Mapping the megathrust beneath the northern Gulf of Alaska using wide‐angle seismic data

Brocher, Thomas M.; Fuis, Gary S.; Fisher, Michael A.; Plafker, George; Moses, Michael J.; Taber, John; Christensen, Nikolas I.

doi:10.1029/94jb00111

Cited by 141 publications

(195 citation statements)

References 39 publications

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“…The Yakutat microplate is relatively buoyant, which results in a subduction angle of approximately 3°beneath PWS compared to the steeper 8°dip along the Kodiak segment [e.g., Brocher et al, 1994;Eberhart-Phillips et al, 2006;Doser and Veilleux, 2009]. The maximum slip from the 1964 earthquake was largely coincident with the southwestern edge of the subducted Yakutat terrane, which appears to be largely coupled to the underlying Pacific plate [Zweck et al, 2002;Doser et al, 2004;Eberhart-Phillips et al, 2006;Ichinose et al, 2007].…”

Section: Introductionmentioning

confidence: 95%

“…Brocher et al [1994] published crustal refraction and wide-angle reflection results along transects that cross the PWS area. The PWS profile extends the length of Montague Strait southwest into the Gulf of Alaska, obliquely crossing the Hanning Bay fault, Patton Bay fault, Cape Cleare fault, and Junken Trough (Figure 1).…”

Section: Deep Splay Fault Geometry From Seismic Imagesmentioning

confidence: 99%

“…The hypocenter was at the top of the Wadati-Benioff zone of seismicity. This depth also correlates with a boundary showing a large seismic velocity contrast [e.g., Brocher et al, 1994;Oleskovich, et al, 1999;Doser and Veilleux, 2009;Fuis et al, 2008]. The earthquake initiated at the zone between the downgoing Yakutat and Pacific plates, but rupture propagated along splay faults through the subducted Yakutat terrane and overlying accretionary complex [Plafker, 1969;Brocher et al, 1994;Eberhart-Phillips et al, 2006;Fuis et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

“…The megathrust beneath PWS is the contact between the subducting Yakutat terrane and the overlying accretionary complex, referred to as the Prince William terrane [Brocher et al, 1994]. West of Montague Island, the subducting Yakutat slab is absent and the Pacific Plate subducts directly beneath the North American plate [e.g., Brocher et al, 1994;EberhartPhillips et al, 2006].…”

Section: Introductionmentioning

confidence: 99%

“…West of Montague Island, the subducting Yakutat slab is absent and the Pacific Plate subducts directly beneath the North American plate [e.g., Brocher et al, 1994;EberhartPhillips et al, 2006]. The PWS asperity, defined as a region of high moment release [e.g., Lay et al, 1982;Scholz and Campos, 2012], was centered beneath the southwest end of Montague Island near a prominent magnetic high that defines the western boundary of the subducted Yakutat terrane (Figure 1) [Bruns, 1983;Griscom and Sauer, 1990;Brocher et al;1994;Johnson et al, 1996;Zweck et al, 2002;Eberhart-Phillips et al, 2006].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2013

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[1] High-resolution sparker and crustal-scale air gun seismic reflection data, coupled with repeat bathymetric surveys, document a region of repeated coseismic uplift on the portion of the Alaska subduction zone that ruptured in 1964. This area defines the western limit of Prince William Sound. Differencing of vintage and modern bathymetric surveys shows that the region of greatest uplift related to the 1964 Great Alaska earthquake was focused along a series of subparallel faults beneath Prince William Sound and the adjacent Gulf of Alaska shelf. Bathymetric differencing indicates that 12 m of coseismic uplift occurred along two faults that reached the seafloor as submarine terraces on the Cape Cleare bank southwest of Montague Island. Sparker seismic reflection data provide cumulative Holocene slip estimates as high as 9 mm/yr along a series of splay thrust faults within both the inner wedge and transition zone of the accretionary prism. Crustal seismic data show that these megathrust splay faults root separately into the subduction zone décollement. Splay fault divergence from this megathrust correlates with changes in midcrustal seismic velocity and magnetic susceptibility values, best explained by duplexing of the subducted Yakutat terrane rocks above Pacific plate rocks along the trailing edge of the Yakutat terrane. Although each splay fault is capable of independent motion, we conclude that the identified splay faults rupture in a similar pattern during successive megathrust earthquakes and that the region of greatest seismic coupling has remained consistent throughout the Holocene.

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Section: Introductionmentioning

confidence: 95%

Section: Deep Splay Fault Geometry From Seismic Imagesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2013

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Triggered tremor sweet spots in Alaska

Gomberg

Prejean

2013

JGR Solid Earth

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To better understand what controls fault slip along plate boundaries, we have exploited the abundance of seismic and geodetic data available from the richly varied tectonic environments composing Alaska. A search for tremor triggered by 11 large earthquakes throughout all of seismically monitored Alaska reveals two tremor “sweet spots”—regions where large‐amplitude seismic waves repeatedly triggered tremor between 2006 and 2012. The two sweet spots locate in very different tectonic environments—one just trenchward and between the Aleutian islands of Unalaska and Akutan and the other in central mainland Alaska. The Unalaska/Akutan spot corroborates previous evidence that the region is ripe for tremor, perhaps because it is located where plate‐interface frictional properties transition between stick‐slip and stably sliding in both the dip direction and laterally. The mainland sweet spot coincides with a region of complex and uncertain plate interactions, and where no slow slip events or major crustal faults have been noted previously. Analyses showed that larger triggering wave amplitudes, and perhaps lower frequencies (<~0.03 Hz), may enhance the probability of triggering tremor. However, neither the maximum amplitude in the time domain or in a particular frequency band, nor the geometric relationship of the wavefield to the tremor source faults alone ensures a high probability of triggering. Triggered tremor at the two sweet spots also does not occur during slow slip events visually detectable in GPS data, although slow slip below the detection threshold may have facilitated tremor triggering.

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Alaska Megathrust 2: Imaging the megathrust zone and Yakutat/Pacific plate interface in the Alaska subduction zone

et al. 2014

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We image the slab underneath a 450 km long transect of the Alaska subduction zone to investigate (1) the geometry and velocity structure of the downgoing plate and their relationship to slab seismicity and (2) the interplate coupled zone where the great 1964 earthquake (M w 9.2) exhibited the largest amount of rupture. The joint teleseismic migration of two array data sets based on receiver functions (RFs) reveals a prominent, shallow-dipping low-velocity layer at~25-30 km depth in southern Alaska. Modeling of RF amplitudes suggests the existence of a thin layer (V s of~2.1-2.6 km/s) that is~20-40% slower than underlying oceanic crustal velocities, and is sandwiched between the subducted slab and the overriding plate. The observed megathrust layer (with V p /V s of 1.9-2.3) may be due to a thick sediment input from the trench in combination with elevated pore fluid pressure in the channel. Our image also includes an unusually thick low-velocity crust subducting with a~20°dip down to 130 km depth at~200 km inland beneath central Alaska. The unusual nature of this subducted segment results from the subduction of the Yakutat terrane crust. Our imaged western edge of the Yakutat terrane aligns with the western end of a geodetically locked patch with high slip deficit, and coincides with the boundary of aftershock events from the 1964 earthquake. It appears that this sharp change in the nature of the downgoing plate could control the slip distribution of great earthquakes on this plate interface.

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Mapping the megathrust beneath the northern Gulf of Alaska using wide‐angle seismic data

Cited by 141 publications

References 39 publications

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

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

Triggered tremor sweet spots in Alaska

Alaska Megathrust 2: Imaging the megathrust zone and Yakutat/Pacific plate interface in the Alaska subduction zone

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