Implications of 5+ years of post-seismic crustal deformation following the Mw7.8 October 28, 2012 Haida Gwaii and Mw7.5 January 5, 2013 Craig, AK earthquakes along the Queen Charlotte-Fairweather fault system
Abstract
The Queen Charlotte—Fairweather Fault System (QC-FF), runs along the western coast of British Columbia, Canada, and southeast Alaska, USA and accommodates about 50 mm/yr dextral plate boundary motion between the Pacific and North America plates. It separates warm oceanic crust to the west, from former back-arc and continental craton to the east, and it has been active for the last 43 Ma. Ten ≥M6.7 earthquakes have occurred along its length since 1910, with the largest event reaching M8.1, in 1949. The two most recent M≥7.5 earthquakes along the QC-FF, the Mw7.8 October 28, 2012 Haida-Gwaii earthquake and Mw 7.5 January 5, 2013 Craig, AK earthquake, were observed by continuous Global Position System (CGPS) stations in both Alaska and British Columbia. We utilize 5+ years of GPS time series from 25 CGPS stations to analyze the post-seismic transient produced by these events in order to (1) characterize the mechanisms of postseismic deformation and (2) better constrain the viscosity structure of the crust and upper mantle surrounding the QC-FF plate boundary fault. We constructed a 2D model of viscoelastic structure, varying with depth and distance normal to the QC-FF, with variable transient and steady-state viscosity under the former backarc region. Finite source models of the two earthquakes are available from previous seismic waveform analysis and were validated against observed static offsets. Using these source models, joint viscoelastic relaxation and afterslip models were constructed by evaluating the fit of the data to a 2.5D forward model of viscoelastic relaxation for a large set of candidate models of transient and steady-state viscosities. Then for each model we fit residuals with least-squares inversion for afterslip parameters from the Haida-Gwaii event. Preliminary results indicate temporally-decaying afterslip with an exponential constant 1 year and vigorous viscoelastic relaxation of the mantle asthenosphere. In addition, our best-fit viscosity structure (transient viscosity of 1018 Pa s; steady-state viscosity of 1019 Pa s) is consistent with the range of crustal and upper mantle viscosities determined in previous studies of glacial isostatic rebound measurements.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.G23B0590G
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 1211 Non-tectonic deformation;
- GEODESY AND GRAVITYDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS