Synthesis: Knowns and Unknowns of the Cascadia Subduction Zone II Posters
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Research Article| September 25, 2018 Newly detected earthquakes in the Cascadia subduction zone linked to seamount subduction and deformed upper plate Emily A. Morton; Emily A. Morton 1Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Susan L. Bilek; Susan L. Bilek 1Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Charlotte A. Rowe Charlotte A. Rowe 2Los Alamos National Laboratory, EES-17, MS F-665, P.O. Box 1663, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Geology (2018) 46 (11): 943–946. https://doi.org/10.1130/G45354.1 Article history received: 06 Jul 2018 rev-recd: 31 Aug 2018 accepted: 05 Sep 2018 first online: 25 Sep 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Emily A. Morton, Susan L. Bilek, Charlotte A. Rowe; Newly detected earthquakes in the Cascadia subduction zone linked to seamount subduction and deformed upper plate. Geology 2018;; 46 (11): 943–946. doi: https://doi.org/10.1130/G45354.1 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 Data from an amphibious seismic network in Cascadia (northwest North America) provide unique near-source observations to assess the influence of subducting topography on seismicity. Using subspace detection, we detect and locate 222 events in two separate clusters, near a subducted seamount and a possibly accreted seamount. Seismicity in both clusters is largely shallower than the plate interface and exhibits occasional swarm-like behavior. This implies that the seamount is subducting aseismically via weak coupling with the overriding plate, while earthquakes in the upper plate arise from a high degree of fracturing due to seamount interaction, and the accreted seamount induced similar fracturing before off-scraping. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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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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Abstract Coastal subsidence, dating of plant remains and tree rings, and evidence for tsunami inundation point to coseismic activity on a sizable portion of the Cascadia subduction zone around three centuries ago. A tsunami of remote origin in 1700 C.E., probably from Cascadia, caused flooding and damage in Japan. In previous modeling, this transpacific evidence was found most simply explained by one Cascadia rupture about 1,000 km long. Here I model tens of thousands of ruptures and simulate their subsidence and tsunami signals and show that it is possible that the earthquake was part of a sequence of several events. Partial rupture of ∼400 km offshore southern Oregon and northern California in one large M ≥ 8.7 earthquake can explain the tsunami in Japan without conflicting with the subsidence. As many as four more earthquakes with M ≤ 8.7 can complete the subsidence signal without their tsunamis being large enough to be recorded in Japan. The purpose of this study is not to find a single, most likely, scenario or disprove the single‐rupture hypothesis favored by alternative evidence such as turbidites. Rather, it demonstrates that a multiple rupture sequence may explain part of the available data, and therefore cannot be discounted. Given the gaps in the presently available estimates of subsidence it is also possible that segments of the megathrust, for example from Copalis to the Strait of Juan de Fuca, did not rupture in 1700. The findings have significant implications for Cascadia geodynamics and how earthquake and tsunami hazards in the region are quantified.
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The Cascadia subduction zone (CSZ), where the Juan de Fuca and Gorda plates subduct obliquely beneath North America at a rate of about 35 millimeters per year, poses major geological hazards to population centers of the northwestern United States. Despite the importance of the subducting slab in these hazards, the plate boundary is poorly mapped and understood, especially offshore.
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