Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

Liberty, Lee M.; Finn, S.; Haeussler, Peter J.; Pratt, Thomas L.; Peterson, Andrew

doi:10.1002/jgrb.50372

Cited by 22 publications

(73 citation statements)

References 48 publications

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“…The epicenter was located in northern PWS and west of the town of Valdez, and approximately 150 km north of the location of greatest coseismic surface uplift ( Fig. 1; Plafker, 1969;Liberty et al, 2013). Damage from ground shaking was widespread, and the associated tsunamis inundated coastline infrastructure as far away as northern California.…”

Section: The 1964 Great Alaska Earthquakementioning

confidence: 99%

“…Damage from ground shaking was widespread, and the associated tsunamis inundated coastline infrastructure as far away as northern California. Local tsunamis damaged the Alaska (Wilson and Hults, 2012;Liberty et al, 2013;Haeussler et al, 2015). Faults that slipped during the 1964 Great Alaska earthquake include the Patton Bay fault (PBF), Hanning Bay fault (HBF), and Cape Cleare fault (CCF).…”

Section: The 1964 Great Alaska Earthquakementioning

confidence: 99%

“…Although large earthquakes along the Alaska-Aleutian megathrust typically result from the northward subduction of the Pacific plate beneath the North American plate, the PWS area includes the added subduction of the Yakutat terrane that appears to locally override the Pacific plate (e.g., Brocher et al, 1994;Eberhart-Phillips et al, 2006). During the 1964 earthquake, and likely during most Holocene megathrust earthquakes in the area, the largest coseismic surface ruptures were associated with splay faults that surface near the southwest limits of PWS (Plafker, 1969;Liberty et al, 2013). To date, there has been little direct evidence that these active splay faults extend northeast beneath PWS, closer to the 1964 earthquake epicenter and the population centers of Valdez and Cordova.…”

Section: Introductionmentioning

confidence: 99%

“…Splay faults that extend from the subduction interface to the seafloor or land on the Alaska continental shelf accommodate the bulk of upper-plate coseismic motion for large earthquakes in the region, and these thrust faults strongly influence island formation in the PWS area (e.g., Plafker, 1969;Liberty et al, 2013;Haeussler et al, 2015). The only documented surface ruptures from the 1964 earthquake occurred on Montague Island in southwest PWS and on the adjacent Gulf of Alaska seafloor ( Fig.…”

Section: Introductionmentioning

confidence: 99%

“…1; Plafker, 1969). These surface-rupturing faults accommodated much of the 21 m of slip caused by the earthquake, with upward of 5-12 m vertical uplift on multiple faults (Plafker, 1969;Liberty et al, 2013). Although Plafker (1969) documented no vertical displacement on individual faults on the islands of eastern PWS, upwards of 2 m of regional tectonic uplift may indicate coseismic slip on submarine faults in this area.…”

Section: Introductionmentioning

confidence: 99%

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Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

Finn¹,

Liberty²,

Haeussler³

et al. 2015

Bulletin of the Seismological Society of America

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We present new marine seismic-reflection profiles and bathymetric maps to characterize Holocene depositional patterns, submarine landslides, and active faults beneath eastern and central Prince William Sound (PWS), Alaska, which is the eastern rupture patch of the 1964 M w 9.2 earthquake. We show evidence that submarine landslides, many of which are likely earthquake triggered, repeatedly released along the southern margin of Orca Bay in eastern PWS. We document motion on reverse faults during the 1964 Great Alaska earthquake and estimate late Holocene slip rates for these growth faults, which splay from the subduction zone megathrust. Regional bathymetric lineations help define the faults that extend 40-70 km in length, some of which show slip rates as great as 3:75 mm=yr. We infer that faults mapped below eastern PWS connect to faults mapped beneath central PWS and possibly onto the Alaska mainland via an en echelon style of faulting. Moderate (M w > 4) upper-plate earthquakes since 1964 give rise to the possibility that these faults may rupture independently to potentially generate M w 7-8 earthquakes, and that these earthquakes could damage local infrastructure from ground shaking. Submarine landslides, regardless of the source of initiation, could generate local tsunamis to produce large run-ups along nearby shorelines. In a more general sense, the PWS area shows that faults that splay from the underlying plate boundary present proximal, perhaps independent seismic sources within the accretionary prism, creating a broad zone of potential surface rupture that can extend inland 150 km or more from subduction zone trenches.

