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Whats New

Upcoming Talks, New Papers and Other Things

Short Course in Subaqueous Paleoseismology offered at thte Geological Society of America Meeting in Seattle

The course is offered Saturday October 21. See GSA for details and registration.

http://community.geosociety.org/gsa2017/science-careers/courses

New Paper Released!

This paper takes a close look a the Northern San Andreas Fault structure, evolution and termination in Northern California

Beeson, J.W., Goldfinger, C., Johnson, S.Y., 2017, The Offshore Section of the Northern San Andreas Fault: Fault Zone Geometries, Shallow Deformation Patterns, and Asymmetric Basin Growth, Geosphere, v13 (3)

New Paper Released!

This paper models seafloor habitat using Bayesian methods

Havron, A., Goldfinger, C., Henkel, S., Marcot, B.G., Romsos, C., Gilbane, L., 2017, Mapping marine habitat suitability and uncertainty using Bayesian networks: a case study of northeastern Pacific benthic macrofauna, Ecosphere, v. 8 (7), p. 1-25.

New Paper Released!

A new paper came out this week that attempts to integrate tsunami models, onshore andoffshore paleoseismic data in Southern Cascadia:

George R. Priest, Robert C. Witter, Y. Joseph Zhang, Chris Goldfinger, Kelin Wang, Jonathan C. Allan, 2017, New constraints on coseismic slip during southern Cascadia subduction zone earthquakes over the past 4,600 years implied by tsunami deposits and marine turbidites, Natural Hazards DOI: 10.1007/s11069-017-2864-9 http://activetectonics.coas.oregonstate.edu/paper_files/Priest%20et%20al.%202017%20offprint.pdf

 

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

   

 

 

Transverse Faulting of the Cascadia Submarine Forearc

 

Background

In 1992 we began investigating the serendipitous discovery of unusual transverse strike slip faults along the Cascadia margin using sidescan sonar, multichannel seismic reflection profiles, and submersible observations.

Summary of Results

Using sidescan sonar, seismic reflection profiles, and swath bathymetric data we have mapped  a set of WNW-trending left-lateral strike-slip faults that deform the Oregon and Washington submarine forearc.  Evidence for left-lateral separation includes offset of accretionary wedge folds, channels, and other surficial features; sigmoidal left bending of accretionary wedge folds, and offset of abyssal plain sedimentary units.  Five of these faults cross the plate boundary, extending 5-21 km into the Juan de Fuca plate. 

 

Using offset of subsurface piercing points, and offset of approximately dated submarine channels, we calculate slip rates for these five faults of 5.5 to 8.5 mm/yr.  Little or no offset of these faults by the basal thrust of the accretionary wedge is observed.  Holocene offset of submarine channels and unconsolidated sediments is observed in sidescan records and directly by submersible. The strike-slip faults are most likely driven by dextral shearing of the subducting slab and propagate upward through the overlying accretionary wedge. Tangential hydrodynamic drag caused by obliqueinsertion of the slab into the mantle is a possible driving mechanism.

 

Cascadia subduction zone transverse strike-slip faulting, North Nitinat fault sidescan

Figure 1. SeaMarc 1A sidescan mosaic of the North Nitinat Fault (NNF) on the bayssal plain off the Washington margin. The Sinistral NNF can be seen offsetting a channel at center right, and hosts a mud volcano at center leftwhich is also offset by the fault. (click for larger image)

 

Four sinistral faults observed in only the upper plate may be remanent traces of previous basement-driven deformation. Alternatively, a similar, though unrelated dextral shear couple driven by interplate coupling may drive these faults, and may augment deformation of the upper plate for all the sinistral faults. A model of overall right-lateral simple shear of the submarine forearc is consistent with the observed surface faults, which may be R' or antithetic shears to the overall right-shear couple.  The major strike-slip faults define elongate blocks that, because of their orientation and sinistral slip direction, must rotate clockwise.  We infer that the deformation of the submarine forearc (defined to include the lower plate) is highly strain-partitioned into arc-normal shortening, and arc-parallel strike-slip and translation.  The high slip rates of the strike-slip faults, coupled with the lack of offset of these faults as they cross the plate boundary, imply that the seaward accretionary wedge is not moving at the expected convergence rate relative to the subducting plate. We conclude that the accretionary wedge is rotating and translating northward, driven by the tangential component of Juan de Fuca - North American plate convergence.

