@article {2975, title = {The giant 1960 tsunami in the context of a 6000-year record of paleotsunamis and coastal evolution in south-central Chile}, journal = {Earth Surface Processes and Landforms}, volume = {47}, year = {2022}, month = {06/2022}, pages = {2062 - 2078}, abstract = {The tsunami associated with the giant 9.5 Mw 1960 Chile earthquake deposited an extensive sand layer above organic-rich soils near Queule (39.3{\textdegree}S, 73.2{\textdegree}W), south-central Chile. Using the 1960 tsunami deposits, together with eye-witness observations and numerical simulations of tsunami inundation, we tested the tsunami inundation sensitivity of the site to different earthquake slip distributions. Stratigraphically below the 1960 deposit are two additional widespread sand layers interpreted as tsunami deposits with maximum ages of 4960{\textendash}4520 and 5930{\textendash}5740 cal BP. This >4500-year gap of tsunami deposits preserved in the stratigraphic record is inconsistent with written and geological records of large tsunamis in south-central Chile in 1575, 1837, and possibly 1737. We explain this discrepancy by: (1) poor preservation of tsunami deposits due to reduced accommodation space from relative sea-level fall during the late Holocene; (2) recently evolved coastal geomorphology that increased sediment availability for tsunami deposit formation in 1960; and/or (3) the possibility that the 1960 tsunami was significantly larger at this particular location than other tsunamis in the past >4500 years. Our research illustrates the complexities of reconstructing a complete stratigraphic record of past tsunamis from a single site for tsunami hazard assessment. The coastal geomorphology near Queule, Chile preserves evidence of the giant Mw 9.51960 Chile earthquake and two buried paleotsunami deposits within the last 6000 years. Using the 1960 tsunami deposits, eye-witness observations, and numerical simulations of tsunami inundation, we tested the sensitivity of the site to different earthquake slip distributions. We consider the role of coastal geomorphic evolution, sea-level history, and tsunami magnitude in the preservation of paleotsunami depositional records.}, doi = {10.1002/esp.5363}, url = {https://onlinelibrary.wiley.com/doi/10.1002/esp.5363}, author = {Matos-Llavona, Pedro I. and Ely, Lisa L. and MacInnes, Breanyn and Dura, Tina and Cisternas, Marco A. and Bourgeois, Joanne and Bruce, David and DePaolis, Jessica and Dolcimascolo, Alexander and Horton, Benjamin P. and Melnick, Daniel and Nelson, Alan R. and Szeliga, Walter and Wesson, Robert L.} } @article {2929, title = {A maximum rupture model for the central and southern Cascadia subduction zone{\textemdash}reassessing ages for coastal evidence of megathrust earthquakes and tsunamis}, journal = {Quaternary Science Reviews}, volume = {261}, year = {2021}, month = {Jan-06-2021}, pages = {106922}, abstract = {A new history of great earthquakes (and their tsunamis) for the central and southern Cascadia subduction zone shows more frequent (17 in the past 6700 yr) megathrust ruptures than previous coastal chronologies. The history is based on along-strike correlations of Bayesian age models derived from evaluation of 554 radiocarbon ages that date earthquake evidence at 14 coastal sites. We reconstruct a history that accounts for all dated stratigraphic evidence with the fewest possible ruptures by evaluating the sequence of age models for earthquake or tsunami contacts at each site, comparing the degree of temporal overlap of correlated site age models, considering evidence for closely spaced earthquakes at four sites, and hypothesizing only maximum-length megathrust ruptures. For the past 6700 yr, recurrence for all earthquakes is 370e420 yr. But correlations suggest that ruptures at-1.5 ka and-1.1 ka were of limited extent (<400 km). If so, post-3-ka recurrence for ruptures extending throughout central and southern Cascadia is 510e540 yr. But the range in the times between earthquakes is large: two instances may be-50 yr, whereas the longest are-550 and-850 yr. The closely spaced ruptures about 1.6 ka may illustrate a pattern common at subduction zones of a long gap ending with a great earthquake rupturing much of the subduction zone, shortly followed by a rupture of more limited extent. The