Localized shear in the deep lithosphere beneath the San Andreas fault system

Abstract

Research Article| April 01, 2014 Localized shear in the deep lithosphere beneath the San Andreas fault system Heather A. Ford; Heather A. Ford * 1Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, Rhode Island 02912, USA *Current address: Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA; E-mail: heather.ford@yale.edu. Search for other works by this author on: GSW Google Scholar Karen M. Fischer; Karen M. Fischer 1Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, Rhode Island 02912, USA Search for other works by this author on: GSW Google Scholar Vedran Lekic Vedran Lekic 2Department of Geology, University of Maryland, College Park, Maryland 20742, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Heather A. Ford * 1Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, Rhode Island 02912, USA Karen M. Fischer 1Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, Rhode Island 02912, USA Vedran Lekic 2Department of Geology, University of Maryland, College Park, Maryland 20742, USA *Current address: Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA; E-mail: heather.ford@yale.edu. Publisher: Geological Society of America Received: 19 Sep 2013 Revision Received: 31 Dec 2013 Accepted: 10 Jan 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2014 Geological Society of America Geology (2014) 42 (4): 295–298. https://doi.org/10.1130/G35128.1 Article history Received: 19 Sep 2013 Revision Received: 31 Dec 2013 Accepted: 10 Jan 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Heather A. Ford, Karen M. Fischer, Vedran Lekic; Localized shear in the deep lithosphere beneath the San Andreas fault system. Geology 2014;; 42 (4): 295–298. doi: https://doi.org/10.1130/G35128.1 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 Seismic images of the base of the lithosphere across the San Andreas fault system (California, USA) yield new constraints on the distribution of deformation in the deep lithosphere beneath this strike-slip plate boundary. We show that conversions of shear to compressional waves (Sp) across the base of the lithosphere are systematically weaker on the western side of the plate boundary, indicating that the drop in seismic shear-wave velocity from lithosphere to asthenosphere is either smaller or occurs over a larger depth range. In central and northern California, the lithosphere-asthenosphere boundary changes character across a distance of <50 km, and does so directly beneath the San Andreas fault along its simple central segment, and beneath the Calaveras–Green Valley–Bartlett Springs faults to the north. Given the absolute velocities of the North America and Pacific plates, and low viscosities inferred for the asthenosphere, these results indicate the juxtaposition of mantle lithospheres with different properties across these faults. The spatial correlation between the central San Andreas fault and the laterally abrupt change in the velocity structure of the deepest mantle lithosphere points to the accommodation of relative plate motion on a narrow shear zone (<50 km in width), and a rheology that enables strain localization throughout the thickness of the lithosphere. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.