Earthquake-cycle Deformation on Northern Vancouver Island and Haida Gwaii
Abstract
Along the western margin of the North America off northern Vancouver Island and the islands of Haida Gwaii there is a complex triple junction transition zone, between the subducting Juan de Fuca plate system to the south and the transcurrent Queen Charlotte Fault to the north. Here we present crustal deformation data for northern Vancouver Island and Haida Gwaii, determined from continuous and campaign GNSS measurements collected before and after the 2012 M7.8 great thrust earthquake. To the south of Haida Gwaii, there are three oceanic plates or blocks with progressively slower convergence to the north and different convergence directions, the main Juan de Fuca Plate, the Explorer Plate and the Winona Block. GNSS vectors indicate slower Explorer plate subduction compared to the Juan de Fuca plate, and, off northernmost Vancouver Island, the small Winona Block may be converging at an even slower rate. Off Haida Gwaii, oblique convergence appears to be accommodated by the combination of strike-slip motion on the transcurrent Queen Charlotte fault just offshore, and the Haida Gwaii thrust that extends further offshore. On the coastal region prior to the 2012 Haida Gwaii Mw 7.8 great thrust earthquake, we find a northwestward margin-parallel translation extending from northern Vancouver Island into southern Alaska. The origin of the northward translation is poorly understood; there is no geological evidence of shear faulting or related seismicity. The coastal shear cannot reflect interseismic locking on the Queen Charlotte transcurrent fault just offshore, as shown by dislocation modeling, and that the shear extends well south of the Queen Charlotte fault extent. On Haida Gwaii, oblique convergence is apparent in the GPS data, consistent with partitioning between margin-parallel and margin-perpendicular strain on the two faults. From dislocation models there is a high degree of locking on the southernmost of the Queen Charlotte fault. GNSS data after the 2012 Haida Gwaii thrust earthquake show a complex deformation pattern. Sites near the Queen Charlotte fault show a component of strike-slip movement consistent with a creeping transcurrent fault shortly after the earthquake, whereas far-field GNSS sites exhibit widespread post-seismic deformation following the 2012 thrust earthquake.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.G23C0623J
- Keywords:
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- 1209 Tectonic deformation;
- GEODESY AND GRAVITYDE: 3040 Plate tectonics;
- MARINE GEOLOGY AND GEOPHYSICSDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8107 Continental neotectonics;
- TECTONOPHYSICS