Investigation of the discrepancy in the earthquake magnitude values reported by different agencies in the Western Canada Sedimentary basin

Abstract

Earthquake magnitude plays a crucial role in assessing ground shaking severity and formulating mitigation strategies for both natural and induced earthquakes. This study specifically focuses on the Western Canada Sedimentary Basin (WCSB) and examines the estimation of local magnitude (\({M}_{L}\)) by different agencies. The analysis includes the application of various distance calibration functions for the Richter’s methodology, incorporating both Richter's original function (Richter, Elementary Seismology, Freeman, San Francisco, Calif, 1958) and WCSB-specific calibration functions proposed by Yenier 2017 Bull Seismol Soc Am 107:1421-1431 and Babaie Mahani and Kao 2019 Seismol Res Lett 90:203-211, 2020 CSEG Recorder 45:12.

In the WCSB, fluid injection has caused significant increase in the rate of seismicity in several localities, prompting the regulatory agencies to request suspension of injection operations after the occurrence of red-light (i.e., \({M}_{L}\) ≥ 4) events. Our investigation, based on a new dataset, sheds light on the significant effects due to distance calibration functions on the \({M}_{L}\) estimation. Notably, we observe that using the original Richter’s calibration function designed for southern California results in more than three times the number of red-light events compared to employing more appropriate calibration functions. Our results point to the unnecessary economic consequences when exaggerated \({M}_{L}\) values are used in the regulatory process and underscores the need for adopting proper calibration functions for seismic monitoring in the WCSB.