The following report summarizes the dating results from Bradley Lake, Oregon. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and datingrelated calculations. We recommend that this report be included as the supplementary material for any publication(s) that use the ages within this report. This version supersedes all previous age estimates and reports.

This data release contains supplemental data for the following paper: Nelson, A.R., DuRoss, C.B., Mahan, S.A., Gray, H.J., Engelhart, S.E., Witter, R.C., Hawkes, A.D., Horton, B.P., Kelsey, H.M., and Padgett, J.S., 2021, A maximum rupture model for the central and southern Cascadia subduction zone—assessing ages for coastal evidence of megathrust earthquakes and tsunamis: Quaternary Science Reviews 261, https://doi.org/10.1016/j.quascirev.2021.106922. The data include a compilation of new and previously published radiocarbon ages from the original cores from Bradley Lake of Kelsey et al. (2005; odt format), and tables of new and previously published radiocarbon data for 7 of the 13 tidal wetland sites along the coasts of Oregon and northern California, whose ages we compare with the ages from Bradley Lake (odt format). The data files (odt format) also include code for the OxCal (version 4.4; https://c14.arch.ox.ac.uk/oxcal.html) Bayesian software models used with selected radiocarbon ages to calculate age probability density functions for the lake’s earthquake or tsunami-caused disturbance events, and for the stratigraphic contacts produced by earthquakes and tsunamis at 12 of the 13 tidal wetland sites (odt format). An additional text file (odt format) explains the addition of variance to the errors on laboratory reported radiocarbon ages in the tables analyzed prior to 1998, and those analyzed by the National Ocean Sciences AMS Facility (NOSAMS) at the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts. Data describing the results of our recent unsuccessful attempt to use optical dating methods (OSL and IRSL) on quartz grains from tsunami deposits in Bradley Lake to date the deposits can be found in Mahan et al. (2021; U.S. Geological Survey data release, https://doi.org/10.5066/P9YWIDOW).

This data release contains supplemental data for the following paper: Nelson, A.R., DuRoss, C.B., Mahan, S.A., Gray, H.J., Engelhart, S.E., Witter, R.C., Hawkes, A.D., Horton, B.P., Kelsey, H.M., and Padgett, J.S., 2021, A maximum rupture model for the central and southern Cascadia subduction zone—assessing ages for coastal evidence of megathrust earthquakes and tsunamis: Quaternary Science Reviews 261, https://doi.org/10.1016/j.quascirev.2021.106922. The data include a compilation of new and previously published radiocarbon ages from the original cores from Bradley Lake of Kelsey et al. (2005; odt format), and tables of new and previously published radiocarbon data for 7 of the 13 tidal wetland sites along the coasts of Oregon and northern California, whose ages we compare with the ages from Bradley Lake (odt format). The data files (odt format) also include code for the OxCal (version 4.4; https://c14.arch.ox.ac.uk/oxcal.html) Bayesian software models used with selected radiocarbon ages to calculate age probability density functions for the lake’s earthquake or tsunami-caused disturbance events, and for the stratigraphic contacts produced by earthquakes and tsunamis at 12 of the 13 tidal wetland sites (odt format). An additional text file (odt format) explains the addition of variance to the errors on laboratory reported radiocarbon ages in the tables analyzed prior to 1998, and those analyzed by the National Ocean Sciences AMS Facility (NOSAMS) at the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts. Data describing the results of our recent unsuccessful attempt to use optical dating methods (OSL and IRSL) on quartz grains from tsunami deposits in Bradley Lake to date the deposits can be found in Mahan et al. (2021; U.S. Geological Survey data release, https://doi.org/10.5066/P9YWIDOW).

This dataset consists of nine tables that include radiocarbon dates, Cesium-137 activity, grain size measurements, and scanning X-ray fluorescence element intensity counts.

This dataset consists of nine tables that include radiocarbon dates, Cesium-137 activity, grain size measurements, and scanning X-ray fluorescence element intensity counts.

