An earthquake history derived from stratigraphic and microfossil evidence of relative sea-level change at Coos Bay, southern coastal Oregon (1996)

Research Article| February 01, 1996 An earthquake history derived from stratigraphic and microfossil evidence of relative sea-level change at Coos Bay, southern coastal Oregon Alan R. Nelson; Alan R. Nelson 1U.S. Geological Survey, M.S. 966, P.O. Box 25046, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Anne E. Jennings; Anne E. Jennings 2Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309 Search for other works by this author on: GSW Google Scholar Kaoru Kashima Kaoru Kashima 3Department of Earth and Planetary Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka 810, Japan Search for other works by this author on: GSW Google Scholar GSA Bulletin (1996) 108 (2): 141–154. https://doi.org/10.1130/0016-7606(1996)108<0141:AEHDFS>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alan R. Nelson, Anne E. Jennings, Kaoru Kashima; An earthquake history derived from stratigraphic and microfossil evidence of relative sea-level change at Coos Bay, southern coastal Oregon. GSA Bulletin 1996;; 108 (2): 141–154. doi: https://doi.org/10.1130/0016-7606(1996)108<0141:AEHDFS>2.3.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract Much of the uncertainty in determining the number and magnitude of past great earthquakes in the Cascadia subduction zone of western North America stems from difficulties in using estuarine stratigraphy to infer the size and rate of late Holocene relative sea-level changes. A sequence of interbedded peaty and muddy intertidal sediment beneath a small, protected tidal marsh in a narrow inlet of Coos Bay, Oregon, records ten rapid to instantaneous rises in relative sea level. Each rise is marked by a contact that records an upward transition from peaty to muddy sediment. But only two contacts, dating from about 1700 and 2300 yr ago, show the site-wide extent and abrupt changes in lithology and foraminiferal and diatom assemblages that can be used to infer at least half a meter of sudden coseismic subsidence. Although the characteristics of a third, gradual contact do not differ from those of some contacts produced by nonseismic processes, regional correlation with other similar sequences and high-precision 14C dating suggest that the third contact records a great plate-boundary earthquake about 300 yr ago. A fourth contact formed too slowly to have been caused by coseismic subsidence. Because lithologic and microfossil data are not sufficient to distinguish a coseismic from a nonseismic origin for the other six peat-mud contacts, we cannot determine earthquake recurrence intervals at this site. Similar uncertainties in great earthquake recurrence and magnitude prevail at similar sites elsewhere in the Cascadia subduction zone, except those with sequences showing changes in fossils indicative of >1 m of sudden subsidence, sand sheets deposited by tsunamis, or liquefaction features. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.