Imaging the Locked Zone of the Cascadia Subduction Zone Using Receiver Functions from the Cascadia Initiative
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Receiver function
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Abstract We present seafloor pressure records from the Cascadia Subduction Zone, alongside oceanographic and geophysical models, to evaluate the spatial uniformity of bottom pressure and optimize the geometry of sensor networks for resolving offshore slow‐slip transients. Seafloor pressure records from 2011 to 2015 show that signal amplitudes are depth‐dependent, with tidally filtered and detrended root‐mean‐squares of <2 cm on the abyssal plain and >6 cm on the continental shelf. This is consistent with bottom pressure predictions from circulation models and comparable to deformation amplitudes from offshore slow slip observed in other subduction zones. We show that the oceanographic component of seafloor pressure can be reduced to ≤1‐cm root‐mean‐square by differencing against a reference record from a similar depth, under restrictions that vary with depth. Instruments at 100–250 m require depths matched within 10 m at separations of <100 km, while locations deeper than 1,400 m are broadly comparable over separations of at least 300 km. Despite the significant noise reduction from this method, no slow slip was identified in the dataset, possibly due to poor spatiotemporal instrument coverage, nonideal deployment geometry, and limited depth‐matched instruments. We use forward predictions of deformation from elastic half‐space models and hindcast pressure from circulation models to generate synthetic slow‐slip observational records and show that a range of slip scenarios produce resolvable signals under depth‐matched differencing. For future detection of offshore slow slip in Cascadia, we recommend a geometry in which instruments are deployed along isobaths to optimize corrections for oceanographic signals.
Seafloor Spreading
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Abstract Within the fore‐arc of the Cascadia Subduction Zone, there are significant along‐strike differences in the orientation of splay faults, sediment consolidation, and fault roughness. Here, we use dynamic rupture simulations of megathrust earthquakes on different realizations of a fault system that incorporate fore‐arc properties representative of offshore Oregon and Washington to estimate how splay faults may behave in future megathrust earthquakes in Cascadia. While splay faults were activated in all of our simulations, splay orientation is a primary control on slip amplitude. Seaward vergent faults accommodate significant amounts of slip resulting in large seafloor uplift and significantly larger tsunami amplitudes. For example, our median tsunami heights including splay faults are about a factor of two larger than those that did not include splay fault deformation. We suggest that there is an urgent need to revisit existing approaches to tsunami hazard assessment in Cascadia to include the influence of splay faults.
Seafloor Spreading
Tsunami earthquake
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Research Article| October 02, 2017 Influence of the megathrust earthquake cycle on upper-plate deformation in the Cascadia forearc of Washington State, USA Jaime E. Delano; Jaime E. Delano * 1Department of Geology, Western Washington University, 516 High Street, Bellingham, Washington 98225, USA *Current address: U.S. Geological Survey, Geologic Hazards Science Center, 1711 Illinois Street, Golden, Colorado 80401, USA; E-mail: jdelano@usgs.gov. Search for other works by this author on: GSW Google Scholar Colin B. Amos; Colin B. Amos 1Department of Geology, Western Washington University, 516 High Street, Bellingham, Washington 98225, USA Search for other works by this author on: GSW Google Scholar John P. Loveless; John P. Loveless 2Department of Geosciences, Smith College, 44 College Lane, Northampton, Massachusetts 01063, USA Search for other works by this author on: GSW Google Scholar Tammy M. Rittenour; Tammy M. Rittenour 3Department of Geology, Utah State University, 4505 Old Main Hill, Logan, Utah 84322, USA Search for other works by this author on: GSW Google Scholar Brian L. Sherrod; Brian L. Sherrod 4U.S. Geological Survey, Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Emerson M. Lynch Emerson M. Lynch 2Department of Geosciences, Smith College, 44 College Lane, Northampton, Massachusetts 01063, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Jaime E. Delano * 1Department of Geology, Western Washington University, 516 High Street, Bellingham, Washington 98225, USA Colin B. Amos 1Department of Geology, Western Washington University, 516 High Street, Bellingham, Washington 98225, USA John P. Loveless 2Department of Geosciences, Smith College, 44 College Lane, Northampton, Massachusetts 01063, USA Tammy M. Rittenour 3Department of Geology, Utah State University, 4505 Old Main Hill, Logan, Utah 84322, USA Brian L. Sherrod 4U.S. Geological Survey, Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, Washington 98195, USA Emerson M. Lynch 2Department of Geosciences, Smith College, 44 College Lane, Northampton, Massachusetts 01063, USA *Current address: U.S. Geological Survey, Geologic Hazards Science Center, 1711 Illinois Street, Golden, Colorado 80401, USA; E-mail: jdelano@usgs.gov. Publisher: Geological Society of America Received: 16 Feb 2017 Revision Received: 13 Jul 2017 Accepted: 13 Jul 2017 First Online: 02 Oct 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2017 Geological Society of America Geology (2017) 45 (11): 1051–1054. https://doi.org/10.1130/G39070.1 Article history Received: 16 Feb 2017 Revision Received: 13 Jul 2017 Accepted: 13 Jul 2017 First Online: 02 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jaime E. Delano, Colin B. Amos, John P. Loveless, Tammy M. Rittenour, Brian L. Sherrod, Emerson M. Lynch; Influence of the megathrust earthquake cycle on upper-plate deformation in the Cascadia forearc of Washington State, USA. Geology 2017;; 45 (11): 1051–1054. doi: https://doi.org/10.1130/G39070.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The influence of subduction zone earthquake cycle processes on permanent forearc deformation is poorly understood. In the Cascadia subduction zone forearc of Washington State, USA, deformed and incised fluvial terraces serve as archives of longer-term (103–104 yr) strain manifest as both fluvial incision and slip on upper-plate faults. We focus on comparing these geomorphic records in the Wynoochee River valley in the southern Olympic Mountains with short-term (101 yr) deformation driven by interseismic subduction zone coupling. We use optically stimulated luminescence dating and high-resolution elevation data to characterize strath terrace incision and differential uplift across the Canyon River fault, which cuts Wynoochee River terraces. This analysis demonstrates reverse slip rates of ∼0.1–0.3 mm/yr over the past ∼12–37 k.y., which agree with rates predicted by a GPS-constrained boundary element model of interseismic stress from Cascadia subduction zone coupling. Similarly, model-predicted patterns of interseismic uplift mimic the overall pattern of incision in the lower Wynoochee River valley, as revealed by strath elevations dated at 14.1 ± 1.2 ka. Agreement between modeled short-term and observed long-term records of forearc strain suggests that interseismic stress drives slip on upper-plate faults and fluvial incision in Cascadia. Consistency over multiple time scales may indicate relative stability in spatial patterns of subduction zone coupling over at least ∼104 yr intervals. 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Forearc
Geological survey
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Component (thermodynamics)
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Forearc
Wedge (geometry)
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