Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska
Seismic hazard models for Alaska require estimates of the size and frequency of prehistoric megathrust earthquakes. However, observations that place limits on the size of subduction paleoearthquakes along the Alaska-Aleutian subduction zone are scarce. To help place bounds on the along-strike extent...
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ftvirginiatec:oai:vtechworks.lib.vt.edu:10919/105104 2024-05-19T07:43:31+00:00 Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska Prater, Alexa Brianne Geosciences Dura, Tina Spotila, James A. Romans, Brian W. Alaska 2021-09-28 ETD application/pdf http://hdl.handle.net/10919/105104 unknown Virginia Tech vt_gsexam:32617 http://hdl.handle.net/10919/105104 In Copyright http://rightsstatements.org/vocab/InC/1.0/ paleoseismology earthquakes tsunamis diatoms Alaska Thesis 2021 ftvirginiatec 2024-04-24T00:31:41Z Seismic hazard models for Alaska require estimates of the size and frequency of prehistoric megathrust earthquakes. However, observations that place limits on the size of subduction paleoearthquakes along the Alaska-Aleutian subduction zone are scarce. To help place bounds on the along-strike extent of prehistoric Alaska-Aleutian subduction ruptures, we present stratigraphic and microfossil evidence of repeated tsunami inundation over the last ~400 years at Sitkalidak Island, located 0.5 km off the coast of south-central Kodiak Island. Peat cores collected from an estuary in southern Sitkalidak Island reveal three anomalous, laterally continuous sand beds with sharp upper and lower contacts preserved within a coastal peat sequence. The microfossil and lithostratigraphic characteristics of the sand beds, including the presence of anomalous marine planktonic diatoms, high fragmentation of diatoms, and upward fining sand sequences, indicate high-energy marine incursions consistent with tsunami inundation. Radiocarbon dating constrains the deposition of the sand beds to AD 1964, AD 1788, and ~400 cal yr B.P. The peat core stratigraphy and dates are consistent with tidal wetland stratigraphic records observed at sites ~90 km to the west at Sitkinak Island, and ~80 km to the east at Middle Bay, Kodiak Island. Diatom results from Sitkalidak Island suggest decimeter-scale subsidence during the deposition of the 1964 CE and 1788 CE sand bed. Deformation concurrent with the 1964 and 1788 ruptures along with the presence of a sand bed associated with the ~400 cal yr BP rupture at Sitkalidak help better define the western and eastern rupture limits, and thus the permissible maximum magnitudes, of past Alaska-Aleutian subduction zone ruptures. Master of Science The Alaska-Aleutian subduction zone experiences frequent great earthquakes over magnitude 8 which often produce far-reaching tsunamis. Seismic hazard models that help coastal communities predict and prepare for future hazards require estimates of the size and ... Thesis Kodiak Alaska VTechWorks (VirginiaTech) |
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op_collection_id |
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topic |
paleoseismology earthquakes tsunamis diatoms Alaska |
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paleoseismology earthquakes tsunamis diatoms Alaska Prater, Alexa Brianne Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska |
topic_facet |
paleoseismology earthquakes tsunamis diatoms Alaska |
description |
Seismic hazard models for Alaska require estimates of the size and frequency of prehistoric megathrust earthquakes. However, observations that place limits on the size of subduction paleoearthquakes along the Alaska-Aleutian subduction zone are scarce. To help place bounds on the along-strike extent of prehistoric Alaska-Aleutian subduction ruptures, we present stratigraphic and microfossil evidence of repeated tsunami inundation over the last ~400 years at Sitkalidak Island, located 0.5 km off the coast of south-central Kodiak Island. Peat cores collected from an estuary in southern Sitkalidak Island reveal three anomalous, laterally continuous sand beds with sharp upper and lower contacts preserved within a coastal peat sequence. The microfossil and lithostratigraphic characteristics of the sand beds, including the presence of anomalous marine planktonic diatoms, high fragmentation of diatoms, and upward fining sand sequences, indicate high-energy marine incursions consistent with tsunami inundation. Radiocarbon dating constrains the deposition of the sand beds to AD 1964, AD 1788, and ~400 cal yr B.P. The peat core stratigraphy and dates are consistent with tidal wetland stratigraphic records observed at sites ~90 km to the west at Sitkinak Island, and ~80 km to the east at Middle Bay, Kodiak Island. Diatom results from Sitkalidak Island suggest decimeter-scale subsidence during the deposition of the 1964 CE and 1788 CE sand bed. Deformation concurrent with the 1964 and 1788 ruptures along with the presence of a sand bed associated with the ~400 cal yr BP rupture at Sitkalidak help better define the western and eastern rupture limits, and thus the permissible maximum magnitudes, of past Alaska-Aleutian subduction zone ruptures. Master of Science The Alaska-Aleutian subduction zone experiences frequent great earthquakes over magnitude 8 which often produce far-reaching tsunamis. Seismic hazard models that help coastal communities predict and prepare for future hazards require estimates of the size and ... |
author2 |
Geosciences Dura, Tina Spotila, James A. Romans, Brian W. |
format |
Thesis |
author |
Prater, Alexa Brianne |
author_facet |
Prater, Alexa Brianne |
author_sort |
Prater, Alexa Brianne |
title |
Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska |
title_short |
Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska |
title_full |
Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska |
title_fullStr |
Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska |
title_full_unstemmed |
Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska |
title_sort |
stratigraphic and microfossil evidence of repeated late holocene tsunami inundation at sitkalidak island, alaska |
publisher |
Virginia Tech |
publishDate |
2021 |
url |
http://hdl.handle.net/10919/105104 |
op_coverage |
Alaska |
genre |
Kodiak Alaska |
genre_facet |
Kodiak Alaska |
op_relation |
vt_gsexam:32617 http://hdl.handle.net/10919/105104 |
op_rights |
In Copyright http://rightsstatements.org/vocab/InC/1.0/ |
_version_ |
1799483240979890176 |