ruptures of limited extent support the continued inclusion of magnitude-8 earthquakes, with longer ruptures near magnitude 9, in assessments of seismic hazard in the region. }, issn = {02773791}, doi = {10.1016/j.quascirev.2021.106922}, url = {https://apps.webofknowledge.com/InboundService.do?product=WOS\&Func=Frame\&DestFail=http\%3A\%2F\%2Fwww.webofknowledge.com\&SrcApp=search\&SrcAuth=Alerting\&SID=6DMZZppDlBSzMpeHDG2\&customersID=Alerting\&mode=FullRecord\&IsProductCode=Yes\&AlertId=4d48b20a-7d27-4fa2-}, author = {Nelson, Alan R. and DuRoss, Christopher B. and Witter, Robert C. and Kelsey, Harvey M. and Engelhart, Simon E. and Mahan, Shannon A. and Gray, Harrison J. and Hawkes, Andrea D. and Horton, Benjamin P. and Padgett, Jason S.} } @article {2776, title = {Identifying the Greatest Earthquakes of the Past 2000 Years at the Nehalem River Estuary, Northern Oregon Coast, USA}, journal = {Open Quaternary}, volume = {6}, year = {2020}, month = {Feb-01-2021}, abstract = {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 {\textpm} 0.5 m); B, 942{\textendash}764 cal a BP (0.7 {\textpm} 0.4 m and 1.0 m {\textpm} 0.4 m); and D, 1568{\textendash}1361 cal a BP (1.0 m {\textpm} 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.}, keywords = {Bayesian transfer function, Cascadia subduction zone, Coseismic subsidence, earthquake hazards, Paleoseismology, salt-marsh stratigraphy, Sea-level changes, tidal foraminifera and diatoms}, doi = {10.5334/oq.70}, url = {http://www.openquaternary.com/articles/10.5334/oq.70/}, author = {Nelson, Alan R. and Hawkes, Andrea D. and Sawai, Yuki and Engelhart, Simon E. and Witter, Rob and Grant-Walter, Wendy C. and Bradley, Lee-Ann and Dura, Tina and Cahill, Niamh and Horton, Ben} } @article {2834, title = {Sedimentary evidence of prehistoric distant-source tsunamis in the Hawaiian Islands}, journal = {Sedimentology}, volume = {67}, year = {2020}, month = {Jan-04-2020}, pages = {1249 - 1273}, abstract = {Over the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific {\textquoteleft}Ring of Fire{\textquoteright} (for example, Alaska{\textendash}Aleutian, Kuril{\textendash}Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low-lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north-eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon-based age models date sand beds from three sites to ca 700 to 500 cal yr bp, which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands.}, keywords = {Aleutians, deposit, distant source, extreme events, Hawai΄i, palaeotsunami}, issn = {0037-0746}, doi = {10.1111/sed.12623}, url = {https://onlinelibrary.wiley.com/doi/10.1111/sed.12623}, author = {La Selle, SeanPaul and Richmond, Bruce M. and Jaffe, Bruce E. and Nelson, Alan R. and Griswold, Frances R. and Arcos, Maria E. M. and Chagu{\'e}, Catherine and Bishop, James M. and Bellanova, Piero and Kane, Haunani H. and Lunghino, Brent D. and Gelfenbaum, Guy}, editor = {Costa, Pedro} } @article {2768, title = {Subduction zone slip variability during the last millennium, south-central Chile}, journal = {Quaternary Science Reviews}, volume = {175}, year = {2017}, month = {Jan-11-2017}, pages = {112 - 137}, abstract = {The Arauco Peninsula (37{\textdegree}-38{\textdegree}S) in south-central Chile has been proposed as a possible barrier to the along-strike propagation of megathrust ruptures, separating historical earthquakes to the south (1960 AD 1837, 1737, and 1575) and north (2010 AD, 1835, 1751, 1657, and 1570) of the peninsula. However, the 2010 (Mw 8.8) earthquake propagated into the Arauco Peninsula, re-rupturing part of the megathrust that had ruptured only 50 years earlier during the largest subduction zone earthquake in the instrumental record (Mw 9.5). To better understand long-term slip variability in the Arauco Peninsula region, we analyzed four coastal sedimentary sections from two sites (Tir{\'u}a, 38.3{\textdegree}S and Quidico, 38.1{\textdegree}S) located within the overlap of the 2010 and 1960 ruptures to reconstruct a \~{}600-year record of coseismic land-level change and tsunami inundation. Stratigraphic, lithologic, and diatom results show variable coseismic land-level change coincident with tsunami inundation of the Tir{\'u}a and Quidico marshes that is consistent with regional historical accounts of coseismic subsidence during earthquakes along the Valdivia portion of the subduction zone (1960 AD and 1575) and coseismic uplift during earthquakes along the Maule portion of the subduction zone (2010 AD, 1835, 1751). In addition, we document variable coseismic land-level change associated with three new prehistoric earthquakes and accompanying tsunamis in 1470{\textendash}1570 AD, 1425{\textendash}1455, and 270{\textendash}410. The mixed record of coseismic subsidence and uplift that we document illustrates the variability of down-dip and lateral slip distribution at the overlap of the 2010 and 1960 ruptures, showing that ruptures have repeatedly propagated into, but not through the Arauco Peninsula and suggesting the area has persisted as a long-term impediment to slip through at least seven of the last megathrust earthquakes (\~{}600 years).}, keywords = {Coastal hazards, Coastal paleoseismology, Diatom paleoecology, Prehistoric earthquakes, Subduction zone segmentation, Tsunami Deposits}, issn = {02773791}, doi = {10.1016/j.quascirev.2017.08.023}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0277379117303505}, author = {Dura, Tina and Horton, Benjamin P. and Cisternas, Marco and Ely, Lisa L. and Hong, Isabel and Nelson, Alan R. and Wesson, Robert L. and Pilarczyk, Jessica E. and Parnell, Andrew C. and Nikitina, Daria} } @article {2597, title = {Differences in coastal subsidence in southern Oregon (USA) during at least six prehistoric megathrust earthquakes}, journal = {Quaternary Science Reviews}, volume = {142}, year = {2016}, month = {Jan-06-2016}, pages = {143 - 163}, abstract = {Stratigraphic, sedimentologic (including CT 3D X-ray tomography scans), foraminiferal, and radiocarbon analyses show that at least six of seven abrupt peat-to-mud contacts in cores from a tidal marsh at Talbot Creek (South Slough, Coos Bay), record sudden subsidence (relative sea-level rise) during great megathrust earthquakes at the Cascadia subduction zone. Data for one contact are insufficient to infer whether or not it records a great earthquake{\textemdash}it may also have formed through local, non-seismic, hydrographic processes. To estimate the amount of subsidence marked by each contact, we expanded a previous regional modern foraminiferal dataset to 174 samples from six Oregon estuaries. Using a transfer function derived from the new dataset, estimates of coseismic subsidence across the six earthquake contacts vary from 0.31 m to 0.75 m. Comparison of subsidence estimates for three contacts in adjacent cores shows within-site differences of <=0.10 m, about half the {\textpm}0.22 m error, although some estimates may be minimums due to uncertain ecological preferences for Balticammina pseudomacrescens in brackish environments and almost monospecific assemblages of Miliammina fusca on tidal flats. We also account for the influence of taphonomic processes, such as infiltration of mud with mixed foraminiferal assemblages into peat, on subsidence estimates. Comparisons of our subsidence estimates with values for correlative contacts at other Oregon sites suggest that some of our estimates are minimums and that Cascadia{\textquoteright}s megathrust earthquake ruptures have been heterogeneous over the past 3500 years.}, keywords = {Cascadia subduction zone, Coseismic subsidence, Megathrust earthquakes, Paleoseismology, Salt-marsh foraminifera, Sea-level change, Transfer functions}, issn = {02773791}, doi = {10.1016/j.quascirev.2016.04.017}, url = {https://doi.org/10.1016/j.quascirev.2016.04.017}, author = {Milker, Yvonne and Nelson, Alan R. and Horton, Benjamin P. and Engelhart, Simon E. and Bradley, Lee-Ann and Witter, Robert C.} } @article {2595, title = {Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile}, journal = {Quaternary Science Reviews}, volume = {113}, year = {2015}, month = {Jan-04-2015}, pages = {93 - 111}, abstract = {The \~{}500-year historical record of seismicity along the central Chile coast (30{\textendash}34{\textdegree}S) is characterized by a series of \~{}M 8.0{\textendash}8.5 earthquakes followed by low tsunamis (<4 m) occurring on the megathrust about every 80 years. One exception is the AD 1730 great earthquake (M 9.0{\textendash}9.5) and high tsunami (>10 m), but the frequency of such large events is unknown. We extend the seismic history of central Chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of Valpara{\'\i}so (33{\textdegree}S). At this site, higher relative sea level during the mid Holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence. Within this 2600-yr-long sequence, we traced six laterally continuous sand beds probably deposited by high tsunamis. Plant remains that underlie the sand beds were radiocarbon dated to 6200, 5600, 5000, 4400, 3800, and 3700 cal yr BP. Sediment properties and diatom assemblages of the sand beds{\textemdash}for example, anomalous marine planktonic diatoms and upward fining of silt-sized diatom valves{\textemdash}point to a marine sediment source and high-energy deposition. Grain-size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment. Upward fining sequences characteristic of suspension deposition are present in five of the six sand beds. Despite the lack of significant lithologic changes between the sedimentary units under- and overlying tsunami deposits, we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds. During our mid-Holocene window of evidence preservation, the mean recurrence interval of earthquakes and tsunamis is \~{}500 years. Our findings imply that the frequency of historical earthquakes in central Chile is not representative of the greatest earthquakes and tsunamis that the central Chilean subduction zone has produced.}, keywords = {Coastal hazards, Coastal paleoseismology, Diatom paleoecology, Prehistoric earthquakes, Tsunami Deposits}, issn = {02773791}, doi = {10.1016/j.quascirev.2014.10.015}, url = {https://doi.org/10.1016/j.quascirev.2014.10.015}, author = {Dura, Tina and Cisternas, Marco and Horton, Benjamin P. and Ely, Lisa L. and Nelson, Alan R. and Wesson, Robert L. and Pilarczyk, Jessica E.} } @article {2596, title = {A sea-level database for the Pacific coast of central North America}, journal = {Quaternary Science Reviews}, volume = {113}, year = {2015}, month = {Jan-04-2015}, pages = {78 - 92}, abstract = {A database of published and new relative sea-level (RSL) data for the past 16 ka constrains the sea-level histories of the Pacific coast of central North America (southern British Columbia to central California). Our reevaluation of the stratigraphic context and radiocarbon age of sea-level indicators from geological and archaeological investigations yields 600 sea-level index points and 241 sea-level limiting points. We subdivided the database into 12 regions based on the availability of data, tectonic setting, and distance from the former Cordilleran ice sheet. Most index (95\%) and limiting points (54\%) are <7 ka; older data come mainly from British Columbia and San Francisco Bay. The stratigraphic position of points was used as a first-order assessment of compaction. Formerly glaciated areas show variable RSL change; where data are present, highstands of RSL occur immediately post-deglaciation and in the mid to late Holocene. Sites at the periphery and distant to formerly glaciated areas demonstrate a continuous rise in RSL with a decreasing rate through time due to the collapse of the peripheral forebulge and the reduction in meltwater input during deglaciation. Late Holocene RSL change varies spatially from falling at 0.7 {\textpm} 0.8 mm a-1 in southern British Columbia to rising at 1.5 {\textpm} 0.3 mm a-1 in California. The different sea-level histories are an ongoing isostatic response to deglaciation of the Cordilleran and Laurentide Ice Sheets.}, keywords = {Cascadia subduction zone, Glacial isostatic adjustment, Holocene, Pacific North America, Sea-level database}, issn = {02773791}, doi = {10.1016/j.quascirev.2014.12.001}, url = {https://doi.org/10.1016/j.quascirev.2014.12.001}, author = {Engelhart, Simon E. and Vacchi, Matteo and Horton, Benjamin P. and Nelson, Alan R. and Kopp, Robert E.