A Tsunami about 1000 years ago in Puget Sound, Washington PDF Download

Author: Brian F. Atwater
Publisher:
ISBN:
Category : Earthquakes
Languages : en
Pages : 4

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Author: Carolyn E. Garrison-Laney
Publisher:
ISBN:
Category :
Languages : en
Pages : 151

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Tidal marsh deposits in the Puget Sound area contain evidence for multiple earthquakes and tsunamis over the past 1,000 years. This dissertation focuses on evidence beneath a salt marsh at Lynch Cove, at the head of the Hood Canal about 40 kilometers southwest of Seattle. Previous work at this marsh described stratigraphic evidence for coseismic uplift and liquefaction from a crustal earthquake or earthquakes about 1,000 years ago. New findings from Lynch Cove include two anomalous silt layers interpreted as tsunami deposits that postdate the earthquake uplift and liquefaction. These layers are better explained by tsunamis than by storms or river floods, based on the layer morphology, extent, sedimentology, and microfossils. Radiocarbon ages of the two silt layers at Lynch Cove are 1690–1830 A.D. (120–260 cal yr BP, layer A), and 1170–1230 A.D. (720–780 cal yr BP, layer B). These ages more closely align with the ages of two Cascadia earthquakes than with any other known earthquake in the Puget Sound region within the last 1,000 years. These the silt layers may have been deposited by tsunamis generated by Cascadia subduction thrust earthquakes, as were likely correlative deposits at another tidal marsh at Discovery Bay, along the tsunami path between the Pacific Ocean and Hood Canal. This study improves the age ranges of the youngest six tsunami deposits at Discovery Bay, and compares them to layers A and B at Lynch Cove, and to the ages of known earthquakes and their secondary effects, including tsunamis and slope failures, of the last 1,200 years in the Pacific Northwest. Beds 1 and 3 at Discovery Bay are attributed to Cascadia subduction thrust tsunamis, and have radiocarbon ages that overlap with the ages of layers A and B at Lynch Cove. Discovery Bay Bed 2 has now been dated to 560-630 cal yr BP (1320-1390 A.D.). It is unclear why no corresponding deposit is present between layers A and B at Lynch Cove, and why no known 14th-century coseismic subsidence or tsunami is preserved at any of the Pacific coast estuaries of southern Washington. The source of the tsunami that deposited Discovery Bay Bed 2 remains to be determined. If the source was a rupture along the Cascadia subduction thrust, it may have been limited to an area offshore southern British Columbia and northern Washington, on the northern end of the subduction zone. To test whether Cascadia tsunamis could have deposited the silt layers at Lynch Cove and Discovery Bay, numerical tsunami simulations were run for three different rupture styles of great Cascadia earthquakes, a local Seattle fault tsunami, and a transoceanic tsunami from Alaska. The Cascadia earthquake tsunami simulations produced flow depths and current speeds sufficient to deposit the silt layers at both Lynch Cove and Discovery Bay, while the Seattle fault simulation did not. The Alaska tsunami simulation also produced flooding at Lynch Cove and Discovery Bay, in agreement with historical observations from 1964. Using the inferred tsunami deposits at Lynch Cove as time markers for great Cascadia earthquakes, the paleoecology of the last ~1,000 years is reconstructed using fossil diatoms to test whether Lynch Cove, 240 km inland of the deformation front, records any Cascadia earthquake cycle deformation. A diatom transfer function was developed by statistically comparing the fossil diatoms at Lynch Cove to a training set of modern intertidal diatoms from Puget Sound. Using this method, 31 paleomarsh surface elevations were reconstructed, and with radiocarbon ages, a relative sea level curve was constructed. An overall rise in relative sea level of about 2.5 m is estimated at Lynch Cove over the last 1,000 years, a rate that is faster than rates estimated by other Puget Sound studies. Superimposed on this overall relative sea level rise, paleomarsh surface elevations are observed to rise by about 25 cm prior to the deposition of both layers A and B. While these may record Cascadia preseismic deformation, these rises are within the error range of adjacent data points, so are inconclusive. Because of this, Lynch Cove marsh is interpreted as a location that probably does not record Cascadia earthquake cycle vertical deformation. Lynch Cove is the only forearc data point of vertical interseismic deformation for the Cascadia subduction zone, and these negative results provide an inland limit of earthquake cycle deformation. The findings of this research help to better understand hazards from Cascadia earthquakes and tsunamis in the Puget Sound region. The identification of paleotsunami deposits in Hood Canal identifies a tsunami hazard that was previously unknown. The tsunami simulations corroborate the geological evidence, and identify some areas in Puget Sound with greater tsunami hazard. This study also places constraints on the inland limit of Cascadia earthquake deformation. This is important for accurate estimates of areas of strong shaking, which influence earthquake hazard maps, and for geophysical models. This research also influences estimates of earthquake recurrence. If Bed 2 at Discovery Bay is from a northern Cascadia earthquake, recurrence rates at the northern end of the subduction zone may be shorter than current estimates.

