Double-Difference Seismic Event Relocation: A Study of the Applications and Limitations of the Relocation Problem
Date
2024-08-12
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Abstract
Earthquake relocation provides refined earthquake catalogs based on additional considerations or data beyond the initial earthquake location estimates. Double-difference relocation, in particular, utilizes the assumption that ray paths in close proximity to one another will pass through a similar earth velocity structure. The method minimizes the residual difference for pairs of these travel time observations to refine event locations. This thesis focuses on the application of three double-difference methods based on differing geometries of data pairing: event-pair relocation, station-pair relocation, and double-pair relocation. In this thesis, I introduce a previously unavailable software, relocDD-py, that implements all three of these relocation methods along with a complete workflow, including data preparation, automated variable selection, and post-relocation uncertainty analysis. This software is developed in Python using many widely implemented Python packages to allow for integration into existing seismic workflows. In addition, I present studies that apply this software and methodology at various scales, including (1) a large-scale tectonic study of complex plate subduction and the resulting seismicity in Alaska and Yukon where we find direct evidence of the Totschunda-Fairweather Connector fault; (2) a regionally observed induced seismicity event with analysis of the entire earthquake sequence from Peace River, Alberta where we find activation of multiple sub-parallel faults; and finally (3) a densely monitored induced seismicity experiment which ruptured a complex network of pre-existing faults near Fox Creek, Alberta where we find limits on the depth of seismicity to the hydraulic fracturing depth. Double-difference relocation can improve existing catalogs even in sparsely monitored areas and can reduce relative location uncertainty to such a degree that detailed three-dimensional interpretation of fault structures is possible. In many cases, event-pair relocation, the most widely applied double-difference method, is sufficient to improve relative uncertainties and maintain absolute location uncertainties. However, in cases with complex velocity models and dense monitoring, the double-pair method can improve relative uncertainties beyond event-pair relocation, which may identify additional seismicity features. The double-pair method is more computationally expensive and, therefore, is not necessary in all cases. All three double-difference relocation methods have an important role to play in earthquake and other seismic event relocation and catalog refinement. My work provides a software tool and a standardized workflow for the implementation of double-difference relocation in seismic studies.
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Keywords
seismology, earthquakes, tectonics, induced seismicity, earthquake source studies, earthquake location
Citation
Biegel, K. M. (2024). Double-difference seismic event relocation: a study of the applications and limitations of the relocation problem (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.