} } @article {2591, title = {Diverse rupture modes for surface-deforming upper-plate earthquakes in the southern Puget Lowland of Washington State}, journal = {Geosphere}, volume = {10}, year = {2014}, month = {Jan-01-2014}, pages = {769}, abstract = {Earthquake prehistory of the southern Puget Lowland, in the north-south compressive regime of the migrating Cascadia forearc, reflects diverse earthquake rupture modes with variable recurrence. Stratigraphy and Bayesian analyses of previously reported and new 14C ages in trenches and cores along backthrust scarps in the Seattle fault zone restrict a large earthquake to 1040{\textendash}910 cal yr B.P. (2σ), an interval that includes the time of the M 7{\textendash}7.5 Restoration Point earthquake. A newly identified surface-rupturing earthquake along the Waterman Point backthrust dates to 940{\textendash}380 cal yr B.P., bringing the number of earthquakes in the Seattle fault zone in the past 3500 yr to 4 or 5. Whether scarps record earthquakes of moderate (M 5.5{\textendash}6.0) or large (M 6.5{\textendash}7.0) magnitude, backthrusts of the Seattle fault zone may slip during moderate to large earthquakes every few hundred years for periods of 1000{\textendash}2000 yr, and then not slip for periods of at least several thousands of years. Four new fault scarp trenches in the Tacoma fault zone show evidence of late Holocene folding and faulting about the time of a large earthquake or earthquakes inferred from widespread coseismic subsidence ca. 1000 cal yr B.P.; 12 ages from 8 sites in the Tacoma fault zone limit the earthquakes to 1050{\textendash}980 cal yr B.P. Evidence is too sparse to determine whether a large earthquake was closely predated or postdated by other earthquakes in the Tacoma basin, but the scarp of the Tacoma fault was formed by multiple earthquakes. In the northeast-striking Saddle Mountain deformation zone, along the western limit of the Seattle and Tacoma fault zones, analysis of previous ages limits earthquakes to 1200{\textendash}310 cal yr B.P. The prehistory clarifies earthquake clustering in the central Puget Lowland, but cannot resolve potential structural links among the three Holocene fault zones.}, issn = {1553040X}, doi = {10.1130/GES00967.110.1130/GES00967.S1}, url = {https://pubs.geoscienceworld.org/geosphere/article/10/4/769-796/132175}, author = {Nelson, Alan R. and Personius, Stephen F. and Sherrod, Brian L. and Kelsey, Harvey M. and Johnson, Samuel Y. and Bradley, Lee-Ann and Wells, Ray E.} } @article {2593, title = {Uplift and subsidence reveal a nonpersistent megathrust rupture boundary (Sitkinak Island, Alaska)}, journal = {Geophysical Research Letters}, volume = {41}, year = {2014}, month = {Apr-04-2015}, pages = {2289 - 2296}, abstract = {We report stratigraphic evidence of land-level change and tsunami inundation along the Alaska-Aleutian megathrust during prehistoric and historical earthquakes west of Kodiak Island. On Sitkinak Island, cores and tidal outcrops fringing a lagoon reveal five sharp lithologic contacts that record coseismic land-level change. Radiocarbon dates, 137Cs profiles, computerized tomography scans, and microfossil assemblages are consistent with rapid uplift circa 290{\textendash}0, 520{\textendash}300, and 1050{\textendash}790 cal yr B.P. and subsidence in A.D. 1964 and circa 640{\textendash}510 cal yr B.P. Radiocarbon, 137Cs, and 210Pb ages bracketing a sand bed traced 1.5 km inland and evidence for sudden uplift are consistent with Russian accounts of an earthquake and tsunami in A.D. 1788. The mixed uplift and subsidence record suggests that Sitkinak Island sits above a nonpersistent boundary near the southwestern limit of the A.D. 1964 Mw 9.2 megathrust rupture.}, doi = {10.1002/2014GL059380}, url = {http://doi.wiley.com/10.1002/2014GL059380}, author = {Briggs, Richard W. and Engelhart, Simon E. and Nelson, Alan R. and Dura, Tina and Kemp, Andrew C. and Haeussler, Peter J. and Corbett, D. Reide and Angster, Stephen J. and Bradley, Lee-Ann} } @article {2590, title = {Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates}, journal = {Journal of Geophysical Research: Solid Earth}, volume = {118}, year = {2013}, month = {Jan-05-2013}, pages = {2460 - 2473}, abstract = {Past earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great A.D. 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here we infer heterogeneous slip for the Cascadia margin in A.D. 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of then available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3-D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extensions, the more precise subsidence estimates are best explained by a model with along-strike slip heterogeneity, with multiple patches of high-moment release separated by areas of low-moment release. For example, in A.D. 1700, there was very little slip near Alsea Bay, Oregon (~44.4{\textdegree}N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for more precise, high-quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47{\textdegree}N), southernmost Oregon, and northern California (south of 43{\textdegree}N), where slip distributions of prehistoric earthquakes are poorly constrained.