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Extending Coda Envelope Moment Magnitudes to Remote Regions of Canada for Improved Hazard Assessment

Description: 

To achieve uniform seismic hazard assessment throughout a region, it is crucial that the input parameters are uniform. Canada is a tectonically diverse country with non-uniform seismicity and station coverage. Although modern hazard assessment tools are able to consider multiple input parameters, magnitude recurrence rates remain the backbone of seismic hazard calculations. A first step toward uniformity of magnitudes in Canada was the development of conversion relations to convert the myriad of magnitude types in the database to moment magnitude. However, the conversion relations are based on moderate to large events and may not be valid for smaller earthquakes, which control the shape of the recurrence curve. The coda envelope moment magnitude method (Mayeda et al, BSSA, 2003) proved successful in lowering the moment magnitude threshold for direct calculation from ~3.5 to ~1.5 in the seismically active regions of southeastern Canada, below the M2.5 minimum used in hazard assessment in Canada. Thus, the reliance on converted magnitudes has been reduced. The need cannot be completely eliminated as the coda envelope method cannot be used for analog data unless it is digitized. The method requires calibration on a regional scale and thus the calibration for one region cannot be applied to another, which may have different attenuation and stations. Extension of this method into the adjacent Appalachian region was also successful. The use of this method has been extended to remote and/or less active regions of eastern Canada: the northern Canadian Shield, the Arctic and the eastern offshore (Laurentian Channel and Labrador Sea). Challenges in these regions include sparse station coverage and small numbers of suitable ground truth events. In the offshore regions, it is also critical to separate those events occurring in continental and oceanic crust as the coda consists predominantly of Lg waves in the former and S in the latter. Results indicate that the current conversion relations are not valid for smaller events and need to be reevaluated and provide an improved data set to that end.

Session: Advances in Reliable Earthquake Source Parameter Estimation - I

Type: Oral

Date: 4/16/2025

Presentation Time: 09:00 AM (local time)

Presenting Author: Allison

Student Presenter: No

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