{"id":57483,"date":"2015-08-24T00:00:00","date_gmt":"2015-08-24T00:00:00","guid":{"rendered":"https:\/\/www.uri.edu\/news-draft\/uncategorized\/uri-researcher-geologic-record-of-ancient-earthquakes-and-tsunamis-will-help-understand-future-impacts\/"},"modified":"2015-08-24T00:00:00","modified_gmt":"2015-08-24T00:00:00","slug":"uri-researcher-geologic-record-of-ancient-earthquakes-and-tsunamis-will-help-understand-future-impacts","status":"publish","type":"post","link":"https:\/\/www.uri.edu\/news\/2015\/08\/uri-researcher-geologic-record-of-ancient-earthquakes-and-tsunamis-will-help-understand-future-impacts\/","title":{"rendered":"URI researcher: Geologic record of ancient earthquakes and tsunamis will help understand future impacts"},"content":{"rendered":"
\n\t\tSea level history vital to estimating earthquake, tsunami history<\/p>\n

KINGSTON, R.I. \u2013 August 24, 2015 \u2013 The devastating 2004 Indian Ocean earthquake and tsunami that killed 230,000 people has raised questions among coastal residents about when the next big tsunami will strike. It\u2019s a question that University of Rhode Island geologist Simon Engelhart knows cannot be answered with any precision. <\/p>\n


\nBut he and colleagues from Humboldt State University, Rutgers University and the Earth Observatory of Singapore, in collaboration with geologists from Indonesia, examined the geological record in northern Sumatra to better understand how frequently large earthquakes and tsunamis occur there. The research was published in the August edition of the journal Geology.<\/p>\n


\n\tWhat they found was evidence that five to seven major tsunamis had occurred between 7,400 and 3,800 years ago, with an additional four to six tsunamis since that time. \u201cWe can surmise from this that a major earthquake and tsunami occurred about every 600 to 900 years,\u201d said Engelhart, URI assistant professor of geosciences. \u201cBut those are maximum recurrences. We\u2019re not at a point where we can predict earthquakes.\u201d<\/p>\n


\n\tThe researchers examined a dozen sediment cores up to 6 meters long from two sites near the shoreline of Sumatra\u2019s Aceh province. Within the sediments in the cores were three layers of soil containing mangrove pollen that dropped into the intertidal zone during earthquakes and were buried by tidal flat sediments. Sands above the soils contained species of marine organisms called foraminifera that live far offshore, evidence that the sand was brought onshore by ancient tsunamis. <\/p>\n


\nRadiocarbon dating of these soil layers and associated sands found that local earthquakes causing tsunamis occurred about 7,000, 5,800 and 3,800 years ago. Two turbid layers in the cores containing more oceanic foraminifera were evidence of additional tsunamis that took place during the same period. <\/p>\n


\n\t\u201cThe archive of sedimentary evidence in the cores doesn\u2019t tell the whole story, though,\u201d Engelhart said. \u201cWe had to figure out what the sea level was doing for the last 8,000 years to identify when we would find geological records of earthquakes and tsunamis.\u201d<\/p>\n


\n\tAccording to Engelhart, sea level rose rapidly in the Indian Ocean up until about 8,000 years ago, when it slowed to a rate that allowed sediment to accumulate in predictable layers, enabling present-day scientists to study the environment of the time. About 3,800 years ago, however, sea level gradually stopped rising and sediments no longer accumulated. Instead, wave action mixed up the newer sands, blurring the historic chronology.<\/p>\n


\nEven so, the research team was able to calculate the proportion of sediment that came from offshore in tsunamis by examining the number of fossilized forams that are typically found far out at sea. From this, they concluded that four to six tsunamis struck Sumatra in the last 3,800 years.<\/p>\n


\n\tFor Engelhart, part of the relevance of this study is in the realization of the importance of sea level in conducting this type of analysis. <\/p>\n


\n\u201cYou need to understand how sea level varied at a site before you can think about the methods to improve our understanding of how often earthquakes and tsunamis occur and how big they are,\u201d he said. \u201cThe relative sea-level history of this region demonstrates that we couldn’t use the classic sedimentary methods to reconstruct earthquakes and tsunamis during the last 3,800 years at these sites.\u201d <\/p>\n


\n\tUnderstanding the relative sea-level history will be especially important when scientists conduct analyses of earthquake-prone areas like Alaska, Chile, Peru, Japan and New Zealand, all of which have sea level records that raise similar issues. Engelhart is already applying these findings to related studies in Alaska and the west coast of North America at Cascadia.<\/p>\n


\nPictured above.

\nSimon Engelhart (Photo by Robert Witter)<\/div>\n","protected":false},"excerpt":{"rendered":"

Sea level history vital to estimating earthquake, tsunami history KINGSTON, R.I. \u2013 August 24, 2015 \u2013 The devastating 2004 Indian Ocean earthquake and tsunami that killed 230,000 people has raised questions among coastal residents about when the next big tsunami will strike. It\u2019s a question that University of Rhode Island geologist Simon Engelhart knows cannot […]<\/p>\n","protected":false},"author":2,"featured_media":57485,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[],"class_list":["post-57483","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-archives"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/posts\/57483","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/comments?post=57483"}],"version-history":[{"count":0,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/posts\/57483\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/media\/57485"}],"wp:attachment":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/media?parent=57483"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/categories?post=57483"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/tags?post=57483"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}