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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 shows evedence of offshore erosion caused during the cataclysmic Missoula flood events.

Beeson, J.W., Goldfinger, C., and Fortin, W.F., 2017, Large-scale modification of submarine geomorphic features on the Cascadia accretionary wedge caused by catastrophic flooding events:
Geosphere, v. 13, no. 4, p. 1–16, doi:10.1130/GES01388.1.

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

   

 

 

Forearc Deformation Based on Deformation of Regional Unconformities

 

Investigators

Lisa C. McNeill, Chris Goldfinger, Robert S. Yeats, Laverne D. Kulm, Katrina Peterson, and Charles Hutto

 

Summary

        Seismic reflection profiles, industry well logs, and seafloor samples were used to construct structure contours of a late Miocene-early
Pliocene unconformity on the Oregon continental shelf and upper slope, outlining a deformed elongate forearc basin.  The unconformity is probably 6-7.5 Ma, a worldwide hiatus found at northeast Pacific ODP sites.  The unconformity is angular and probably subaerial on much of the middle to inner shelf, and could be traced farther seaward as a continuous reflector where it may be conformable or disconformable.  Depths to the unconformity are up to 2.5 km, with thick Eocene to late Miocene strata below.  The current seaward edge of the basin forms a N-S-trending outer-arc high, but the basin may have formerly extended farther seaward.  The outer-arc high prevented the bypassing of sediment onto the accretionary wedge and abyssal plain.  The unconformity is deformed by active shelf structures, including late Pliocene-Pleistocene submarine banks which control the position of the shelf edge, and active faults including Daisy Bank and Nehalem Bank faults. The active Stonewall Bank anticline isolates a former remanent of the basin, the Newport syncline.  The landward boundary of the basin is the uplifted Coast Range, but prior to late Miocene uplift, the basin extended farther east.  Coast Range uplift caused the basin axis to shift to the west, and may be related to a reduction of plate convergence rate and shallowing plate dip.  The coastline has migrated little from late Miocene to present.  The Cascadia forearc basin may be equivalent to the Neogene Eel River basin off northern California, and analagous to the ancient Cretaceous Great Valley and the modern Java-Sumatra system, with a deep forearc basin bound to the west by an active accretionary wedge.  Filling of the Cascadia basin in the Pleistocene and erosion of the continental shelf during late Pleistocene lowstands resulted in the forearc geometry seen today.  Comparison of offshore and onshore margin-parallel uplift rates reveal many similarities, including low uplift on the central Oregon margin which may represent low plate coupling.

 

Objectives

  • To identify the late Miocene-early Pliocene age unconformity on the Oregon shelf and produce a structure contour map of this surface.
  • To use the structure contour map to determine the geometry of the former Neogene forearc basin.
  • To use the unconformable surface to identify active structures.
  • To compare onshore uplift rates (e.g., highway releveling surveys, Pleistocene terrace datums) with offshore net vertical motions to determine margin parallel variations in deformation.
Cascadia subduction zone listric normal faulting map

Figure 1.  Tectonic map of the Cascadia subduction zone.  Yellow box indicates study area and location of other figures.
 

Methods

A grid of multichannel migrated seismic reflection profiles was used to map out the current depth of the unconformable surface (Figure 2). The late Miocene-early Pliocene unconformity was initially identified from interpretations of benthic foramenifera (S. Drewry et al., unpublished data) taken from industry boreholes.  Where the unconformity is angular on the inner to middle shelf, the surface could be easilyCascadia subduction zone unconformity faulting reflection profile map of unconformities Figure 2. Map of the central and northern Oregon continental shelf and slope.  Positions of seismic reflection datasets, seafloor samples, and exploratory wells used to produce the structure contour map of the late Miocene unconformity are shown.

traced along the network of profiles.  Farther seaward, the non-angular reflectors may represent a disconformity or a correlative conformity.  All available dated seafloor samples (Figure 2) were used to identify Miocene outcrops on the seafloor.  The unconformity was found to be continuously traceable on much of the northern and central Oregon margin, with correlation to the north into Washington and south into southern Oregon more complex.
        The unconformity was digitized to produce an xyz file of unconformity position, with z initially in seconds two-way time, and later
converted to depth using appropriate velocities from seismic refraction surveys and sonic logs.  Depths shown here are below current sea level.  The identification of a younger late Pliocene-Pleistocene surface (angularly unconformable in places) was used to sub-divide the post-Miocene section into Pliocene and Quaternary units.  These were assigned velocities of 2.1 and 1.7 km/s respectively.  The resulting xyz data were used to construct structure contours of the unconformity.