}, doi = {10.1002/jgrb.50101}, url = {http://doi.wiley.com/10.1002/jgrb.50101}, author = {Wang, Pei-Ling and Engelhart, Simon E. and Wang, Kelin and Hawkes, Andrea D. and Horton, Benjamin P. and Nelson, Alan R. and Witter, Robert C.} } @article {291, title = {Fragmentary Evidence of Great-Earthquake Subsidence during Holocene Emergence, Valdivia Estuary, South Central Chile}, journal = {Bulletin of the Seismological Society of America}, volume = {99}, year = {2009}, note = {id: 2020; PT: J; UT: WOS:000266181100006}, pages = {71-86}, abstract = {A reconnaissance of Holocene stratigraphy beneath fringing marshes of the Valdivia estuary, where an M 9.5 earthquake caused 1-2 m of regional coseismic subsidence in 1960, shows only fragmentary evidence of prehistoric coseismic subsidence. In most of the 150 hand-driven cores that were examined, a distinct unconformity separates 0.5-1.5 m of late Holocene tidal and floodplain mud, peat, and sand from underlying middle Holocene subtidal mud and sand. At the Las Coloradas site, where stratigraphy is best preserved, two A horizons of marsh and meadow soils abruptly overlain by sand and mud probably record coseismic subsidence shortly followed by tsunamis. The amount of subsidence during the earthquakes proved difficult to reconstruct with a diatom transfer function because of differences between modern and fossil diatom assemblages. Maximum (14)C ages on macrofossils from the two A horizons at the Las Coloradas site of 1.7-1.3 ka and 2.7-1.7 ka allow correlation of the younger horizon with either of two of six (14)C-dated A horizons buried by tsunami sand or post-tsunami tidal sand 200 km to the south at Maullin, and with a lake-wide mass wasting event in Lago Puyehue, 100 km to the southeast. Tidal records of prehistoric coseismic subsidence at Valdivia are scarce because of a sea-level fall of 3-8 m over the past 6000 years, erosion of marsh and meadow soils during subsidence-induced flooding of the estuary, and largely complete land-level recovery during cycles of coseismic subsidence and postseismic uplift.}, issn = {0037-1106}, doi = {10.1785/0120080103}, author = {Nelson, Alan R. and Kashima, Kaoru and Bradley, Lee-Ann} } @article {327, title = {Earthquakes generated from bedding plane-parallel reverse faults above an active wedge thrust, Seattle fault zone}, journal = {Geological Society of America Bulletin}, volume = {120}, year = {2008}, note = {id: 2019; PT: J; UT: WOS:000260737900015}, pages = {1581-1597}, abstract = {A key question in earthquake hazard analysis is whether individual faults within fault zones represent independent seismic sources. For the Seattle fault zone, an upper plate structure within the Cascadia convergent margin, evaluating seismic hazard requires understanding how north-side-up, bedding-plane reverse faults, which generate late Holocene fault scarps, interact with the north-vergent master-ramp thrust and overlying backthrust of the fault zone. A regional uplift at A.D. 900-930 involved an earthquake that nucleated at depth and included slip on both the master-ramp thrust and the backthrust. This earthquake also included slip on some of the}, issn = {0016-7606}, doi = {10.1130/B26282.1}, author = {Kelsey, Harvey M. and Sherrod, Brian L. and Nelson, Alan R. and Brocher, Thomas M.} } @article {2037, title = {Artifacts from a submerged prehistoric site on the Coos Bay Estuary, southern Oregon coast}, journal = {Journal of California and Great Basin Anthropology}, volume = {24}, year = {2004}, note = {id: 993}, month = {2004}, pages = {41-52}, author = {Minor, Rick and Nelson, Alan R.} } @article {2136, title = {Optical dating, ages, and scatter from tsunami-laid sands from Bradley Lake, Oregon}, journal = {Quaternary Science Reviews}, volume = {20}, year = {2001}, note = {id: 1406}, month = {2001}, pages = {1915-1926}, author = {Ollerhead, Jeff and Huntley, David J. and Nelson, Alan R. and Kelsey, Harvey M.} }