 

Cascadia subduction zone transverse strike-slip faulting, Wwecoma, daisy bank, Alvin Canyon faults seismic reflection

Figure 2. North-South MCS profile on the abyssal plain, just seaward of the deformation fron at ~ 45 N. Profile panels A-C show crossings of the Wecoma, Daisy Bank, and Alvin Canyon faults respectively. Profiles show offset of oceanic crust (OC), and flower structures and pop-ups associated with the northern two faults.

Cascadia subduction zone transverse strike-slip faulting, Wecoma fault slip rate block diagram

Figure 3. Block diagram showing restoration of net slip based on seaward tapering stratigraphic units. Net offset was determined from the reflection profiles, and age control of the units via stratigraphic linkage to ODP site 174.

 

We used the geometry of trench fill sediment wedges to determine net offset of the faults. If the geometry of the pre-faulting trenchward thickening wedges is simple, three profiles can define the wedge geometry sufficiently to use them as 3D piercing points, the offsets of which represents the net slip of the fault.  The three Oregon faults used many more profiles than did the Washington faults, which had the minimum number of profiles needed.  Reflection data indicate that the geometry of the wedges is simple and the layers that bound them are approximately planar over the distances involved.  Goldfinger et al. (1997a) also calculated the net slip of one fault (the Wecoma fault) using isopach plots of two subsurface units.  Using the wedge geometry captures total offset by the fault, which often is underestimated in measurements of offset isopachs due to drag folding and local velocity effects near the fault.  The five faults for which we used this technique have a vertical component of offset and show pronounced growth strata on the downthrown block, thus we were able to easily distinguish syn-faulting and pre-faulting units (Fig. 2).  We identified the point in the section at which interval thickness across the fault reversed from thicker on the downthrown block to thinner on the downthrown block.  Syn-faulting sedimentary units could not be used for this determination because the presence of growth strata invalidates the assumption that measured geometric changes on the profiles result from horizontal fault offset only.  In practice, we used two methods to determine fault slip.  For all five faults, we determined the wedge geometry from the seismic grid, then determined the fault offset required to produce the observed thickness change for two pre-faulting units.

We estimated the age of faulting by converting the two-way travel time to the base of the growth strata to depth in meters.  This conversion used an average velocity of 1680 m/s, calculated for the upper 400 m of the Nitinat Fan from ODP drilling and reflection data (Hyndman and Davis, 1992; Shipboard Scientific Party, 1994).  We derived fault age by using a net sedimentation rate of 100 cm/1000 yr for the Nitinat Fan calculated from the 1993 ODP drill sites (Shipboard Scientific Party, 1994) and  110 cm/1000 yr for the Astoria fan (Goldfinger et al., 1994; in press a) calculated using the thickness and age of the fan.  To establish the age of the Astoria Fan, we correlated a prominent seismic reflector at the base of the fan from the Wecoma fault to DSDP Site 174A.

Cascadia subduction zone transverse strike-slip faulting, Cascadia cutaway diagram, Daisy bank Fault

Figure 4. Cutaway schematic of the central Cascadia margin, showing surface traces of the Wecoma, Daisy Bank and Alvin Canyon Transverse faults. (Click for larger image)

 

Cascadia subduction zone transverse strike-slip faulting, Cascadia cutaway diagram, Daisy bank Fault

Figure 5. SeaMarc 1A sidescan mosaic of the Daisy bank Failt Zone on the upper slope off central Oregon. Sinistral motion and a left bend at center have opend a small pull-apart basin. drag folding with a sinistal motion sense visible at right. (click for larger image)

 

Cascadia subduction zone transverse strike-slip faulting, Cascadia cutaway diagram, Daisy bank FaultCascadia subduction zone transverse strike-slip faulting, Cascadia cutaway diagram, Daisy bank FaultCascadia subduction zone transverse strike-slip faulting, Cascadia cutaway diagram, Daisy bank Fault

Figure 6. video frames of transect along the Daisy bank Fault on the upper slope of Oregon. This dive used the DELTA submersible, and crossed the fautl at the extreme eastern end of the sidescan mosaic shown in Figure 5.

 

 

Figure 7. Video from the submersible SeaCliff at the scarp of the Thomson Ridge Fault near its intersection with the Cascadia deformation front.

