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WITHDRAWN DC or Non-DC? Exploring Uncertainties and Resolution Limitations for Source Mechanism Studies in a Complex EGS Environment

Description: 

WITHDRAWN The causal connection between high-pressure fluid injections and induced seismicity is well known. The source processes of individual microseismic events and their interaction as an ensemble are less well understood and may depend on the geological preconditions and the injection design. Two endmembers of plausible acting mechanisms are pure shear, represented by a double-couple (DC), and pure tensile opening, represented by non-DC components of the moment tensor. Between the two endmembers, there are mixed-mode events and the mixed occurrence of both shear-dominated and tensile-dominated events. Differentiating between these mechanisms and resolving the non-DC component can be challenging in many EGS. Surface monitoring might provide good azimuthal coverage but cannot record relatively small-magnitude events at depth. Borehole monitoring, while closer to the source area, may suffer from the reduced azimuthal coverage required to reliably resolve differences in the source mechanism. Most EGS projects suffer from these inherent difficulties in resolving the source mechanisms of the predominantly small-magnitude events, thereby introducing significant uncertainties in inversion results. Our limited knowledge of the velocity structure of the subsurface may also bias the result, eventually hindering the reliable resolution of non-DC and DC components. Understanding these limitations is key for following interpretations of acting larger scale processes, such as the development of a rather simple hydraulic fracture or the activation of a complex fracture network mainly driven by slip along preexisting faults and fractures.

We systematically explore these uncertainties and shed light on using full-probabilistic inversion schemes relying on first-motion polarities, amplitude ratios, spectra, and full-waveforms using real and synthetic data related to the Utah FORGE, a large-scale experimental EGS.

Session: Induced Earthquakes: Source Characteristics, Mechanisms, Stress Field Modeling and Hazards [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Peter

Student Presenter: No

Invited Presentation: 

Authors