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Upcoming Talks and Other Things

National Academy of Science, Engineering and Medicine

Joint BESR/COSG Meeting - The Cascadia Subduction Zone: Science, Impacts, and Response

November 10-11, 2016, National Academy of Sciences Building
2101 Constitution Ave NW Washington DC 20418

 

City Club Earthquake Forum, Kells Pub Portland, November 1, 5:30 pm

 

Goldfinger Active Tectonics Lab wins 2016 Geological Society of America Kirk Bryan Award.

 

TEdx Mt. HoodTEDx Portland, June 18, 2016. Revolution Hall

 

 

Science Pub Corvallis "Shaking up the Northwest, the Cascadia Earthquake in our Future" Majestic Theatre, Covallis 6 pm. Science Pub at The Majestic @ The Majestic Theatre | Corvallis | Oregon | United States

 

New Yorker Festival, Manhattan, October 3, School of Visual Arts, Theatre 1, 10 am. App_icon

NWEA Workshop, Hood River Inn, October 2.

Oregon Coast Economic Summit, August 27, Grand Ronde.

The Really Big One: A Public Forum On Earthquake Hazards

and Preparedness in the PNW, University of Oregon, Eugene, August 6, 7 PM. 156 Straub Hall.

New Books

New Novel: Stick Slip from Chris Scholz! An entertaining read about a Cascadia great earthquake.

The Next Tsunami examines our short term memory about disasters, Los Angeles Times, March 21, 2014

New Papers

Second Paper detailing the marine paleoseismic record of the Northern Sumatra margin released.

Second New Canadian Study Corroborates and Extends Cascadia Marine Paleoseismic Record

New Thesis Released: Southern Cascadia Turbidites Traced with High-Resolution CHIRP Sub Bottom Profiles.

New Dissertation Released: Sumatra Paleoseismology

New Paper Released: Cascadia Segmented Rupture Tsunami Models

New Paper Released: Cascadia Tsunami Models

New Paper Released: Cascadia Great Earthquake Clustering

Coastwide Tsunami inundation Scenarios for Oregon Released

"Superquakes and Supercycles" released, Seismological Research Letters

New Paper Released: Cascadia Turbidites in Forearc Lakes?

Preliminary study of existing lake sedimentary records suggests a record of great earthquakes.

New Cascadia Paper Released: Segmented Ruptures Along the Southern Cascadia Margin

New core and high resolution reflection data illuminate thesouthern Cascadia paleoseismic record.

New Canadian Study Corroborates Cascadia Marine Paleoseismic Record

Seismically generated turbidites in Effingham Inlet, western Vancouver Island.

Second in Sumatra Paleoseismology Series Released

Other Stuff

Bayesian Spatial Analysis Team Wins Department of the Interior Partners in Conservation Award

Oregon Earthquake Resiliency Report Released

Oregon Tsunami Work Wins Award

Successful geophysical cruise aboard the Derek. M. Baylis completed with very low carbon footprint

Cascadia, the Movie! Animation of 10,000 year earthquake record from marine and coastal paleoseismic sites.

Initiative to Retrofit Schools in Portand for Earthquakes

   

 

 

Deformation Styles and Rates Based on Deformed Low-Stand Shorelines

 

Investigators

Chris Goldfinger, L.D. Kulm, R.S. Yeats, J.D. Chaytor

 

Abstract

 

 The outer arc high of the Cascadia submarine forearc is strongly heterogeneous, with discrete banks that are sites of greater long term uplift and deformation than interbank areas along strike.  Multibeam bathymetry, deep-towed sidescan sonar data and submersible observations reveal submerged shorelines rimming the three major submarine banks on the outer continental shelf of Oregon.  Evidence that the observed features are submerged shorelines includes a smooth sand platform terminating in an abrupt step up to a shallower rough surface of exposed rock.  We interpret these as and abrasion platform, seacliff, and subaerially eroded geologic landscape.  High resolution sidescan sonar and DELTA submersible observations reveal spectacular shoreline features, including barrier islands, estuaries, and headlands. The preservation of these ephemeral features attests to the very rapid rise of sea level at the close of the Pleistocene. Submarine traverses found Pholad borings, oxidized cross stratified sands, and shallow-water fossil debris at the base of former beach cliffs.  One dated intertidal fossil is consstent with abandonment of the Heceta Bank shoreline following the last glacial maximum.  Shoreline angles were originally horizontal and close to sea level, but are now warped and faulted.  One of the major submarine banks, Heceta Bank, has subsided and tilted to the south and west.  Nehalem Bank has been deformed by complex interplay of listric normal faulting and margin-normal compression.  Coquille Bank appears relatively undeformed.  Although Heceta Bank has undergone ~1 km of uplift since the Miocene, net subsidence has occurred during the latest Quaternary.  This could reflect a relationship to adjacent submarine slides, or a significant change in margin tectonics from tectonic underplating to tectonic erosion. 
The intense deformation, and long-term uplift of the banks suggests greater basal shear stress beneath the banks as compared with interbank areas. This appears to be expressed by numerous landward dipping thrusts underlying the banks.   This deformation continues today, as indicated by deformation of the low-stand shorelines.  These data suggest that stronger plate coupling may occur beneath the banks, and thus they may represent asperities along the coupled interface. 

