Soft-sediment deformation produced by tides in a meizoseismic area, Turnagain Arm, Alaska

Research Article| May 01, 2007 Soft-sediment deformation produced by tides in a meizoseismic area, Turnagain Arm, Alaska Stephen F. Greb; Stephen F. Greb 1Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky 40506, USA Search for other works by this author on: GSW Google Scholar Allen W. Archer Allen W. Archer 2Department of Geology, Kansas State University, Manhattan, Kansas 66506, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Stephen F. Greb 1Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky 40506, USA Allen W. Archer 2Department of Geology, Kansas State University, Manhattan, Kansas 66506, USA Publisher: Geological Society of America Received: 30 Aug 2006 Revision Received: 22 Dec 2006 Accepted: 28 Dec 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2007) 35 (5): 435–438. https://doi.org/10.1130/G23209A.1 Article history Received: 30 Aug 2006 Revision Received: 22 Dec 2006 Accepted: 28 Dec 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Stephen F. Greb, Allen W. Archer; Soft-sediment deformation produced by tides in a meizoseismic area, Turnagain Arm, Alaska. Geology 2007;; 35 (5): 435–438. doi: https://doi.org/10.1130/G23209A.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 Turnagain Arm is a semidiurnal hypertidal estuary in southeastern Alaska with a recorded tidal range of 9 m. Contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the Mw 9.2 Great Alaskan earthquake of 1964. Horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas. Although many types of soft-sediment deformation structures can be formed by earthquakes, observations of sedimentation on tidal flats in the inner parts of Turnagain Arm in the summers of 2003 and 2004 show that a wide range of soft-sediment deformation structures, similar to those inferred to have been formed by earthquakes, can form in macrotidal estuaries in the absence of seismic shock. During sedimentation rate measurements in 2004, soft-sediment deformation structures were recorded that formed during one day's tide, either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1.8 m tidal bore. Structures consisted of flow rolls, dish structures, flames, and small dewatering pipes in a bed 17 cm thick. In the future, if the flow rolls in Turnagain Arm were found in isolated outcrops across an area 11 km in length, in an estuary known to have been influenced by large-magnitude earthquakes, would they be interpreted as seismites? These examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms (tidal flux, tidal bores, slumping, flooding) that can cause deformation in rapidly deposited, unconsolidated silts and sands, are orders of magnitude more common than great earthquakes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.