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Local Earthquake Monitoring of the Central Queen Charlotte Fault With an Ocean-Bottom Seismic Array

Description: 

High-resolution bathymetry data show that most Holocene slip along the central Queen Charlotte Fault (QCF) has occurred along a narrow fault zone near the edge of the North American continental shelf. Local seismicity along the central QCF is poorly determined because the fault is offshore, and the nearest permanent networked seismic station is >70 km away. Yet, this fault can generate large, hazardous earthquakes. From August 2021 to September 2022, we deployed an array of 28 broadband ocean-bottom seismometers (OBS) along the central QCF within the rupture zone of the 2013 Craig earthquake. Winter storms and strong tidal currents generate significant noise that complicates signal detection and characterization on shallowly deployed (<300 m water depth) seafloor instruments, however, 19 of these instruments recorded useful data for locating nearby earthquakes. We use these stations and 8 networked seismometers to produce an earthquake catalog, using a deep-neural network-based picking routine. Our preliminary earthquake catalog (~1300 earthquakes) shows strong seasonal variation in the number of events. This seasonality may be due to strong secondary microseism noise from winter storms (0.1-3 Hz) and fin whale calls (15-30 Hz) that are more frequent in winter months; both mask portions of the local earthquake spectrum. Most earthquakes are found <10 km from the Queen Charlotte Fault, confirming that most modern tectonic deformation is in a narrow fault zone that dips gently to the northeast. Preliminary locations show a degree of vertical clustering and most earthquakes are in the mid- and lower-crust (~5-20 km). These results suggest that the central QCF is deforming under simple shear in comparison to more oblique, pure shear deformation to the south. Earthquake depth distributions and the degree of localization represented the new seismicity catalog should provide new insight into the rheological conditions along the ocean-continent plate boundary fault. This dataset is also valuable as a prototype for seismic deployments in shallow-water regions of high wave, winter storm and whale activity.

Session: Structure, Seismicity and Dynamics of the Queen Charlotte-Fairweather Fault System
[Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Andrew

Student Presenter: No

Invited Presentation: 

Authors