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  • Wiley  (3)
  • Seismological Society of America (SSA)  (1)
  • 1
    Publication Date: 2019
    Description: Abstract Deep sedimentary basins amplify long‐period shaking from seismic waves, increasing the seismic hazard for cities sited on such basins. We perform 3‐D simulations of point source earthquakes distributed around the Seattle and Tacoma basins in Washington State to examine the dependence of basin amplification on source azimuth, depth, and earthquake type. For periods between 1 and 10 s, the pattern of amplification is spatially heterogeneous and differs considerably with the source‐to‐site azimuth. For close‐in earthquakes, the greatest basin amplification occurs toward the farside of the basin and ground motions from crustal earthquakes experience greater amplification than those from more vertically incident, deeper intraplate earthquakes. Love and Rayleigh waves form similar spatial patterns for a given source location, although the magnitude of amplification varies. The source dependence of basin amplification is an important factor for seismic hazard assessment, in both the Seattle and Tacoma basins, and by extension for deep sedimentary basins worldwide.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2013-06-11
    Description: [1]  The Grizzly Valley fault system (GVFS) strikes northwestward across Sierra Valley, a low-relief basin situated within a network of active dextral-slip faults in the northern Walker Lane, California. Quaternary motion along the Grizzly Valley fault system has not been previously documented. We used high-resolution (0.25 m) airborne LiDAR data in combination with high-resolution, P-wave, seismic-reflection imaging to evaluate Quaternary deformation associated with the GVFS. We identified suspected tectonic lineaments using the LiDAR data and collected seismic-reflection data along six profiles across the lineaments. The seismic-reflection images reveal a deformed basal marker that we interpret to be the top of Tertiary volcanic rocks overlain by a 120- to 450-m-thick suite of subhorizontal reflectors that we interpret to be Plio-Pleistocene lacustrine deposits. Three profiles image features that we interpret to be the principle active trace of the GVFS, which is a steeply dipping fault zone that vertically offsets the volcanic rocks and the lacustrine basin fill. These data suggest that the GVFS may have been active in latest Quaternary time because: 1) the LiDAR data show subtle surficial geomorphic features that are typical of youthful faulting, including a topographic lineament marked by a ~1-m-high ridge composed of discontinuous, left-stepping lobes; and 2) the seismic profiles demonstrate shallow faulting of the lacustrine strata that coincides with the left-stepping ridge. This investigation illustrates the potential for unidentified, low rate, strike-slip faults in transtensional basins and emphasizes the value of high-resolution topographic data and subsurface imaging as a means of identifying these structures.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2017-09-13
    Description: The Yakima folds of central Washington, USA are prominent anticlines that are the primary tectonic features of the backarc of the northern Cascadia subduction zone. What accounts for their topographic expression and how much strain do they accommodate and over what time period? We investigate Manastash anticline, a north-vergent fault propagation fold typical of structures in the fold province. From retrodeformation of line- and area-balanced cross sections, the crust has horizontally shortened by 11% (0.8-0.9 km). The fold, and by inference all other folds in the fold province, formed no earlier than 15.6 Ma as they developed on a landscape that was reset to negligible relief following voluminous outpouring of Grande Ronde Basalt. Deformation is accommodated on two fault sets including west-northwest-striking frontal thrust faults and shorter north- to northeast-striking faults. The frontal thrust fault system is active with late Quaternary scarps at the base of the range front. The fault-cored Manastash anticline terminates to the east at the Naneum anticline and fault; activity on the north-trending Naneum structures predates emplacement of the Grande Ronde Basalt. The west-trending Yakima folds and west-striking thrust faults, the shorter north to northeast striking faults, and the Naneum fault together constitute the tectonic structures that accommodate deformation in the low-strain-rate environment in the backarc of the Cascadia Subduction Zone.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2012-04-01
    Description: We conducted active and passive seismic imaging investigations along a 5.6-km-long, east–west transect ending at the mapped trace of the Wasatch fault in southern Utah Valley. Using two-dimensional (2D) P-wave seismic reflection data, we imaged basin deformation and faulting to a depth of 1.4 km and developed a detailed interval velocity model for prestack depth migration and 2D ground-motion simulations. Passive-source microtremor data acquired at two sites along the seismic reflection transect resolve S-wave velocities of approximately 200??m/s at the surface to about 900??m/s at 160 m depth and confirm a substantial thickening of low-velocity material westward into the valley. From the P-wave reflection profile, we interpret shallow (100–600 m) bedrock deformation extending from the surface trace of the Wasatch fault to roughly 1.5 km west into the valley. The bedrock deformation is caused by multiple interpreted fault splays displacing fault blocks downward to the west of the range front. Further west in the valley, the P-wave data reveal subhorizontal horizons from approximately 90 to 900 m depth that vary in thickness and whose dip increases with depth eastward toward the Wasatch fault. Another inferred fault about 4 km west of the mapped Wasatch fault displaces horizons within the valley to as shallow as 100 m depth. The overall deformational pattern imaged in our data is consistent with the Wasatch fault migrating eastward through time and with the abandonment of earlier synextensional faults, as part of the evolution of an inferred 20-km-wide half-graben structure within Utah Valley. Finite-difference 2D modeling suggests the imaged subsurface basin geometry can cause fourfold variation in peak ground velocity over distances of 300 m.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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