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The story of a Yakima fold and how it informs Late Neogene and Quaternary backarc deformation in the Cascadia subduction zone, Manastash anticline, Washington, USA

The Yakima folds of central Washington, USA, are prominent anticlines that are the primary tectonic features of the backarc of the northern Cascadia subduction zone. What accounts for their topographic expression and how much strain do they accommodate and over what time period? We investigate Manastash anticline, a north vergent fault propagation fold typical of structures in the fold province. F
Authors
Harvey M. Kelsey, Tyler C. Ladinsky, Lydia M. Staisch, Brian L. Sherrod, Richard J. Blakely, Thomas Pratt, William Stephenson, Jackson K. Odum, Elmira Wan

3-D simulations of M9 earthquakes on the Cascadia Megathrust: Key parameters and uncertainty

Geologic and historical records indicate that the Cascadia subduction zone is capable of generating large, megathrust earthquakes up to magnitude 9. The last great Cascadia earthquake occurred in 1700, and thus there is no direct measure on the intensity of ground shaking or specific rupture parameters from seismic recordings. We use 3-D numerical simulations to generate broadband (0-10 Hz) synthe
Authors
Erin Wirth, Arthur Frankel, John Vidale, Nasser A. Marafi, William J. Stephenson

Evaluating a kinematic method for generating broadband ground motions for great subduction zone earthquakes: Application to the 2003 Mw 8.3 Tokachi‐Oki earthquake

We compare broadband synthetic seismograms with recordings of the 2003 MwMw 8.3 Tokachi‐Oki earthquake to evaluate a compound rupture model, in which slip on the fault consists of multiple high‐stress‐drop asperities superimposed on a background slip distribution with longer rise times. Low‐frequency synthetics (<1  Hz<1  Hz) are calculated using deterministic, 3D finite‐difference simulations and
Authors
Erin A. Wirth, Arthur Frankel, John E. Vidale

Integrated geophysical characteristics of the 2015 Illapel, Chile, earthquake

On 16 September 2015, a Mw 8.3 earthquake ruptured the subduction zone offshore of Illapel, Chile, generating an aftershock sequence with 14 Mw 6.0–7.0 events. A double source W phase moment tensor inversion consists of a Mw 7.2 subevent and the main Mw 8.2 phase. We determine two slip models for the mainshock, one using teleseismic broadband waveforms and the other using static GPS and InSAR surf
Authors
Matthew W. Herman, Jennifer Nealy, William L. Yeck, William D. Barnhart, Gavin P. Hayes, Kevin P. Furlong, Harley M. Benz

Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey

The Cascade Range in central Oregon has been shaped by tectonics, volcanism, and hydrology, as well as geomorphic forces that include glaciations. As a result of the rich interplay between these forces, mafic volcanism here can have surprising manifestations, which include relatively large tephra footprints and extensive lava flows, as well as water shortages, transportation and agricultural disru
Authors
Natalia I. Deligne, Daniele Mckay, Richard M. Conrey, Gordon E. Grant, Emily R. Johnson, Jim O'Connor, Kristin Sweeney

Modified mercalli intensities for nine earthquakes in central and western Washington between 1989 and 1999

We determine Modified Mercalli (Seismic) Intensities (MMI) for nine onshore earthquakes of magnitude 4.5 and larger that occurred in central and western Washington between 1989 and 1999, on the basis of effects reported in postal questionnaires, the press, and professional collaborators. The earthquakes studied include four earthquakes of M5 and larger: the M5.0 Deming earthquake of April 13, 1990
Authors
Thomas M. Brocher, James W. Dewey, John F. Cassidy

New constraints on coseismic slip during southern Cascadia subduction zone earthquakes over the past 4600 years implied by tsunami deposits and marine turbidites

Forecasting earthquake and tsunami hazards along the southern Cascadia subduction zone is complicated by uncertainties in the amount of megathrust fault slip during past ruptures. Here, we estimate slip on hypothetical ruptures of the southern part of the megathrust through comparisons of late Holocene Cascadia earthquake histories derived from tsunami deposits on land and marine turbidites offsho
Authors
George R. Priest, Robert C. Witter, Yinglong J. Zhang, Chris Goldfinger, Kelin Wang, Jonathan C. Allan

Effects of deep basins on structural collapse during large subduction earthquakes

Deep sedimentary basins are known to increase the intensity of ground motions, but this effect is implicitly considered in seismic hazard maps used in U.S. building codes. The basin amplification of ground motions from subduction earthquakes is particularly important in the Pacific Northwest, where the hazard at long periods is dominated by such earthquakes. This paper evaluates the effects of bas
Authors
Nasser A. Marafi, Marc O. Eberhard, Jeffrey W. Berman, Erin A. Wirth, Arthur Frankel

Noble gas data from Goldfield and Tonopah epithermal Au-Ag deposits, ancestral Cascades Arc, USA: Evidence for a primitive mantle volatile source

The He, Ne, and Ar isotopic composition of fluid inclusions in ore and gangue minerals were analyzed to determine the source of volatiles in the high-grade Goldfield and Tonopah epithermal Au-Ag deposits in southwestern Nevada, USA. Ar and Ne are mainly atmospheric, whereas He has only a minor atmospheric component. Corrected 3He/4He ratios (with atmospheric He removed) range widely from 0.05 to 3
Authors
Andrew H. Manning, Albert H. Hofstra

Alternative rupture-scaling relationships for subduction interface and other offshore environments

Alternative fault-rupture-scaling relationships are developed for Mw 7.1– 9.5 subduction interface earthquakes using a new database of consistently derived finitefault rupture models from teleseismic inversion. Scaling relationships are derived for rupture area, rupture length, rupture width, maximum slip, and average slip. These relationships apply width saturation for large-magnitude interface e
Authors
Trevor Allen, Gavin P. Hayes

Microfossil measures of rapid sea-level rise: Timing of response of two microfossil groups to a sudden tidal-flooding experiment in Cascadia

Comparisons of pre-earthquake and post-earthquake microfossils in tidal sequences are accurate means to measure coastal subsidence during past subduction earthquakes, but the amount of subsidence is uncertain, because the response times of fossil taxa to coseismic relative sea-level (RSL) rise are unknown. We measured the response of diatoms and foraminifera to restoration of a salt marsh in south
Authors
B. P. Horton, Yvonne Milker, T. Dura, Kelin Wang, W.T. Bridgeland, Laura S. Brophy, M. Ewald, Nicole Khan, S.E. Engelhart, Alan R. Nelson, Robert C. Witter

Sediment gravity flows triggered by remotely generated earthquake waves

Recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the Cascadia Subduction Zone of the Pacific Northwest. We analyzed seafloor temperature, pressure, and seismic signals, and video stills of sediment-enveloped instruments recorded during the 2011–2015 Cascadia Initiative experiment, and seafloor morphology. Our r
Authors
H. Paul Johnson, Joan S. Gomberg, Susan Hautala, Marie Salmi