skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Incipient Subduction and Slip Partitioning at High Obliquity: The Haida Gwaii Plate Boundary
Abstract Plate motion obliquity along the dominantly transform Queen Charlotte plate boundary (QCPB) peaks offshore Haida Gwaii. To investigate the effects of obliquity on plate boundary deformation, we analyze continuous seismic waveforms from temporary and permanent stations from 1998 to 2020 to generate a catalog of ∼50,000 earthquakes across Haida Gwaii. We use an automated technique based on auto‐regressive phase detection and onset estimation to obtain the initial seismic catalog, integrate existing catalogs, invert for 3D velocity structure using data from the best constrained period, and relocate the entire catalog using the new 3D velocity model. We investigate the seismically active sections of the transcurrent Queen Charlotte fault (QCF), noting that little seismicity locates directly along its bathymetrically defined trace. Instead, seismicity illuminates a complex system of segmented structures with variable geometries along strike. Other clusters highlight active shallow faults within the highly deformed Queen Charlotte terrace. Few aftershocks appear on the thrust plane of the 2012Mw7.8 Haida Gwaii earthquake except near its inferred intersection with the QCF at 15–20 km depths, suggesting elevated residual stress at the juncture of slip‐partitioning. Deep crustal seismicity (up to ∼20 km depths) beneath central Haida Gwaii aligned parallel to the strike of the thrust plane may represent landward underthrusting of the Pacific plate. Our results suggest possible coseismic strike‐slip rupture on the QCF during the 2012 earthquake and add support to the thesis that highly oblique transform boundaries are viable settings for subduction initiation.  more » « less
Award ID(s):
2128783 1824927
PAR ID:
10539411
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
AGU
Date Published:
Journal Name:
Journal of Geophysical Research: Solid Earth
Volume:
129
Issue:
5
ISSN:
2169-9313
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Science Advances)
    The Queen Charlotte plate boundary (QCPB), a transform separating the Pacific and North American plates, accommodates ~55 millimeters per year of motion, is a source of large earthquakes in the northeast Pacific, and may be a modern site of subduction initiation. The southern QCPB experiences oblique convergence, showcased by the 1949 magnitude (M) 8.1 strike-slip earthquake and the 2012M7.8 tsunamigenic thrust earthquake, both offshore Haida Gwaii, British Columbia. We present seismic reflection images of the southern QCPB, which constrain the crustal structure in unprecedented detail. The Queen Charlotte Terrace is underthrust by oceanic crust topped by a throughgoing, low-angle plate-boundary thrust, which ruptured in the 2012 earthquake. The Queen Charlotte Terrace is analogous to strain-partitioned, thin-skinned forearc slivers seen at oblique subduction zones, captured between a localized plate-boundary thrust and a mature strike-slip fault. Our imaging suggests that the system rapidly evolved from distributed to partitioned strain and is currently an incipient subduction zone. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; (, Seismological Research Letters)
    Abstract Plate boundaries in the oceans are often poorly monitored. Though typically less remote than the deep sea, shallow marine environments with seafloor depths <0.5 km can be especially challenging for seismic experiments due to natural and anthropogenic hazards and noise sources that can affect instrument survival and data quality. The Queen Charlotte fault (QCF) is part of a transform plate boundary that follows the continental shelf of the Alaska Panhandle and central British Columbia. This fault system accommodates dextral slip between the Pacific and North American plates and has hosted several historic Mw > 7 earthquakes. In August 2021, we deployed 28 broadband ocean-bottom seismometers (OBSs) along the central QCF for the “Transform Obliquity along the Queen Charlotte Fault and Earthquake Study” (TOQUES) to investigate fault architecture and local seismicity. Deployment depths varied between 0.2 and 2.5 km below sea level, with half of the instruments deployed in shallow water (<0.5 km depth). We describe the scientific motivations for the TOQUES broadband OBS array, present data metrics, and discuss factors that influence data quality and instrument survival. We show that many opportunities exist for scientific study of shallow marine environments and the solid earth. Despite concerns that shallow water was responsible for the risk of data or instrument loss, direct relationships between instrument success and water depth are inconclusive. Rather, instrument success may be more related to the ability of different instrument designs to withstand shallow-water conditions. 
