Jan Vermilye

Evidence for aseismic deformation in the western Transverse Ranges, southern California: Implications for seismic risk assessment

Recent studies in southern California suggest that long-term deformation rates are far in excess of that which can be accounted for by historical seismicity, and thus, a deficit of moderate and/or large earthquakes exists in southern California. Although possible, this conclusion is not unique because aseismic deformation may have contributed to bulk regional strain. We examined Cretaceous to Pleistocene sedimentary rocks exposed in the Ventura basin along four cross-strike traverses to evaluate the possibility that aseismic deformation contributed to regional shortening. Our field and microstructural investigations suggest that aseismic deformational mechanisms, particularly pressure solution, contributed significantly to permanent shortening strain during the late Neogene and that the proposed seismic deficiency may be overestimated.

Ambient Fracture Imaging: A New Passive Seismic Method

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Forecasting reservoir performance by mapping seismic emissions

AbstractStreaming depth imaging (SDI) is a modified version of Kirchhoff migration that images the intensity and distribution of weak seismic waves emitted from rocks at depth. These images reveal the locations of the fractures and fracture networks in the reservoir. SDI allows for more informed forecasts for drilling, hydraulic fracturing, and reservoir management than is provided by traditional microearthquake mapping methods. Using passive data from surface and near-surface geophone grids, SDI integrates the seismic emissions over time to form the fracture activity volume. The fracture systems and the active production volume (APV) of the reservoir are calculated from this activity volume. In situ wellbore measurements indicate that the preexisting fracture systems in the reservoir rocks have substantial impact on the placement of the fluids during the hydraulic fracture treatment. They also strongly influence the locations of maximum oil and gas production and the decline rates of resource production....