Slope failures within and upstream of Lake Quinault, Washington, as uneven responses to Holocene earthquakes along the Cascadia subduction zone

2017 ◽  
Vol 89 (1) ◽  
pp. 178-200 ◽  
Author(s):  
Elana L. Leithold ◽  
Karl W. Wegmann ◽  
Delwayne R. Bohnenstiehl ◽  
Stephen G. Smith ◽  
Anders Noren ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Coastal Marsh ◽  
Seismic Survey ◽  
Cascadia Subduction Zone ◽  
Survey Analysis ◽  
Delta Front ◽  
Data Set ◽  
Reflection Seismic ◽  
Partial Channel ◽  
Western Washington

AbstractInvestigation of Lake Quinault in western Washington, including a reflection seismic survey, analysis of piston cores, and preliminary mapping in the steep, landslide-prone Quinault River catchment upstream of the lake, reveals evidence for three episodes of earthquake disturbance in the past 3000 yr. These earthquakes triggered failures on the lake’s underwater slopes and delta front, as well as subaerial landsliding, partial channel blockage, and forced fluvial sediment aggradation. The ages of the three Lake Quinault disturbance events overlap with those of coseismically subsided, coastal marsh soils nearby in southwest Washington that are interpreted to record ruptures of the Cascadia megathrust. Absent from Lake Quinault, however, are signals of obvious disturbance from five additional subduction earthquakes inferred to have occurred during the period of record. The lack of evidence for these events may reflect the limitations of the data set derived from the detrital, river-dominated lake stratigraphy but may also have bearing on debates about segmentation and the distribution of slip along the Cascadia subduction zone during prior earthquakes.

Upper mantle structure of the northern Cascadia subduction zone

1995 ◽  
Vol 32 (1) ◽  
pp. 1-12 ◽  
Author(s):  
M. G. Bostock ◽  
J. C. Vandecar
Keyword(s):  
British Columbia ◽  
Subduction Zone ◽  
Upper Mantle ◽  
Puget Sound ◽  
Cascadia Subduction Zone ◽  
Mantle Structure ◽  
Data Set ◽  
Juan De Fuca Plate ◽  
Upper Mantle Structure ◽  
Juan De Fuca

Previous knowledge of the structure of the Cascadia subduction zone north of the Canada–United States border has been derived from a variety of geophysical studies that accurately delineated the downgoing Juan de Fuca plate from the offshore deformation front to depths of ~50–60 km beneath south-central Vancouver Island and the Georgia Strait. Little is known, however, of the structure of the Cascadia subduction zone farther westward and to greater depths in the upper mantle. We have assembled a set of some 1100 teleseismic traveltimes from events recorded on the Western Canadian Telemetered Network to augment a previously existing data set recorded on the Washington Regional Seismograph Network. The composite data set is inverted for upper mantle structure below Washington, Oregon, and southwestern British Columbia. We analyze the new northern portion of the model between 48.5–50°N and 118–127°W, which provides the first images of the deep slab structure in this region. The model is parameterized using splines under tension over a dense grid of knots. The nonlinearity of the inverse problem is treated by iteratively performing three-dimensional ray tracing and linear inversion. Resolution tests performed with a synthetic slab model indicate that the deep structure is resolved by the data north to at least 50°N. The inversions are characterized by a quasi-planar, high-velocity body inferred to represent the thermal and compositional anomaly of the subducted Juan de Fuca plate. This body exhibits velocity deviations of up to 3% from the background reference model and extends to depths of at least 400–500 km. The depth contours of the slab in the upper mantle mimic those of the shallow slab by changing strike, in the latitude range 48.0–48.5°N, from north–south in Washington to northwest–southeast in southern British Columbia. This forces the development of two arch-type structures: a main arch observed in previous studies trending east–west over Puget Sound and a possible second arch extending northeasterly from the Georgia Strait into the British Columbia interior. A steepening of the deep slab dip from British Columbia south towards Puget Sound and complexity in the evolution of the arches in depth may be the result of a change in plate motions at 3.5 Ma associated with the detachment of the Explorer plate.

Repeated megaturbidite deposition in Lake Crescent, Washington, USA, triggered by Holocene ruptures of the Lake Creek-Boundary Creek fault system

2019 ◽  
Vol 131 (11-12) ◽  
pp. 2039-2055 ◽  
Author(s):  
Elana L. Leithold ◽  
Karl W. Wegmann ◽  
Delwayne R. Bohnenstiehl ◽  
Catelyn N. Joyner ◽  
Audrianna F. Pollen
Keyword(s):  
Critical Infrastructure ◽  
Fault Scarp ◽  
Seismic Survey ◽  
Fault System ◽  
Olympic Peninsula ◽  
Reflection Seismic ◽  
The North ◽  
Dextral Shear ◽  
Western Washington ◽  
Late Pleistocene To Holocene

