The October 28, 2012 M_w 7.8 Haida Gwaii underthrusting earthquake and tsunami: Slip partitioning along the Queen Charlotte Fault transpressional plate boundary
Abstract
The Pacific/North American plate boundary is undergoing predominantly right-lateral strike–slip motion along the Queen Charlotte and Fairweather transform faults. The Queen Charlotte Fault (QCF) hosted the largest historical earthquake in Canada, the 1949 M_S 8.1 strike–slip earthquake, which ruptured from offshore northern Haida Gwaii several hundred kilometers northwestward. On January 5, 2013 an M_w 7.5 strike–slip faulting event occurred near the northern end of the 1949 rupture zone. Along central and southern Haida Gwaii the relative plate motion has ∼20% oblique convergence across the left-stepping plate boundary. There had been uncertainty in how the compressional component of plate motion is accommodated. The October 28, 2012 M_w 7.8 Haida Gwaii earthquake involved slightly (∼20°) oblique thrust faulting on a shallow (∼18.5°) northeast-dipping fault plane with strike (∼320°) parallel to the QCF, consistent with prior inferences of Pacific Plate underthrusting beneath Haida Gwaii. The rupture extended to shallow depth offshore of Moresby Island beneath a 25–30 km wide terrace of sediments that has accumulated in a wedge seaward of the QCF. The shallow thrusting caused seafloor uplift that generated substantial localized tsunami run-up and a modest far-field tsunami that spread across the northern Pacific, prompting a tsunami warning, beach closure, and coastal evacuation in Hawaii, although ultimately tide gauges showed less than 0.8 m of water level increase. The mainshock rupture appears to have spread with a ∼2.3 km/s rupture velocity over a length of ∼150 km, with slip averaging 3.3 m concentrated beneath the sedimentary wedge. The event was followed by a substantial aftershock sequence, in which almost all of the larger events involve distributed intraplate normal faulting extending ∼50 km oceanward from the QCF. The highly oblique slip partitioning in southern Haida Gwaii is distinctive in that the local plate boundary-parallel motion on the QCF may be accommodated either by infrequent large strike–slip ruptures or by aseismic creep, as seems to be the case for deeper oblique relative plate motion beneath Haida Gwaii, while the sedimentary terrace accumulates plate boundary-perpendicular compressional strain that releases in almost pure thrust faulting earthquakes, seaward of the QCF.
Additional Information
© 2013 Elsevier B.V. Received 13 March 2013. Received in revised form 26 April 2013. Accepted 1 May 2013. Editor: P.Shearer. Available online 12 June 2013. We thank Roy Hyndman for comments on the manuscript. This work made use of GMT, SAC, Coulomb 3.0 and Matlab software. The IRIS DMS data center was used to access the seismic data from Global Seismic Network and Federation of Digital Seismic Network stations. DART buoy data were obtained from the NOAA National Data Buoy Center. W. H. K. Lee participated in the analysis of historic seismic records for the 1949 event. This work was supported by NSF grants EAR-1245717 (T.L.).Attached Files
Supplemental Material - mmc1.pdf
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Additional details
- Eprint ID
- 42047
- DOI
- 10.1016/j.epsl.2013.05.005
- Resolver ID
- CaltechAUTHORS:20131024-103237860
- EAR-1245717
- NSF
- Created
-
2013-10-24Created from EPrint's datestamp field
- Updated
-
2021-11-10Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences