Subaqueous Tectonic Geomorphology Along the Queen Charlotte Fault: Evidence for Plate Boundary Localization Based on Slip-Rate Estimates For The Last 17,000 years
Abstract
Seismic and geodetic monitoring of active fault systems does not typically extend beyond one seismic cycle, hence it is challenging to link the characteristics of individual earthquakes with long-term fault behavior, particularly for faults located offshore. The Queen Charlotte Fault (QCF) is a dextral strike-slip fault that carries virtually all of the relative motion along the North America-Pacific plate boundary for 900 km offshore southeastern Alaska and western British Columbia. Although the QCF has generated seven Mw>7 earthquakes since 1900, its kinematics and long-term behavior have never been examined systematically due to an absence of marine geophysical imaging. We present new analysis of the tectonic geomorphology along the entire length of the QCF based on comprehensive multibeam bathymetry data acquired between 2010 and 2018. In the north, from Icy Point to the southern tip of Baranof Island ( 315 km), the fault is a linear and continuous trace that is closely aligned with plate motion vectors. Its strike is increasingly oblique to plate motion moving south and secondary faults and folds along the continental slope become more prevalent, suggesting transpressional deformation increases as the horizontal slip rate decreases. We present a catalog of 150 seabed features (e.g., gullies, canyons, escarpments, rills, ridges, and fan aprons) that have been offset horizontally by motion on the QCF since the late Pleistocene. The offset estimates are based on a quantitative reconstruction approach and range from 680-900 m. All of the features are relic, having formed rapidly during the final stages of deglaciation (17-13 ka) when the low-stand shoreline was proximal to the shelf-edge and outwash-derived sediment flows occurred frequently. Dated sediment cores suggest outwash sediment delivery to the slope shut down abruptly, but the timing varied along the margin. Hence, the horizontal slip-rate on the fault is consistently between 47-54 mm/yr over a distance of >680 km. Despite the apparent increase in transpression along the southern section of the fault, we estimate the rate of convergence to be less than 10 mm/yr. These results have implications for regional tectonic models, historical earthquake behavior, and tsunami generation along the QCF.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP54A..02B
- Keywords:
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- 1105 Quaternary geochronology;
- GEOCHRONOLOGYDE: 1130 Geomorphological geochronology;
- GEOCHRONOLOGYDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS