New Constraints on Crustal Structure and Fault Zone Architecture in the m7.8 2012 Haida Gwaii Earthquake Source Region, Offshore British Columbia
Description:
The Queen Charlotte Fault (QCF) transform plate boundary offshore western Canada and southeast Alaska accommodates >50 mm/yr of dextral strike-slip motion between the Pacific (PAC) and North America (NA) plates. Transpressional deformation occurs offshore Haida Gwaii in the southern QCF, generating the Queen Charlotte Terrace fold and thrust belt and a M7.8 thrust type earthquake and tsunami in 2012. Multiple existing hypotheses seek to explain oblique convergence in the southern QCF, ranging from oblique subduction to crustal shortening and buckling as leading end members, but crustal-scale imaging in the region has been limited. In 2021-2022, the Transform Obliquity along the QCF and Earthquake Study (TOQUES) collected active-passive marine seismic data along a ~450 km-long section of the QCF. Here, we focus on long-offset (15-km streamer) multichannel seismic reflection data collected aboard the R/V Marcus G. Langseth that samples the 2012 earthquake epicentral region. We observe extensive crustal-scale normal faulting on the PAC, with vertical offsets up to 500 m at the oceanic Moho and active deformation up to the seafloor, through 2-3 km-thick sediments. These features indicate significant bending of the PAC plate as it enters the deformation zone and are consistent with normal faulting aftershock sequences from the 2012 event. The data show evidence for multiple stages of deformation and reworking within the sediments of the Queen Charlotte Terrace. A narrow region of thrust faulting occurs west of the main QCF trace within a deformed sedimentary section up to ~8 km thick. The main QCF is expressed as a near-vertical structure imaged at up to ~4 km depth. East of the QCF, strata within the upper ~1.5 km are minimally deformed, suggesting that compressional deformation in the shallow terrace is decoupled from the NA backstop. Bright, low-frequency reflectors beneath the sediments of the QCT potentially represent deformed oceanic basement. We suggest that PAC-NA convergence is accommodated via underthrusting and PAC plate deformation with minimal shallow deformation within the NA plate.
Session: Structure, Seismicity and Dynamics of the Queen Charlotte-Fairweather Fault System [Poster Session]
Type: Poster
Date: 5/1/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Lindsay
Student Presenter: No
Invited Presentation:
Authors
Lindsay Worthington Presenting Author Corresponding Author lworthington@unm.edu University of New Mexico |
Collin Brandl cbrandl@unm.edu University of New Mexico |
Emily Roland rolande2@wwu.edu Western Washington University |
Maureen Walton maureen.walton@nrlssc.navy.mil U.S. Naval Research Laboratory |
Mladen Nedimović mladen@dal.ca Dalhousie University |
Andrew Gase gasea@wwu.edu Western Washington University |
Jose Castillo Castellanos js405390@dal.ca Dalhousie University |
Michael Bostock bostock@eoas.ubc.ca University of British Columbia |
Sarah Jaye Oliva soliva@uvic.ca University of Victoria |
Benjamin J Phrampus benjamin.phrampus@nrlssc.navy.mil U.S. Naval Research Laboratory, Stennis, Mississippi, United States |
Olumide Adedeji oadedeji@unm.edu University of New Mexico, Albuquerque, New Mexico, United States |
New Constraints on Crustal Structure and Fault Zone Architecture in the m7.8 2012 Haida Gwaii Earthquake Source Region, Offshore British Columbia
Category
Structure, Seismicity and Dynamics of the Queen Charlotte-Fairweather Fault System