Introduction

Modern rates of active deformation have thus far been based mainly on the tectonic geomorphology of subaerial landforms. However, the world's principal plate boundaries are mostly located offshore, making such studies difficult at many active continental margins. However, sidescan sonar, swath bathymetry, high-resolution seismic reflection profiling, and submersible observations allow the mapping of deformed stream channels, abrasion platforms, and submerged lowstand shorelines, leading to the determination of deformation rates. We have previously used sidescan sonar imagery, seismic reflection profiles, and dated piston cores to determine Holocene slip rates of several left-lateral strike-slip faults on the Juan de Fuca (JDF) plate, immediately west of the Cascadia deformation front off Oregon and Washington. These faults offset the baseof-slope channel; their slip rates are determined from offset isopachs of landward thickening Pleistocene submarine fan deposits, and from surficial offset of dated channels. Recently, we have discovered a late Pleistocene lowstand shoreline rimming three major submarine banks along the outer shelf off Oregon.


Cascadia submerged shorelines, intertidal organisms In 1993-95, we investigated this shoreline with AMS 150 kHz sidescan sonar and the DELTA submersible and found spectacular shoreline features, including barrier islands, estuaries, and headlands. The preservation of these ephemeral features attests to the very rapid rise of sealevel at the close of the Pleistocene. Submarine traverses found pholad borings, oxidized cross stratified sands, and shallow-water fossil debris at the base of beach cliffs. We also conducted sidescan and submersible traverses across Nehalem and Coquille banks and found similar features. Coquille Bank, in fact, was formerly an island. Datable intertidal fossils like the barnacles at right indicate the age of last submergence of the latest glacial shoreling at 14-18 ka.


Shoreline angles were originally horizontal and close to sea level. Now these shoreline angles are warped and faulted, locally to depths of 200-300 m, deeper than the Wisconsin lowstand of -120 m, indicating that the shoreline angles reflect vertical tectonics rather than eustatic sea level change. Two of the major submarine banks, Heceta and Nehalem, are strongly tilted to the south (margin parallel), and deformed by faults and folds, while the third appears relatively undeformed. The submerged shoreline is at about the depth of the lowstand at the north ends of these two blocks, while the south ends are deeper, indicating overall subsidence of these blocks. Both banks are known to have been uplifted approximately 1 km since the Miocene, so the recent subsidence could reflect one of many vertical fluctuations, or a significant change in margin tectonics. Subsidence of the banks may be due to gravitational collapse or tectonic erosion of the margin, despite the presence of an accreting prism of sediments to the west.


The deformation of the outer shelf is on a much longer time-scale than moderd geodetic techniques, but can be compared to uplift rates onshore determined with geodetic techniques and tide gauges, as well as deformation of marine terraces to gain insight into the processes and rates over a range of time scales. We hope these data will help us to identify along-strike variability that may indicate segmentation of the Cascadia plate boundary.

 

Cascadia Deformed Shorelines

Cascadia submerged shorelines, intertidal organisms, bathymetric image

Figure 2. Color shaded relief image of Heceta Bank, Oregon looking to the southeast. EM-300 multibeam data collected by MBARI and NOAA PMEL/Newport. Rough bank top is exposed Miocene strata. Note smooth wave-cut platform surrounding the bank at a depth of 100-150 m.

 

 

 

 

 

 

 

 

 

 

 

 

Cascadia submerged shorelines, intertidal organisms, shoreline features

 

Figure 3. AMS-150 sidescan sonar mosaic of the late Pleistocene low-stand shoreline and wave-cut platform at Heceta Bank, Oregon continental shelf. Visible in the mosaic are the smooth, low-reflectivity abrasion platform at left; the high reflectivity bedrock outcrops at right; and the paleo-seacliff separating these regions. At center, a paleo stream/river entered the sea at a small estuary. The former stream channel has evidence of unidirectional current indicators as observed directly from teh DELTA submersible. Other peripheral nearshore features such as tombolos and offshore bars (not shown) were surprisingly well preserved. Intertidal rock boring Pholad clams and mussels were recovered from the low seacliff.

 

 

 

 

 

 

 

 

 

 

 

 

Cascadia submerged shorelines, intertidal organisms, shoreline features

 

 

 

 

 

 

 

 

 

Figure 4. AMS-150 sidescan sonar image of a former sea-stack on the northern Oregon continental shelf at Nehalem Bank. The top of the stack was eroded at a previous abrasion platrom level, then later was awash at this site at a water depth of 140 m. Coarser high-backscatter gravel, likely derived from the stack, is the high backscatter material surrounding the stack. Swath width of image is 1000m.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Publications

Chaytor, J. D., Chris Goldfinger, C., Meiner, M. A., Huftile, G. J., Romsos, C. G., and Legg, M. R., 2008, Measuring Vertical Tectonic Motion at the Intersection of the Santa Cruz-Catalina Ridge and Northern Channel Islands Platform, California Continental Borderland, Using Submerged Paleoshorelines, Bulletin of the Geological Society of America, v. 120. P. 1053-1071.chaytor shorelines

Goldfinger, C., Kulm, L.D., McNeill, L., Yeats, R.S., Hummon, C., Huftile, G., Schneider, C., Neim, A.R., Tsutsumi, H., and Chen, Y.J., 1994, Cascadia subduction zone: Active deformation of the Oregon continental shelf: Oregon Academy of Sciences, Proceedings, v. XXX, p. 38.

 

Acknowledgements

We thank Kevin Redman and many other colleagues at Williamson and Associates for collection of the AMS 150 sidescan data.  We thank DELTA pilots David and Rich Slater, and Chris Ijames, ROPOS pilots Kieth XX and Kieth XXX, and the officers and crews of the Thomas G. Thompson from 2000-2005.  We thank LaVerne Kulm, Lisa McNeill, Roland Bergmann, Roland von Heune, Lisa McNeill, Kerry Sieh, Ray Wells, Kelin Wang, Alan Niem, and Yuichi Sugiyama for discussion of these issues over the years.  Thanks to Alan Mix for use of his sealevel compilation.