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Section: The 1964 Great Alaska Earthquakementioning

confidence: 99%

Section: The 1964 Great Alaska Earthquakementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

Finn¹,

Liberty²,

Haeussler³

et al. 2015

Bulletin of the Seismological Society of America

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Continuous uplift near the seaward edge of the Prince William Sound megathrust: Middleton Island, Alaska

et al. 2014

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Middleton Island, located at the seaward edge of the continental shelf 50 km from the base of the inner wall of the Aleutian Trench, affords an opportunity to make land-based measurements of uplift near the toe of the Prince William Sound megathrust, site of the 1964, M = 9.2, Alaska earthquake. Leveling surveys on Middleton Island indicate roughly uniform tilting (~1 μrad/a down to the northwest) of the island, and GPS surveys (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) show an uplift rate of 14 mm/a of the island relative to fixed North America. The data are consistent with a combined (coseismic and postseismic) uplift (in meters) due to the 1964 earthquake as a function of time τ (years after the earthquake) u(τ) = (3.5 + 1.21 log 10 [1 + 1.67 τ]) H(τ) where 3.5 is the coseismic uplift and H(τ) is 0 for τ < 0 and 1 otherwise. The current uplift on Middleton Island is attributed to continuous slip on a fault splaying off from the megathrust, and the long-term uplift is the superposition of the effects of past earthquakes, each earthquake being similar to the 1964 event. Then, the predicted uplift at time t due to a sequence of earthquakes at times t i would beFrom studies of strandlines associated with the uplifted terraces on Middleton Island, Plafker et al. (1992) estimated the occurrence times of the last six earthquakes and measured the present-day elevations of those strandlines. The predicted uplift is in rough agreement with those measurements. About half of the predicted uplift is due to postseismic relaxation from previous earthquakes.

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Quantifying offshore fore‐arc deformation and splay‐fault slip using drowned Pleistocene shorelines, Arauco Bay, Chile

et al. 2017

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Most of the deformation associated with the seismic cycle in subduction zones occurs offshore and has been therefore difficult to quantify with direct observations at millennial timescales. Here we study millennial deformation associated with an active splay‐fault system in the Arauco Bay area off south central Chile. We describe hitherto unrecognized drowned shorelines using high‐resolution multibeam bathymetry, geomorphic, sedimentologic, and paleontologic observations and quantify uplift rates using a Landscape Evolution Model. Along a margin‐normal profile, uplift rates are 1.3 m/ka near the edge of the continental shelf, 1.5 m/ka at the emerged Santa María Island, −0.1 m/ka at the center of the Arauco Bay, and 0.3 m/ka in the mainland. The bathymetry images a complex pattern of folds and faults representing the surface expression of the crustal‐scale Santa María splay‐fault system. We modeled surface deformation using two different structural scenarios: deep‐reaching normal faults and deep‐reaching reverse faults with shallow extensional structures. Our preferred model comprises a blind reverse fault extending from 3 km depth down to the plate interface at 16 km that slips at a rate between 3.0 and 3.7 m/ka. If all the splay‐fault slip occurs during every great megathrust earthquake, with a recurrence of ~150–200 years, the fault would slip ~0.5 m per event, equivalent to a magnitude ~6.4 earthquake. However, if the splay‐fault slips only with a megathrust earthquake every ~1000 years, the fault would slip ~3.7 m per event, equivalent to a magnitude ~7.5 earthquake.

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Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

Cited by 22 publications

References 48 publications

Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

Continuous uplift near the seaward edge of the Prince William Sound megathrust: Middleton Island, Alaska

Quantifying offshore fore‐arc deformation and splay‐fault slip using drowned Pleistocene shorelines, Arauco Bay, Chile

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