Cascadia subduction zone unconformity faulting reflection profile map of unconformities reflection profile

Figure 3. (click for larger image) Multichannel migrated seismic reflection profile on the central Oregon inner shelf, west of Cape Foulweather.  This seismic profile clearly shows the angular late Miocene-early Pliocene age unconformity (PM) dipping to the west from the coastline.  The unconformity truncates the middle Miocene Columbia River Basalt Group (CRBG) flows.  Thick sequences of basin strata of Eocene to late Miocene age lie below the unconformity and increase in thickness above the unconformity to the west.  The unconformity is angular throughout much of the inner and middle shelf and is presumed to have been eroded subaerially.

Figure 2. Trackline map for MCS profiles used in the study.

Cascadia subduction zone unconformity faulting reflection profile map of unconformities reflection profile

Figure 4.Multichannel migrated seismic reflection profile across the central Oregon shelf, west of Yaquina and Alsea Bays.  This profile crosses Stonewall Bank anticline and Newport syncline to the east, a remanent of the broad early to mid Tertiary forearc basin.  The angular late Miocene-early Pliocene unconformity (PM) truncates late and middle Miocene strata east of Stonewall Bank, including the Columbia River Basalt Group (CRBG).  West of Stonewall Bank, strata are parallel with little sign of angular unconformity.  The late Miocene-early Pliocene boundary is thought to be a disconformity or correlative conformity in this region.  Miocene strata are uplifted and exposed on Stonewall Bank.  The absence of significant thinning of Pliocene-Pleistocene strata across Stonewall Bank indicates that the anticline began to grow as recently as the late Pliocene or Pleistocene.  Yeats et al. (1997) suggest that the bank is uplifted by a blind reverse fault capable of generating an Mw=6.8 earthquake.

 

Cascadia subduction zone unconformity faulting reflection profile map of unconformities

Figure 5. (left) Shaded relief image of the late Miocene-early Pliocene unconformity structure contour map on the central and northern Oregon continental shelf.  The western edge of the image represents the current extent of basinal sediments, although the basin may have extended farther west and since been eroded.  The unconformity reaches the seafloor at the eastern edge of the shaded image, where middle Miocene and older formations are exposed.  The unconformity is deformed by Pliocene and Quaternary structures including the Stonewall Bank anticline, Newport syncline, uplifted submarine banks (Heceta, Nehalem, Siltcoos), the Nehalem Bank fault, and the left-lateral Daisy Bank fault.  Cross sections of the unconformable surface, A-A', B-B', and C-C' are shown in Figure 6.  D-D' represents the representative margin-parallel section used to compare relative offshore vertical motions with onshore uplfit rates (Figure 8). Uplift rate contours (mm/yr) determined from highway releveling surveys during the last 50 years are shown onshore in light blue.  Notice the coincidence of negligible onshore uplift rates between 44.5° and 45.5° N with the deep basin deforming the unconformity (including the Newport syncline). Depths are below sea level.

Cascadia subduction zone unconformity faulting reflection profile map of unconformities

Figure 6. (right) Cross sections of the late Miocene-early Pliocene unconformity taken across the shaded relief image of Figure 5.  The E-W profile, A-A', crosses the Stonewall Bank anticline and Newport syncline to the east.  The unconformity is at a maximum depth of 2500 m in the axis of the syncline, but uplifted and eroded at Stonewall Bank.  B-B' crosses Heceta Bank, one of several prominent and recently uplifted submarine banks on the Oregon margin.  C-C' crosses the northward extension of the Newport syncline and the Nehalem Bank fault.  This fault uplifts and truncates the unconformity and projects into Netarts Bay where it deforms late Pleistocene sediments.

