Low-Frequency Earthquakes on the Queen Charlotte Plate Boundary

English Abstract:

The Queen Charlotte Fault is a major plate boundary located off the northwest coast of North America that has produced large earthquakes in 1949 (M8.1) and more recently in October, 2012 (M7.8). The 2012 event was dominated by thrusting despite the fact that plate motions at the boundary are more nearly transcurrent. We have identified seismic tremor in the region of the Queen Charlotte plate boundary below Haida Gwaii within the frequency band 3 to 12 Hz. The Queen Charlotte Fault region is typified by intermittent tremor activity every few days, which is similar to the San Andreas Fault and in contrast to subduction zones where distinctly episodic tremor and slip is observed. The tremor includes low-frequency earthquakes (LFEs) that are of particular interest due to their relatively high signal-to-noise ratios compared with other areas of investigation such as the northern Cascadia subduction zone, and their distinct phase arrivals. We are currently assembling LFE detection catalogues and templates with two main goals in mind. First, we wish to determine whether LFEs occur predominantly on a shallow crustal transform (i.e., analogous to the San Andreas Fault), a deeper thrust fault (i.e., analogous to the Cascadia subduction zone), or a combination of the two. This information will indicate which portions of the plate boundary system undergo slow slip. Secondly, we will compare LFE activity before and after the 2012 M7.8 earthquake to investigate the influence of the earthquake on fault frictional properties and the stress field.