Abstract:

Stress distribution around a source fault results from the rupture process of an earthquake. Therefore it can be key information for clarifying the rupture process of the fault. Moment tensor inversion is a powerful technique to determine principal stress orientations in the vicinity of a source fault. However, this technique determines only the orientations and regimes of principal stresses on the fault plane and has no ability to measure the stress far from the fault plane. In this study, we present one of the stress measuring methods which can determine stress far from source fault, diametrical core deformation analysis (DCDA). We have applied this method to the boring cores from a borehole penetrating the Futagawa fault, Kumamoto, Japan, which is one of the source faults of the 2016 Kumamoto earthquake sequence. Preliminary results of the DCDA curried out for limited core samples show core diameter deformation data is effective to figure out stress data.

1 Introduction

There is strong relationships between earthquake and in-situ stress of the rocks around the source fault (Hardebeck, 2004, 2012; Stein, 1999). In particular, stress distribution around a source fault after an earthquake results from the rupture process of the source fault. Therefore information on in-situ stress of rocks around the source fault becomes a clue to clarifying the rupture process of the fault.

Moment tensor inversion is a powerful technique to determine principal stress orientations in the vicinity of a source fault. However, this technique determines only the orientations and regimes of principal stresses on the fault plane and has no ability to measure the stress far from the fault plane. In this study, we present one of the stress measuring methods which have the ability to determine one dimensional stress distribution (i.e. depth profile of stress) and the magnitude of differential stress: diametrical core deformation analysis (DCDA).

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