Abstract Lake Crescent, a 180-m-deep, glacially carved lake located on the Olympic Peninsula in western Washington, USA, overlies the Lake Creek-Boundary Creek fault zone, a system of structures with at least 56 km of late Pleistocene to Holocene surface rupture. Investigation of the lake’s sediment, including a reflection seismic survey and analysis of piston cores, reveals evidence that the fault beneath the lake has ruptured four times in the past ∼7200 years, producing unusually thick deposits termed megaturbidites. The earthquakes triggered rockslides that entered the lake and caused displacement waves (lake tsunamis) and seiches, most recently ca. 3.1 ka. Seismic reflection results from beneath the depth of core penetration reveal at least two older post-glacial ruptures that are likely to have similarly affected the lake. The stratigraphy of Lake Crescent provides insight into the behavior of a fault system that partially accommodates regional clockwise rotation and contraction of the northern Cascadia forearc through oblique dextral shear, and highlights the potential for disruption to critical infrastructure, transportation corridors, and industry on the North Olympic Peninsula during future surface-rupturing earthquakes. Our results illustrate the potential synergism between lacustrine paleoseismology and fault-scarp trench investigations. More precise dating of strong earthquake shaking afforded by continuous accumulation of lake sediment improves earthquake histories based on trenched fault scarp exposures, which are commonly poorly dated.

THE TIMING AND DEFORMATION OF CASCADIA SUBDUCTION ZONE EARTHQUAKES FROM COASTAL MARSH RECORDS OF OREGON

2017 ◽  
Author(s):  
Simon E. Engelhart ◽  
◽  
Niamh Cahill ◽  
Andrea Hawkes ◽  
Benjamin P. Horton ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Coastal Marsh ◽  
Cascadia Subduction Zone ◽  
Subduction Zone Earthquakes

Performance of Lightly Confined Reinforced Concrete Columns in Long-Duration Subduction Zone Earthquakes

2005 ◽  
Vol 1928 (1) ◽  
pp. 184-192
Author(s):  
Seth E. Stapleton ◽  
Cole C. McDaniel ◽  
William F. Cofer ◽  
David I. McLean
Keyword(s):  
Reinforced Concrete ◽  
Subduction Zone ◽  
Concrete Columns ◽  
Cascadia Subduction Zone ◽  
Longitudinal Reinforcement ◽  
Reinforced Concrete Columns ◽  
Lap Splice ◽  
Western Washington ◽  
Subduction Zone Earthquake ◽  
Subduction Zone Earthquakes

The main goals of this research were to evaluate typical 1950s and 1960s as-built bridge columns in western Washington State in large subduction zone earthquakes and to investigate the dependency of failure mechanisms on loading history. Eight displacement histories were applied to eight nominally identical, half-scale, circular reinforced concrete columns expected to respond primarily in flexure (flexure-dominated). The main design deficiencies were a short longitudinal reinforcement lap splice at the base of the column (35 db) and inadequate transverse reinforcement. Test results showed that the failure mode of reinforced concrete columns was controlled by the column loading history. Three distinct failure mechanisms were observed for columns with an aspect ratio of approximately 4.2, assuming symmetric, double-curvature behavior. Large initial displacements greater than six times the effective yield displacement (Δ y) were likely to result in shear failures. Columns experiencing many displacements less than 4Δ y were likely to fail because of longitudinal reinforcement buckling. Columns subjected to several displacement excursions less than 4Δ y followed by an excursion greater than 6Δ y were likely to fail by longitudinal reinforcement slipping within the splice region. Despite the deficiencies present in circular reinforced concrete bridge columns built before 1975 in western Washington State, this study showed that flexure-dominated columns with a 35 db lap splice in multiple-column bent, three-or four-span bridges were not likely to experience significant damage in the predicted Cascadia Subduction Zone earthquake. However, other components of the bridge need to be assessed to determine whether the global bridge response is acceptable under the predicted Cascadia Subduction Zone earthquake.

Source Investigation and Comparison of the 1939, 1946, 1949 and 1965 Earthquakes, Cascadia Subduction Zone, Western Washington

2007 ◽  
Vol 164 (10) ◽  
pp. 1905-1919 ◽  
Author(s):  
Katy R. Wiest ◽  
Diane I. Doser ◽  
Aaron A. Velasco ◽  
James Zollweg
Keyword(s):  
Subduction Zone ◽  
Cascadia Subduction Zone ◽  
Western Washington

ASSESSING THE UTILITY OF δ13C AND BULK GEOCHEMISTRY IN ESTUARIES ALONG THE CASCADIA SUBDUCTION ZONE FOR COASTAL PALEOSEISMOLOGY

2017 ◽  
Author(s):  
Robert J. O'Donnell ◽  
◽  
Andrea D. Hawkes ◽  
Chad S. Lane ◽  
Simon E. Engelhart ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Cascadia Subduction Zone
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