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

Abstract

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.Online Material: Figures of best-fitting point-source focal mechanism and waveform fits, dip sensitivity, directivity tests, aftershock distributions, and finite-fault results.

Slip Behavior of the Queen Charlotte Plate Boundary Before and After the 2012, MW 7.8 Haida Gwaii Earthquake: Evidence From Repeating Earthquakes

“…For simplicity, we will refer to all times prior to the HGEQ as interseismic, and all times after the HGEQ as postseismic, for both the subduction interface and the QCF. Note that the 2013, M W 7.5 Craig earthquake occurred on the QCF ∼200 km north of our study area (Aderhold & Abercrombie, ; Holtkamp & Ruppert, ), but we do not observe any response to this earthquake and thus do not consider it in our analysis.…”

“…The QCPB has hosted Canada's two largest recorded earthquakes: the 1949, M s 8.1 Queen Charlotte Islands earthquake (Bostwick, 1984;Nishenko & Jacob, 1990;Rogers, 1986), and the 2012, M W 7.8 Haida Gwaii earthquake (Cassidy et al, 2014;Kao et al, 2015;Lay et al, 2013). Farther to the north in Alaska, USA, the plate boundary also spawned the M W 7.5 Craig, Alaska earthquake in 2013 (Aderhold & Abercrombie, 2015;Holtkamp & Ruppert, 2015), as well as other large earthquakes in 1958 (M W 8.2) and 1972 (M s 7.6) (Nishenko & Jacob, 1990). These earthquakes underline the considerable seismic hazard posed by the QCPB.…”

Seismotectonics of a diffuse plate boundary: Observations off the Sumatra‐Andaman trench

“…We consider the earthquake in the Bay of Bengal separately because of the significant differences in local velocity structure. We follow the methods outlined in Aderhold and Abercrombie [], which are based on the work of Maggi et al . [].…”

The 2015 Mw 7.1 earthquake on the Charlie‐Gibbs transform fault: Repeating earthquakes and multimodal slip on a slow oceanic transform

“…We calculate a double‐couple moment tensor for this earthquake following Aderhold and Abercrombie [] and Maggi et al . [].…”

“…We calculate a double-couple moment tensor for this earthquake following Aderhold and Abercrombie [2015] and Maggi et al [2000]. Recorded body waves are obtained from stations at teleseismic distances of 30-90°( Incorporated Research Institutions for Seismology Data Management Center (IRIS DMC)); we rotate the horizontals to obtain the SH component.…”