 

Daisy Bank, on the upper continental slope, is one of several uplifted Neogene structural highs off Oregon (Kulm and Fowler, 1974).  The DBF bounds the southern flank of Daisy Bank; a second less prominent strand of the fault bounds the northern flank.  SeaMARC 1A sidescan imagery, and multichannel (MCS) and single channel (SCS) seismic reflection data, show that the Daisy Bank fault is a wide structural zone, within which Daisy Bank is uplifted as a horst between two strands of the main fault.  The main fault zone is 5-6 km wide northwest of Daisy Bank, widening around the oblong bank, then narrowing to a single strand to the southeast.  The traces of the fault strands are straight, implying a near vertical fault.  Probable drag folds of exposed strata, with a left-lateral sense of motion, are visible in sidescan imagery southeast of the bank (Fig. 12).  Mapping from seismic reflection profiles indicates left-lateral offsets of NNW-trending accretionary wedge fold axes at Daisy Bank (Fig. 5).  Scarp heights measured from the DELTA submersible range from tens of centimeters to 47 m.  The net uplift of the southern flank of Daisy Bank by both folding and faulting is about 130 m.  From DELTA, we traced one of the Daisy Bank scarps into an area of low relief and mud deposition.  We observed a fresh scarp striking 290° across the unconsolidated Holocene mud (Figure 6), which is visible in the AMS 150 kHz sidescan images (Fig. 5).  Stratigraphic relationships indicate post 12 ka motion on this segment of the Daisy Bank fault (Goldfinger et al., 1997).  

 

Cascadia subduction zone transverse strike-slip faulting, Cascadia fault map

Figure 7. Structure map of the Cascadia margin, showing transverse fault locations.

 

 

Conclusions
                Using sidescan sonar, seismic reflection profiles, and swath bathymetric data we have mapped  a set of WNW-trending left-lateral strike-slip faults that deform the Oregon and Washington submarine forearc.  Evidence for left-lateral separation includes offset of accretionary wedge folds, channels, and other surficial features; sigmoidal left bending of accretionary wedge folds, and offset of abyssal plain sedimentary units.  Five of these faults cross the plate boundary, extending 5-21 km into the Juan de Fuca plate.  Using offset of subsurface piercing points, and offset of approximately dated submarine channels, we calculate slip rates for these five faults of 5.5 to 8.5 mm/yr.  Little or no offset of these faults by the basal thrust of the accretionary wedge is observed.  Holocene offset of submarine channels and unconsolidated sediments is observed in sidescan records and directly by submersible.

The strike-slip faults are most likely driven by dextral shearing of the subducting slab and propagate upward through the overlying accretionary wedge.  Tangential hydrodynamic drag caused by oblique insertion of the slab into the mantle is a possible driving mechanism.  Four sinistral faults observed in only the upper plate may be remanent traces of previous basement-driven deformation.  Alternatively,  a similar, though unrelated dextral shear couple driven by interplate coupling may drive these faults, and may augment deformation of the upper plate for all the sinistral faults. 

A model of overall right-lateral simple shear of the submarine forearc is consistent with the observed surface faults, which may be R' or antithetic shears to the overall right-shear couple.  The major strike-slip faults define elongate blocks that, because of their orientation and sinistral slip direction, must rotate clockwise.  We infer that the deformation of the submarine forearc (defined to include the lower plate) is highly strain-partitioned into arc-normal shortening, and arc-parallel strike-slip and translation.  The high slip rates of the strike-slip faults, coupled with the lack of offset of these faults as they cross the plate boundary, imply that the seaward accretionary wedge is not moving at the expected convergence rate relative to the subducting plate.  We conclude that the accretionary wedge is rotating and translating northward, driven by the tangential component of Juan de Fuca - North American plate convergence.  

 

 

Methods Summary

  
Data Acquisition and Processing
High-resolution sidescan sonar data were collected with a deep-towed SeaMARC 1A 30-kHz system capable of imaging a 2-km or a 5-km swath width with spatial resolutions of 1 and 2.5 m, respectively.   An Alpha Marine Systems (AMS) 150 kHz system was used to collect sidescan data on the continental shelves of Oregon and Washington, with a 1 km swath width and 0.5 m resolution.  Approximate coverage of these surveys is shown in Figure 1.  All sidescan data were located using GPS, then processed using OSU's Sonar deep-tow sidescan processing system.  Processing included towfish positioning, geometric and speed corrections, correction for towfish attitude, georeferencing of image pixels to a latitude-longitude grid, histogram equalization, and image enhancement.  The final imagery was then integrated with other data layers in a raster/vector Geographical Information System (GIS) for analysis. 


Regional sidescan data (EEZ-SCAN 84 Scientific Staff, 1986) using the Geologic LOng Range Inclined Asdic (GLORIA) shallow-towed system were also used in interpretation of margin structure.  The GLORIA imagery was georeferenced to Hydrosweep bathymetry collected by us in Washington (1993), or existing NOAA SeaBeam bathymetry in Oregon in order to produce a consistent spatial dataset.


