| Abstract: | Fossil diatoms from four stratigraphic sections along the tidal Niawiakum River, southwestern Washington, provide an independent paleoecological test of a relative sea-level rise that has been attributed to subsidence during an inferred earthquake in the Cascadia subduction zone about 300 yr ago. Diatom assemblages in a buried soil and overlying mud indicate a sudden and lasting shift from marshes and forests near or above highest tides to mud flats and incipient tidal marshes, with a progressive return to high-level tidal marshes by sediment aggradation and, perhaps, gradual tectonic uplift. The maount of coseismic submergence required to generate the paleoecological changes observed at these sites could have ranged from a minimum of 0.8-1.0m to a maximum of ~3.0m. The following tsunami extended farther landward than was previously inferred from the stratigraphy. These data rule out proposed alternatives to the coseismic subsidence model - that is, climatically induced sea-level rise, temporary submergence caused by storms - and support the hypothesis that a great earthquake struck southwestern Washington 300 yr ago. -from Author |
| Genre: | Article |
| ProdID: | 70019144 |
| Citation Author: | Hemphill-Haley, E. |
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| Citation End Page: | 378 |
| Citation Issue: | 3 |
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| Citation Language: | English |
| Citation Larger Work Title: | Geological Society of America Bulletin |
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| Citation Number Of Pages: | 12 |
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| Citation Search Results Text: | Diatom evidence for earthquake-induced subsidence and tsunami 300 yr ago in southern coastal Washington; 1995; Article; Journal; Geological Society of America Bulletin; Hemphill-Haley, E. |
| Citation Start Page: | 367 |
| Citation Volume: | 107 |
| Citation Year: | 1995 |
| Type: | citation/reference |
| Text: | Diatom evidence for earthquake-induced subsidence and tsunami 300 yr ago in southern coastal Washington; 1995; Article; Journal; Geological Society of America Bulletin; Hemphill-Haley, E. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Sun, 1 Jan 1995 00:00 -0600 |
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