Introduction

In volcanic areas, deviations from the usual double-couple (DC) model of shear faulting may be able to illuminate a link between the source process of an earthquake and fluids associated with the geothermal or magmatic system. These non-double-couple (non-DC) earthquakes have mechanisms vastly different from simple shear along a linear fault plane and are characterized by a compensated-linear-vector-dipole (CLVD) component, suggesting either fluid involvement or complex shear failure, and/or an isotropic component which describes volume changes in the source region.

In this study, we investigated the source kinematics of events greater than M3.5 occurring between 1993 - 2003 within a 100 km wide circular area centered at the Long Valley caldera, which includes the Mono-Inyo Craters to the north and the Sierra Nevada Block to the south, to identify events with significant coseismic volume changes. In this active geothermal and magmatic area, we treat coseismic volume changes as an indicator of fluid involvement at the source.

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