    more » « less
  3. (, Seismological Research Letters)
    Abstract I present a high-precision earthquake relocation catalog and first-motion focal mechanisms before and during the 2019 Ridgecrest earthquake sequence in eastern California. I obtain phase arrivals, first-motion polarities, and waveform data from the Southern California Earthquake Data Center for more than 24,000 earthquakes with the magnitudes varying between −0.7 and 7.1 from 1 January to 31 July 2019. I first relocate all the earthquakes using phase arrivals through a previously developed 3D seismic-velocity model and then improve relative location accuracies using differential times from waveform cross correlation. The majority of the relocated seismicity is distributed above 12 km depth. The seismicity migration along the northwest–southeast direction can be clearly seen with an aseismic zone near the Coso volcanic field. Focal mechanisms are solved for all the relocated events based on the first-motion polarity data with dominant strike-slip fault solutions. The Mw 6.4 and 7.1 earthquakes are positioned at 12.45 and 4.16 km depths after the 3D relocation, respectively, with strike-slip focal solutions. These results can help our understanding of the 2019 Ridgecrest earthquake sequence and can be used in other seismological and geophysical studies. 
    more » « less
  4. ; ; ; ; (, Seismological Research Letters)
    Abstract The Alaska Peninsula section of the Alaska-Aleutian subduction zone shows significant along-strike variations in seismic activity and interseismic plate coupling. This region experienced the 2020 Mw 7.8 Simeonof megathrust, Mw 7.6 Sand Point strike-slip, and 2021 Mw 8.2 Chignik megathrust earthquakes. This study, utilizing deep learning techniques, presents a high-precision earthquake catalog, providing insights into background seismicity, aftershocks, and slab geometry. An abrupt change in the slab dip angle at 30–40 km depths in the Shumagin segment acted as a barrier to the Simeonof and Sand Point earthquake ruptures. The Simeonof event triggered more aftershocks in the overriding plate than the Chignik event, suggesting the overriding plate is more deformed and hydrated in the Shumagin segment. The Sand Point earthquake triggered numerous aftershocks in the overriding plate, delineating a fault in the overriding plate with similar geometry as the intraslab mainshock fault, but activated around seven days after the mainshock. 
    more » « less
  5. ; ; ; (, Journal of Geophysical Research: Solid Earth)
    Abstract The Queen Charlotte‐Fairweather Fault (QC‐FF) system off the coast of British Columbia and southeast Alaska is a highly active dextral strike‐slip plate boundary that accommodates ∼50 mm/yr of relative motion between the Pacific and North America plates. NineMW ≥ 6.7 earthquakes have occurred along the QC‐FF system since 1910, including aMS(G‐R)8.1 event in 1949. Two recent earthquakes, the October 28, 2012 Haida Gwaii (MW7.8) and January 5, 2013 Craig, Alaska (MW7.5) events, produced postseismic transient deformation that was recorded in the motions of 25 nearby continuous Global Positioning System (cGPS) stations. Here, we use 5+ yr of cGPS measurements to characterize the underlying mechanisms of postseismic deformation and to constrain the viscosity structure of the upper mantle surrounding the QC‐FF. We construct forward models of viscoelastic deformation driven by coseismic stress changes from these two earthquakes and explore a large set of laterally heterogeneous viscosity structures that incorporate a relatively weak back‐arc domain; we then evaluate each model based on its fit to the postseismic signals in our cGPS data. In determining best‐fit model structures, we additionally incorporate the effects of afterslip following the 2012 event. Our results indicate the occurrence of a combination of temporally decaying afterslip and vigorous viscoelastic relaxation of the mantle asthenosphere. In addition, our best‐fit viscosity structure (transient viscosity of 1.4–2.0 × 1018 Pa s; steady‐state viscosity of 1019 Pa s) is consistent with the range of upper mantle viscosities determined in previous studies of glacial isostatic rebound and postseismic deformation. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email