• Login
    About WHOAS
    View Item 
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Geology and Geophysics (G&G)
    • View Item
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Geology and Geophysics (G&G)
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of WHOASCommunities & CollectionsBy Issue DateAuthorsTitlesKeywordsThis CollectionBy Issue DateAuthorsTitlesKeywords

    My Account

    LoginRegister

    Statistics

    View Usage Statistics

    Fine-scale seismic structure of the shallow volcanic crust on the East Pacific Rise at 9°50′N

    Thumbnail
    View/Open
    2004JB003152.pdf (1.378Mb)
    Date
    2004-12-09
    Author
    Sohn, Robert A.  Concept link
    Webb, Spahr C.  Concept link
    Hildebrand, John A.  Concept link
    Metadata
    Show full item record
    Citable URI
    https://hdl.handle.net/1912/3713
    As published
    https://doi.org/10.1029/2004JB003152
    DOI
    10.1029/2004JB003152
    Keyword
     Volcanic; Seismic; Structure 
    Abstract
    We use a combination of body wave and interface wave observations from an on-bottom seismic refraction survey to constrain the fine-scale seismic structure of the upper crust in a ∼3 × 3 km field area centered on the East Pacific Rise at 9°50′N. We detonated 18 explosive shots (18 sources) in a circular pattern (1.5 km radius) on the rise axis and recorded seismic arrivals with eight ocean bottom seismometers (eight receivers). We observed 30–40 Hz compressional body waves from all shots (144 P waves) and 1–3 Hz Stoneley (interface) waves on a subset of source-receiver pairs (58 interface waves). Using a station correction inversion, we find that roughly half of the variance in the P wave first-arrival times results from lateral variations in the thickness of the surface low-velocity layer (SLVL), a layer of extremely porous lava and basalt breccia with an average P wave velocity of 2.2 km s−1. The SLVL thickness increases from <20 m along the axial summit trough (AST) to ∼120 m at near-axis lava depocenters, which are not symmetric about the rise axis. Depocenters are located ∼0.5 km to the west and ∼1.5 km to the east of the rise axis. Tomographic inversion of the Stoneley wave first arrivals reveals that shear velocities in the SLVL covary with the layer thickness, exhibiting a similar asymmetric pattern, with shear velocities increasing from ∼320 m s−1 near the AST to ∼520 m s−1 at the near-axis depocenters. Our analysis demonstrates that the seismic characteristics of the extrusive layer near the rise axis are related primarily to volcanic features and processes. The thickness and velocity of the SLVL are low on the axis and within channel networks that deliver lava flows away from the axis and then increase rapidly at the distal ends of the channels where the lavas are deposited. We find that azimuthal anisotropy exerts only a weak influence on our P wave first-arrival times, which we model as weak (4%) seismic azimuthal anisotropy in the upper dikes with a fast axis oriented N23°–32°W. We find no evidence for seismic azimuthal anisotropy in the extrusive layer.
    Description
    Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): B12104, doi:10.1029/2004JB003152.
    Collections
    • Geology and Geophysics (G&G)
    Suggested Citation
    Journal of Geophysical Research 109 (2004): B12104
     

    Related items

    Showing items related by title, author, creator and subject.

    • Thumbnail

      Seismic structure of the Endeavour Segment, Juan de Fuca Ridge : correlations with seismicity and hydrothermal activity 

      Van Ark, Emily M.; Detrick, Robert S.; Canales, J. Pablo; Carbotte, Suzanne M.; Harding, Alistair J.; Kent, Graham M.; Nedimovic, Mladen R.; Wilcock, William S. D.; Diebold, John B.; Babcock, Jeffrey M. (American Geophysical Union, 2007-02-03)
      Multichannel seismic reflection data collected in July 2002 at the Endeavour Segment, Juan de Fuca Ridge, show a midcrustal reflector underlying all of the known high-temperature hydrothermal vent fields in this area. On ...
    • Thumbnail

      Seismicity and structure of the Orozco transform fault from ocean bottom seismic observations 

      Trehu, Anne M. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1982-02)
      In this thesis, seismic waves generated by sources ranging from 2.7 kg shots of TNT to magnitude 5 earthquakes are studied in order to determine the seismic activity and crustal structure of the Orozco transform fault. ...
    • Thumbnail

      Crustal structure across the Costa Rican Volcanic Arc 

      Hayes, Jorden L.; Holbrook, W. Steven; Lizarralde, Daniel; Van Avendonk, Harm J. A.; Bullock, Andrew D.; Mora, Mauricio M.; Harder, Steven H.; Alvarado, Guillermo E.; Ramirez, Carlos J. (John Wiley & Sons, 2013-04-29)
      Island arcs are proposed to be essential building blocks for the crustal growth of continents; however, island arcs and continents are fundamentally different in bulk composition: mafic and felsic, respectively. The substrate ...
    All Items in WHOAS are protected by original copyright, with all rights reserved, unless otherwise indicated. WHOAS also supports the use of the Creative Commons licenses for original content.
    A service of the MBLWHOI Library | About WHOAS
    Contact Us | Send Feedback | Privacy Policy
    Core Trust Logo