Investigating the Possible Role of Magmatically-Derived Fluids in Faulting in the Long Valley Caldera

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EAR0087494 (PH #37x)INVESTIGATING THE POSSIBLE ROLE OF MAGMATICALLY-DERIVED FLUIDS IN FAULTING IN THE LONG VALLEY CALDERAMark D. ZobackDepartment of GeophysicsStanford UniversityThe goal of this study is to improve our understanding of the interaction of volcanic and tectonic processes by investigating seismic activity in the Long Valley caldera, Eastern California. Specifically, we are studying the role of magmatically derived fluids in the mechanics of faulting in and near the caldera. It is well known that high fluid pressures may trigger earthquakes by decreasing the normal stress across faults. While scientists suspect that fluid pressures are high above magma chambers due to heating of ground water and exsolution of fluids from magma, a clear link between magmatically derived fluids and triggered seismicity remains elusive. By mapping the stress field and quantifying volcanically influenced pore pressures associated with faulting in the Long Valley caldera we hope to better constrain the relationship between tectonic and volcanic activities at depth.Fluids have been shown to influence a variety of faulting processes. Although earthquake triggering associated with pore fluid migration has been observed in cases of induced seismicity and has been hypothesized to occur along the San Andreas Fault, it has not been possible to quantify or map relative pore pressure changes in detail. Precise mapping of relative pore pressures associated with a spatially and temporally propagating system of earthquakes would help us understand how fluid pressures might be changing with time and diffusing through bedrock to trigger these events. This project is studying these processes in detail.