Author: Gary C. Howard
Publisher: CRC Press
ISBN: 0429945914
Category : Nature
Languages : en
Pages : 168

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The Puget Sound is a complex fjord-estuary system in Washington State that is connected to the Pacific Ocean by the Juan de Fuca Strait and surrounded by several large population centers. The watershed is enormous, covering nearly 43,000 square kilometers with thousands of rivers and streams. Geological forces, volcanos, Ice Ages, and changes in sea levels make the Sound a biologically dynamic and fascinating environment, as well as a productive ecosystem. Human activity has also influenced the Sound. Humans built several major cities, such as Seattle and Tacoma, have dramatically affected the Puget Sound. This book describes the natural history and evolution of Puget Sound over the last 100 million years through the present and into the future. Key Features Summarizes a complex geological, geographical, and ecological history Reviews how the Puget Sound has changed and will likely change in the future Examines the different roles of various drivers of the Sound’s ecosystem function Includes the role of humans—both first people and modern populations. Explores Puget Sound as an example of general bay ecological and environmental issues

Author:
Publisher:
ISBN:
Category : Geological surveys
Languages : en
Pages : 342

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Author:
Publisher:
ISBN:
Category : Earthquakes
Languages : en
Pages : 46

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Author: Brian F. Atwater
Publisher:
ISBN:
Category : Paleoseismology
Languages : en
Pages : 120

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A geologic history of earthquakes at the Cascadia subduction zone.

Author: Kenji Satake
Publisher: Birkhäuser
ISBN: 3034872798
Category : Science
Languages : en
Pages : 511

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The 1993 Southwest Hokkaido Earthquake of Magnitude 7. 9 (July 12, 22: 17 JST) caused serious tsunami disasters in the southwestern part of Hokkaido, particularly on Okushiri Island (a tiny island off the southwest coast of Hokkaido with a population of about 4,500 at the time of earthquake). Of 230 casualties, including 28 missing, about 200 deaths are attributable to the tsunami. We have conducted detailed field surveys of tsunami disasters to learn lessons from this costly natural experiment for the future prevention of similar tsunami disasters. Our field work was conducted in four surveys totaling 39 days. During the first field survey (July 16 through July 21, 1994), we worked mostly on the estimation of the subsidence of Okushiri Island during the earthquake. Hence, our main work on tsunami disasters initiated from the second field survey (July 31 through Aug. 15, 1994). Several groups have conducted detailed surveys of the distribution of tsunami runup height as measured from the level of sea water (TsUJI et al. , 1 994a, b; MATSUTOMI and SHUTO, 1994; GOTO et al. , 1994). Such a precise runup height distribution is essential for characterizing tsunami, including its overall size. Indeed, the height distribution is the fundamental data for inferring earthquake source parameters through the simulation of tsunami generation (TAKAHASHI et al. , 1994; IMAMURA et al. , 1994; TSUJI et al. , 1994a; SATAKE and TANIOKA 1994; ABE, 1994; TANIOKA et al. , in review).

Author: Sandi Doughton
Publisher: Sasquatch Books
ISBN: 1570618550
Category : Nature
Languages : en
Pages : 293

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Scientific reportage on what we know and don’t know about the mega-earthquake predicted to hit the Pacific Northwest Scientists have identified Seattle, Portland, and Vancouver as the urban centers of what will be the biggest earthquake—the Really Big One—in the continental United States. A quake will happen—in fact, it’s actually overdue. The Cascadia subduction zone is 750 miles long, running along the Pacific coast from Northern California up to southern British Columbia. In this fascinating book, The Seattle Times science reporter Sandi Doughton introduces readers to the scientists who are dedicated to understanding the way the earth moves and describes what patterns can be identified and how prepared (or not) people are. With a 100% chance of a mega-quake hitting the Pacific Northwest, this fascinating book reports on the scientists who are trying to understand when, where, and just how big The Big One will be.

Author: United States. Science Review Working Group
Publisher:
ISBN:
Category : Nuclear power plants
Languages : en
Pages : 134

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Author: Ralph A. Haugerud
Publisher: Geological Society of America
ISBN: 0813700493
Category : Science
Languages : en
Pages : 264

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"This volume contains guides that geographically focus on the Seattle, Washington, area within the Puget lowland, and also includes descriptions of trips in the Cascade Range and the region east of the Cascades"--