 

Cascadia subduction zone unconformity faulting reflection profile map of unconformities

 

 

 

Figure 7.  Perspective view to the south of shaded relief image of the late Miocene-early Pliocene unconformity structure contour map, between 45.5° and 43.5° N.  The present coastline would be located on the left of this image.  This image clearly shows the young uplifted submarine banks of the Oregon margin, Stonewall, Siltcoos and Heceta, where Miocene strata are uplifted to the seafloor and eroded.  The WNW-trending left lateral Daisy Bank fault also deforms the unconformable surface.  This fault offsets Quaternary folds of the modern accretionary prism and abyssal plain sediments to the west.  The unconformity reaches the seafloor at the eastern edge of the shaded image, and middle Miocene and older formations are exposed on the innermost shelf and onshore.

 

Assumptions

        The precise age of the unconformity is unknown, although benthic forams and seafloor samples suggest a late Miocene or early Pliocene age. We hypothesize that the unconformity represents a worldwide hiatus (NH6) in the late Miocene (6-7.5 Ma), recorded at ODP sites including those of the northeast Pacific (Keller and Barron, 1987).  The unconformity (and correlative conformity) may be time transgressive.  In some regions, the unconformity was difficult to trace (due to non-angularity or faulting), prodcuing some error in correlation.  We assume that the angular unconformity was sub-aerial on the inner and middle shelf, and therefore initially at approximately the same depth parallel to the coastline.  The current depth of this surface can therefore be used to determine relative uplift rates on the shelf.

 

Basin Geometry

        The structure contour map of the late Miocene-early Pliocene unconformity delineates a deformed broad elongate forearc basin underlying the current Oregon shelf and upper slope.  Forearc basinal strata above the Pliocene-late Miocene unconformity attain thicknesses of up to 2500m off central Oregon, with even greater thicknesses of underlying Eocene to late Miocene sediments.  The current seaward limit of basinal strata is marked by a N-S-trending outer-arc high.  Strata underlying the late Miocene unconformity, and early Pliocene strata in some cases, do not thin or onlap against this structural high.  We therefore hypothesize that the forearc basin extended farther seaward prior to growth of this high.  The basin continued to fill into the early Pleistocene, whereas sediments currently bypass the shelf and are accumulating in slope basins and on the abyssal plain.  Basin strata have been uplifted by late Pliocene and Quaternary structures and subsequently eroded.  Paleo-water depths indicate shallowing up section, suggesting that sedimentation rates exceeded tectonic subsidence.
        Prior to Coast Range uplift, the forearc basin extended from the current continental slope to the Willamette Valley east of the Coast Range. The Coast Range marked the landward boundary of this forearc basin following uplift in the late Miocene.  Pliocene-Pleistocene strata onlap against the late Miocene unconformity and dip westward indicating continued uplift of the Coast Range and growth of the basin from late Miocene to present.  The position of the unconformity at the seafloor on the inner most shelf, close to the present coastline, suggests that the coastline has not migrated significantly from late Miocene to present.  This suggests that during Coast Range uplift and subsidence of the westward forearc basin, the coastline has acted as a hingeline.  With the onset of Coast Range uplift, the axis of the active forearc basin shifted to the west. Uplift may have been associated with a shallowing subducting plate due to changes in plate convergence rate.

 

Margin Parallel Uplift Rates

        Assuming the undeformed late Miocene unconformity was subaerially eroded on the inner shelf, deformation of this surface can be used to determine relative net uplift and subsidence rates along the margin. Comparisons were made with onshore uplift rates from highway releveling surveys (Mitchell et al., 1994) and uplifted Pleistocene marine terraces (West, 1986).  Low uplift rates from releveling and marine terraces between 44.5° and 45° N are coincident with the deepest region of the offshore unconformity, the Newport syncline.  To the south of Yaquina Bay, between 44.5° and 43°N, generally higher onshore uplift rates coincide with the unconformity at shallower depths.  Between 44° and 45°N, the depth of the late Miocene unconformity shows many similarities to the pattern of uplift of the 80ka marine terrace.  North of 45°N, the depth to the offshore unconformity shallows, coincident with increasing uplift rates from highway releveling.  Relative trends of uplift and subsidence along the margin have remained similar from the latest Miocene to present.  Low uplift rates in central Oregon may be a result of low coupling on the subduction zone in this region, and may represent a segment boundary, as suggested by Kelsey et al. (1994).
 
