Transition from locked to creeping subduction in the Shumagin region, Alaska

Fournier, T.; Freymueller, J. T.

doi:10.1029/2006gl029073

Cited by 89 publications

(113 citation statements)

References 25 publications

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“…Observations at Southwest Anchorage are consistent with subsidence in the twentieth century, but rates of apparent subsidence prior to GPS observations that began in 1995 (Fournier and Freymueller, 2007) have not been accurately measured. The strongest evidence of subsidence is the inland migration of the crest of the storm-beach berm at Southwest Anchorage, which we infer was caused by relative sea-level rise during gradual subsidence.…”

Section: Land-level Changes During Earthquake Cyclesmentioning

confidence: 93%

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Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

et al. 2015

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Despite the role of the Alaska-Aleutian megathrust as the source of some of the largest earthquakes and tsunamis, the history of its pre-twentieth century tsunamis is largely unknown west of the rupture zone of the great (magnitude, M 9.2) 1964 earthquake. Stratigraphy in core transects at two boggy lowland sites on Chirikof Island's southwest coast preserves tsunami deposits dating from the postglacial to the twentieth century. In a 500-m-long basin 13-15 m above sea level and 400 m from the sea, 4 of 10 sandy to silty beds in a 3-5-m-thick sequence of freshwater peat were probably deposited by tsunamis. The freshwater peat sequence beneath a gently sloping alluvial fan 2 km to the east, 5-15 m above sea level and 550 m from the sea, contains 20 sandy to silty beds deposited since 3.5 ka; at least 13 were probably deposited by tsunamis. Although most of the sandy beds have consistent thicknesses (over distances of 10-265 m), sharp lower contacts, good sorting, and/or upward fining typical of tsunami deposits, the beds contain abundant freshwater diatoms, very few brackish-water diatoms, and no marine diatoms. Apparently, tsunamis traveling inland over low dunes and boggy lowland entrained largely freshwater diatoms. Abundant fragmented diatoms, and lake species in some sandy beds not found in host peat, were probably transported by tsunamis to elevations of >10 m at the eastern site. Single-aliquot regeneration optically stimulated luminescence dating of the third youngest bed is consistent with its having been deposited by the tsunami recorded at Russian hunting outposts in 1788, and with the second youngest bed being deposited by a tsunami during an upper plate earthquake in 1880. We infer from stratigraphy, 14 C-dated peat deposition rates, and unpublished analyses of the island's history that the 1938 tsunami may locally have reached an elevation of >10 m. As this is the first record of Aleutian tsunamis extending throughout the Holocene, we cannot estimate source earthquake locations or magnitudes for most tsunami-deposited beds. We infer that no more than 3 of the 23 possible tsunamis beds at both sites were deposited following upper plate faulting or submarine landslides independent of megathrust earthquakes. If so, the Semidi segment of the Alaska-Aleutian megathrust near Chirikof Island probably sent high tsunamis southward every 180-270 yr for at least the past 3500 yr.

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Section: Land-level Changes During Earthquake Cyclesmentioning

confidence: 93%

“…S1 in the Supplemental File [see footnote 1]), as would be expected if the plate boundary beneath the island were accumulating strain to be released in a future earthquake. Geodetic coupling models imply that the megathrust beneath Chirikof Island is 90%-100% locked (Fournier and Freymueller, 2007).…”

Section: Land-level Changes During Earthquake Cyclesmentioning

confidence: 99%

Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

et al. 2015

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“…From the Semidi Islands west to Sanak Island, GPS data show an overall decrease in the slip deficit. There is a transition from a highly coupled zone to a mainly creeping zone occurring over a small area around the Shumagin Islands (Fournier and Freymueller, 2007). East of the Shumagin Islands, the coupling is on the order of 70 percent, with coupling in the area of the Shumagin Islands themselves at about 30 percent .…”

Section: Alongstrike Variations In Plate Couplingmentioning

confidence: 99%

“…There is little trench-perpendicular strain measured at Sanak Island, with the only possibility of a locked zone at very shallow depths (~11 km) near the trench (Fournier and Freymueller, 2007). West of Sanak Island, most of the GPS stations are located on the volcanic arc; however, most stations located away from the influence of volcanism show little slip deficit.…”

Section: Alongstrike Variations In Plate Couplingmentioning

confidence: 99%

History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland

Ryan¹,

Huene²,

Wells³

et al. 2012

Professional Paper

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For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS (1-888-275-8747).To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce any copyrighted items must be secured from the copyright owner. AbstractDuring the past several years, devastating tsunamis were generated along subduction zones in Indonesia, Chile, and most recently Japan.

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“…The largest amount of slip is placed at the eastern end, which is a nearly fully locked segment of the megathrust beneath the Semidi Islands, based on the GPS studies by Freymueller and others (2008). We assign a much smaller amount of slip to the middle part of the rupture, where coupling of the plate interface changes from about 30 percent locked at the Shumagin Islands to freely slipping west of the Shumagins (Fournier and Freymueller, 2007). The amount of slip increases again at the western end of the rupture, where little moment was released in 1957.…”

Section: Scenario 7 Multi-segment Event: Sem Sh Un and Fox Segmentsmentioning

confidence: 88%

Tsunami inundation maps of Sitka, Alaska

Suleimani¹

2013

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Transition from locked to creeping subduction in the Shumagin region, Alaska

Cited by 89 publications

References 25 publications

Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland

Tsunami inundation maps of Sitka, Alaska

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