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Double-Pair Double-Difference Relocation for Dense Network Improves Depth Precision of Induced Seismicity, Leading to a Detailed 3D Fault Geometry Model

Description: 

Earthquake locations with well-constrained uncertainties allow for interpreting fault systems and fault activation mechanisms for large datasets. Improved precision and reduced uncertainty of relative locations can aid in understanding fault plane geometry and provide images of fault activation from induced seismicity. Double-pair double-difference relocation is an adaptation of event-pair relocation that incorporates station-pair differential travel times, which is particularly useful for dense networks. The additional information from station pairs limits the impact of velocity model uncertainties, reducing the impact of velocity model errors in locations. For reservoir applications with induced seismicity, this benefit is pronounced at depths where large velocity contrasts due to reservoir layers occur. In such areas, source locations can be poor from the traditional event-pair relocation method. We present double-pair double-difference relocation results for 4,000 induced events from monitoring near Fox Creek, Alberta. Because of highly correlated waveforms with a 0.9 cross-correlation coefficient cut-off, including station-pair information increases data from 2.5 million cross-correlation differential times to 62.8 million data points. The relative uncertainties in the double-pair relocated catalog are zero-mean and 1-2 m for all three spatial parameters, which improves upon the event-pair relocations with relative uncertainties of 3 m in X and Y and 4 m in depth and nonzero means in the range of 50 m in Y and 100 m in Z due to directional anisotropy. Double-pair relocations lead to spatial clustering of events at discrete depths, which is consistent with the geology of the stimulated zone, comprising thin layers of stronger carbonates embedded within weaker shales. Using double-pair double-difference, we provide a precise fault map, including 3D least-squares planar fits for earthquake clusters. The fault map confirms prior studies about existing faulting in the region, particularly that the study area is part of a larger structural corridor, likely a flower structure exhibiting Riedel shear behavior.

Session: Induced Earthquakes: Source Characteristics, Mechanisms, Stress Field Modeling and Hazards - III

Type: Oral

Date: 5/1/2024

Presentation Time: 02:30 PM (local time)

Presenting Author: Katherine

Student Presenter: Yes

Invited Presentation: 

Authors