Identifying the Greatest Earthquakes of the Past 2000 Years at the Nehalem River Estuary, Northern Oregon Coast, USA

Open Quaternary

卷:6

Rob Witter¹  Ben Horton²  Andrea D. Hawkes³  Simon E. Engelhart⁴  Tina Dura⁵  Niamh Cahill⁶  Alan R. Nelson⁷  Lee-Ann Bradley⁷  Wendy C. Grant-Walter⁸  Yuki Sawai⁹ 

[1] Alaska Science Center, U.S. Geological Survey, Anchorage, Alaska;

[2] Asian School of the Environment, Nanyang Technological University;

[3] Department of Earth and Ocean Sciences, University of North Carolina Wilmington, Wilmington, North Carolina;

[4] Department of Geography, Durham University, Durham;

[5] Department of Geosciences, Virginia Tech, Blacksburg, Virginia;

[6] Department of Mathematics and Statistics, Maynooth University, Kildare;

[7] Geologic Hazards Science Center, U.S. Geological Survey, Golden, Colorado;

[8] Harwich Port, MA;

[9] National Institute of Advanced Industrial Science and Technology, Tsukuba;

关键词: paleoseismology;    cascadia subduction zone;    tidal foraminifera and diatoms;    coseismic subsidence;    bayesian transfer function;    sea-level changes;    salt-marsh stratigraphy;    earthquake hazards;   

DOI  :  10.5334/oq.70

来源: DOAJ

【 摘 要 】

We infer a history of three great megathrust earthquakes during the past 2000 years at the Nehalem River estuary based on the lateral extent of sharp (≤3 mm) peat-mud stratigraphic contacts in cores and outcrops, coseismic subsidence as interpreted from fossil diatom assemblages and reconstructed with foraminiferal assemblages using a Bayesian transfer function, and regional correlation of 14C-modeled ages for the times of subsidence. A subsidence contact from 1700 CE (contact A), sometimes overlain by tsunami-deposited sand, can be traced over distances of 7 km. Contacts B and D, which record subsidence during two earlier megathrust earthquakes, are much less extensive but are traced across a 700-m by 270-m tidal marsh. Although some other Cascadia studies report evidence for an earthquake between contacts B and D, our lack of extensive evidence for such an earthquake may result from the complexities of preserving identifiable evidence of it in the rapidly shifting shoreline environments of the lower river and bay. Ages (95% intervals) and subsidence for contacts are: A, 1700 CE (1.1 ± 0.5 m); B, 942–764 cal a BP (0.7 ± 0.4 m and 1.0 m ± 0.4 m); and D, 1568–1361 cal a BP (1.0 m ± 0.4 m). Comparisons of contact subsidence and the degree of overlap of their modeled ages with ages for other Cascadia sites are consistent with megathrust ruptures many hundreds of kilometers long. But these data cannot conclusively distinguish among different types or lengths of ruptures recorded by the three great earthquake contacts at the Nehalem River estuary.

【 授权许可】

Unknown