.1 isolated shallow earthquake in Sichuan Basin, China

Abstract

We investigated the 2010 Ms5.1 Suining earthquake (a temporally and spatially isolated event) centred in Moxi gas field in the tectonically stable central region of Sichuan Basin, China. The focal depth is estimated to be approximately 2.8 km and thus the earthquake is nucleated in Triassic marine sediment, coincident with the depths of the top boundary of an overpressured gas reservoir. The strike/dip/rake of the estimated source fault is 223/48/122, showing a rupture area of a dimension of 2.4 km along a blind reverse fault in agree with the geological structures and regional stress regime of this area. Through an integrated analysis, we propose that the associated fault slip of this earthquake was most probably initiated and driven by gas injection from the underlying overpressured reservoir into the shallower gas reservoirs. No aftershocks following the Suining earthquake indicates that the gas injection from the deeper reservoir is somewhat episodic and a fault-valve behaviour.