In our structural interpretations we have used about 30,000 km of seismic-reflection profiles collected by academic institutions, the U.S. Geological Survey, NOAA, and the petroleum industry (Goldfinger et al., 1992a).  The seismic-reflection profiles vary widely in quality, depth of penetration and navigation accuracy, and range from single-channel sparker records navigated with Loran A to 144-channel digital profiles navigated with GPS.  An important dataset is a multichannel seismic survey conducted off central Oregon in 1989 (MacKay et al., 1992).  Approximately 2000 km of NAVSTAR-navigated 144-channel reflection profiles were collected and processed through time migration at the University of Hawaii.  Three of the Oregon strike-slip faults intersect the deformation front within this survey (Fig. 2), allowing detailed structural analysis, as well as determination of fault slip rates. 

 

Acknowledgments
We thank the crews of the research vessels Thomas Thompson (University of Washington), and support vessels Cavalier and Jolly Roger;  DELTA pilots Rich and Dave Slater, Chris Ijames, and Don Tondrow; members of the Scientific Party on cruises from 1992-1993 during which most of the data were collected; Kevin Redman, David Wilson, Tim McGiness, Wolf Krieger, Chris Center, Kirk O'Donnell from Williamson and Associates of Seattle Washington, our sidescan contractors; Ed Llewellyn for co-writing Sonar, OSU's sidescan-sonar processing software; Chris Fox, and Steve Mutula of NOAA for their assistance with the multibeam data.  Multibeam bathymetry data was collected by NOAA and processed by the NOAA Pacific Marine and Environmental Laboratory, Newport OR.  Thanks to Chris Fox and Bob Dziak, also of NOAA Newport, OR for the T-wave earthquake locations shown in Fig. 2.  We thank Eric Geist, Roger Bilham, and Greg Moore for thorough and helpful reviews.  This research was supported by National Science Foundation grants OCE-8812731 and OCE-9216880; U.S. Geological Survey National Earthquake Hazards Reduction Program awards 14-08-0001-G1800, 1434-93-G-2319, and 1434-93-G-2489, and the NOAA Undersea Research Program at the West Coast National Undersea Research at the University of Alaska grants UAF-92-0061 and UAF-93-0035.

 

Publications

Appelgate, B., Goldfinger, C., Kulm, L.D., MacKay, M., Fox, C.G., Embley, R.W., and Meis, P.J., 1992, A left lateral strike slip fault seaward of the central Oregon convergent margin: Tectonics, v. 11, p. 465-477.

Goldfinger, C., Kulm, L.D., and Yeats, R.S., 1992, Neotectonic map of the Oregon continental margin and adjacent abyssal plain: Portland, Oregon Department of Geology and Mineral Industries Open-File Report O-92-4, scale 1:500,000 Arc Shapefiles

Goldfinger, C., Kulm, L.D., Yeats, R.S., Appelgate, B., MacKay, M., and Moore, G.F., 1992, Transverse structural trends along the Oregon convergent margin: implications for Cascadia earthquake potential: Geology,  v. 20, p. 141-144. 

Goldfinger, C., Kulm, L.D., Yeats, R.S., Hummon, C., Huftile, G.J., Niem, A.R., Fox, C.G., and McNeill, L.C., 1996, Oblique strike-slip faulting of the Cascadia submarine forearc:  The Daisy Bank fault zone off central Oregon, in Bebout, G.E., Scholl, D., Kirby, S., and Platt, J.P., eds., Subduction top to bottom, AGU Geophysical Monograph 96, Washington, D. C., American Geophysical Union, p. 65-74.

Goldfinger, C., Kulm, L.D., Yeats, R.S., Appelgate, B., MacKay, M., and Cochrane, G.R., 1996, Active strike-slip faulting and folding of the Cascadia plate boundary and forearc in central and northern Oregon, in Rogers, A.M., Walsh, T.J., Kockelman, W.J., and Priest, G., eds., Assessing and reducing earthquake hazards in the Pacific Northwest, Volume I,  U.S.G.S. Professional Paper 1560, U.S. Geological Survey.

Goldfinger, C., Kulm, L.D., Yeats, R.S., McNeill, L.C., and Hummon, C., 1997, Oblique strike-slip faulting of the central Cascadia submarine forearc: Journal of Geophysical Research,  v. 102,  p. 8217-8243. 

McCaffrey, R., and Goldfinger, C., 1995, Forearc deformation and great earthquakes: Implications for Cascadia earthquake potential: Science, v. 267, p. 856-859.