Seismic Rupture on an Oceanic-Continental Plate Boundary: Strike-Slip Earthquakes along the Queen Charlotte-Fairweather Fault

摘要

We investigate the 2013 M-w 7.5 Craig, Alaska, earthquake and nearby seismicity to understand better how temperature and composition may control the depth of seismic rupture along a strike-slip fault offsetting contrasting lithosphere types. The Queen Charlotte-Fairweather (QCF) fault lies between the oceanic lithosphere of the Pacific plate and the accreted Insular superterrane of the North American continent. We use point-source and finite-fault modeling of teleseismic body waves to characterize the focal mechanism and the depth extent of seismic rupture of five M-w 5.9-7.5 earthquakes. Four of the five earthquakes are consistent with rupture on the QCF fault. We find that these four earthquakes have centroid depths between 11 and 18 km (+/- 3 km) and aftershocks with an order of magnitude less than typical continental earthquakes. Finite-fault modeling of the 2013 Craig earthquake favors bilateral rupture along a 150 km fault with a depth range of slip between 5 and 25 km, with faster rupture (4-5 km/s) to the north than the south (1 km/s). These results suggest that the transition of brittle to ductile deformation along this section of the Pacific-North American plate boundary is thermally controlled by a more mafic rheology than average continental crust, exhibiting behavior consistent with that of an oceanic strike-slip fault.