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Seismic emissions reveal the mechanical stratigraphy of the Middle Paleozoic section under the Appalachian Plateau, Pennsylvania

Publication Date Jun 21, 2022

Abstract

ABSTRACT The Middle Paleozoic section of the Appalachian Plateau exhibits a mechanical stratigraphy defined by layers that emit seismic energy with unique signatures in response to a strain energy accumulated on time scales associated with local, regional, and plate-scale processes. The Earth is in a state of frictional equilibrium, which means that even small changes in effective stress cause brittle failure and the concomitant release of ambient seismic energy. Stress changes as low as 0.001 MPa, the level of stress changes during Earth tides or the transmission of a fluid pressure wave, can activate failure on critically oriented fractures. These phenomena lead to a release of ambient seismic energy, which can be mapped using seismic emission tomography (SET) methods to image fracture networks emitting coherent seismic waves. We used a buried array of 54 sondes to identify active fracture networks over a contiguous volume of 3.76 km3 within Middle Paleozoic rocks hosting two Marcellus gas shale wells drilled under the Appalachian Plateau of Lycoming County, Pennsylvania, USA. We sampled ambient seismic emissions before and after two stimulations and found that the pattern was repeatable. The fracture patterns illuminated by ambient seismic emissions defined a mechanical stratigraphy populated by clouds of seismic activity separated by packages of beds emitting relatively less seismic energy. The unique attribute of the beds emitting less seismic energy is a lower least horizontal stress (Shmin) relative to ...

Concepts

Appalachian Plateau Seismic Emissions Seismic Emission Mechanical Stratigraphy Release Of Seismic Energy Seismic Emission Tomography Changes In Effective Stress Seismic Energy Release Of Energy Silurian-Devonian Carbonates

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No potential conflict of interest was reported by the authors. The conception and design of the study, acquisition of data, analysis and interpretatio...

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