The USGS Powell Center Cascadia earthquake hazards working group compiled published onshore and offshore paleoseismic data along the Cascadia subduction zone, spanning sites from Vancouver Island to the Mendocino triple junction. Evidence for megathrust rupture includes coastal land-level change, tsunami inundation, onshore shaking proxies such as landslides or liquefaction, and offshore shaking proxies such as marine turbidites. The quality of paleoseismic data for megathrust rupture along the Cascadia subduction zone collected over the past three decades varies because analytical capabilities and data collection methodologies have evolved. Thus, as part of the compilation, we also present a ranking scheme to assess the quality of age estimates and evidence for great megathrust rupture. With the age ranking scheme, we ask: "How well is a proposed paleoseismic event dated?" based on the materials and methods used. With the evidence ranking scheme, we ask: "How confident are we that a proposed event is, in fact, the result of a Cascadia megathrust rupture?" based on the sedimentological characteristics, correlation, and mapping. The evidence ranking scheme also helps to evaluate possible alternative mechanisms for creating paleoseismic evidence such as crustal fault, intraslab, or distant tsunamigenic earthquake.

The USGS Powell Center Cascadia earthquake hazards working group compiled published onshore and offshore paleoseismic data along the Cascadia subduction zone, spanning sites from Vancouver Island to the Mendocino triple junction. Evidence for megathrust rupture includes coastal land-level change, tsunami inundation, onshore shaking proxies such as landslides or liquefaction, and offshore shaking proxies such as marine turbidites. The quality of paleoseismic data for megathrust rupture along the Cascadia subduction zone collected over the past three decades varies because analytical capabilities and data collection methodologies have evolved. Thus, as part of the compilation, we also present a ranking scheme to assess the quality of age estimates and evidence for great megathrust rupture. With the age ranking scheme, we ask: "How well is a proposed paleoseismic event dated?" based on the materials and methods used. With the evidence ranking scheme, we ask: "How confident are we that a proposed event is, in fact, the result of a Cascadia megathrust rupture?" based on the sedimentological characteristics, correlation, and mapping. The evidence ranking scheme also helps to evaluate possible alternative mechanisms for creating paleoseismic evidence such as crustal fault, intraslab, or distant tsunamigenic earthquake.

Observations of widespread liquefaction and stratigraphic and structural relationships in a trench across an ambiguous scarp are used to constrain the timing of Holocene earthquakes on the northwest-striking Wallula fault zone in southeast Washington and Oregon. Additional observations and age constraints from OSL analysis of samples collected from large-scale liquefaction features that crosscut the Mount St Helens J tephra (13.8-13.7 ka) exposed at a nearby outcrop suggest up to 3 Holocene regional liquefaction events, any of which were likely triggered by seismic shaking sourced from either the Wallula fault and/or faults of the Yakima fold and thrust belt. Our observations provide plausible evidence supporting that the scarp formed during the M6 1936 Milton-Freewater earthquake. In addition, stratigraphic relationships observed in this study indicate that the end of the Missoula Floods in the southeast Washington region occurred sometime between 13.8–13.5 cal. k.y. B.P., approximately 1,000 years earlier than prior estimates.

Observations of widespread liquefaction and stratigraphic and structural relationships in a trench across an ambiguous scarp are used to constrain the timing of Holocene earthquakes on the northwest-striking Wallula fault zone in southeast Washington and Oregon. Additional observations and age constraints from OSL analysis of samples collected from large-scale liquefaction features that crosscut the Mount St Helens J tephra (13.8-13.7 ka) exposed at a nearby outcrop suggest up to 3 Holocene regional liquefaction events, any of which were likely triggered by seismic shaking sourced from either the Wallula fault and/or faults of the Yakima fold and thrust belt. Our observations provide plausible evidence supporting that the scarp formed during the M6 1936 Milton-Freewater earthquake. In addition, stratigraphic relationships observed in this study indicate that the end of the Missoula Floods in the southeast Washington region occurred sometime between 13.8–13.5 cal. k.y. B.P., approximately 1,000 years earlier than prior estimates.

This dataset includes raw and processed, high-resolution seismic-reflection data collected in 2010 to collect information on active offshore faults. The survey area is offshore southern California between Oceanside and La Jolla. The data were collected aboard the U.S. Geological Survey R/V Parke Snavely. The seismic-reflection data were acquired using a SIG 2mille minisparker. Subbottom acoustic penetration spanned tens to several hundreds of meters, variable by location.