Cascadia subduction zone unconformity faulting reflection profile map of unconformities

Figure 8. Comparison of relative uplift rates onshore and offshore. Onshore datasets are (a) uplift rates from highway releveling surveys for the last 50 years and (b) uplifted late Pleistocene marine terraces (80-220 ka).  The offshore dataset represents a cross section (D-D' of Figure 5) approximately parallel to the margin and coastline of the late Miocene-early Pliocene unconformity.  Note the low uplift rates or subsidence between 44.5° and 45° N.
 
 

Deformation of the Late Miocene-Pliocene Unconformity

        The unconformity is deformed by post-late Miocene structures on the continental shelf and upper slope.  The current shelf break post-dates the basin geometry and deformation, with synclinal basin axes and the outer-arc high (marking the seaward extent of forearc basin deposits) crossing this topographic boundary.  The shelf break is in part controlled by the positions of major uplifted submarine banks, namely Heceta and Nehalem Bank, and intervening embayments.  Structures underlying these banks are young - the absence of significant growth strata within much of the post-late Miocene unconformity sequence suggests a late Pliocene to Pleistocene age.  Stonewall Bank anticline deforms the formerly broad basin and uplifts late Miocene strata to the seafloor, with evidence of 1500-4000 m of eroded strata from the crest of the anticline (Yeats et al., 1997). Absence of onlapping Pliocene strata against the late Miocene unconformity and thickening rather than thinning of much of the earlier Pliocene-Pleistocene sequence indicate that this anticline bagan to form during the late Pliocene.  Yeats et al. (1997) hypothesize that this structure is underlain by a blind reverse fault.  Uplift of Stonewall Bank anticline isolates a remanent of the former forearc basin, the Newport syncline.  The Nehalem Bank fault, due west of Netarts and Tillamook Bays, uplifts the unconformity and Miocene strata to the seafloor.  This fault also deforms and offsets Quaternary strata and projects onshore as the Happy Camp Fault at Netarts Bay, which may be structurally controlled.  One of several WNW-trending left-lateral faults, which cross the Cascadia margin from the abyssal plain to the shelf edge, the Daisy Bank fault (Goldfinger et al., 1997), deforms the late Miocene unconformity west of Stonewall Bank.
 

Summary

        The structure contour map of the late Miocene-early Pliocene unconformity outlines a former broad elongate forearc basin, possibly
analagous to the Eel River Basin off northern California, which has subsequently been deformed by structures active during the Pliocene and Quaternary.  Prior to Coast Range uplift and erosion of the western edge of the basin, this forearc basin extended from the present continental slope to the Willamette Valley.  Modern and ancient analogues of deep elongate forearc basins include the Java-Sumatra system and the Cretaceous Great Valley.  Comparisons of the deformed unconformity with onshore datasets indicate similar variations in margin-parallel uplift rates.  Coastal and offshore central Oregon is characterized by very low uplift rates or subsidence, whereas uplift rates are higher to the north and south.  Low uplift may be a result of low coupling on the subduction zone, and this region may act as a segment boundary during subduction zone earthquakes.

 

Publications

 

McNeill, L.C., Goldfinger, C., Kulm, L.D., and Yeats, R.S., 2000, Tectonics of the Neogene Cascadia forearc basin: Investigations of a deformed late Miocene unconformity: Geological Society of America Bulletin, v. 112, p. 1209-1224.

 

References

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.

Keller, G., and Barron, J.A., 1987, Paleodepth distribution of Neogene
deep-sea hiatuses:  Paleoceanography, v. 2, p. 697-713.

Kelsey, H.M., Engebretson, D.C., Mitchell, C.E., and Ticknor, R.L., 1994,
Topographic form of the Coast Ranges of the Cascadia margin in relation to
coastal uplift rates and plate subduction:  Journal of Geophysical
Research, v. 99, p. 12,245-12,255.

Mitchell, C.E., Vincent, P., Weldon II, R.J., and Richards, M.A., 1994,
Present-day vertical deformation of the Cascadia margin, Pacific northwest,
U.S.A.:  Journal of Geophysical Research, v. 99, p. 12,257-12,277.

West, D.O., 1986, WNP-3 Geologic support services, Coastal terrace study:
Report prepared for Washington Public Power Supply System.

Yeats, R.S., Kulm, L.D., Goldfinger, C., and McNeill, L.C., in press,
Antecedent stream at Stonewall Bank:  Slip rate on a blind fault beneath
the Oregon continental shelf:  Geological Society of America Bulletin.