Crustal Uplift Southwest of Montague Island, Alaska

Malloy, Richard J.

doi:10.1126/science.146.3647.1048

Cited by 18 publications

(17 citation statements)

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“…Anomalously high uplift rates are suggested for southern Nagai Island, where one data point suggests uplift of 6 m/ka, and for Big Koniuji Island where two points suggest uplift of 12 m/ka (Figures 2,3c, and 4b). Although these faster rates are based on few data points, similar rates have been reported elsewhere along the southern margin of the Alaska Peninsula (Malloy, 1964;Plafker, 1965Plafker, , 1967Plafker, , 1969Plafker, , 1972Plafker and Rubin, 1978).…”

Section: Crustal Upliftsupporting

confidence: 71%

Prehistoric human settlement patterns in a tectonically unstable environment: Outer shumagin islands, southwestern alaska

Winslow

Johnson

1989

Geoarchaeology

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Human population movements into and around the outer Shumagin Islands of southwestern Alaska during the last 5000 years, and temporal gaps in Shumagin habitation correlate inversely with geologically inferred prehistoric earthquakes. Clusters of inferred seismic activity correlate with temporal gaps or with small, sparsely distributed archaeological sites; periods of relative seismic quiescence coincide with settlement florescence. Variations in terrace and archaeological site heights across the study area indicate differential uplift of the outer Shumagin Islands when corrected for the Holocene sea level rise and post-glacial isostatic adjustments. INTRODUCTIONCoastal people in tectonically active areas can be dramatically affected by co-seismic events that may include permanent uplift or subsidence, severe shaking, tilting, and inundation by large tsunamis. Major food resources such as shellfish beds can be destroyed by increased or decreased shelf depths, landslides can bury settlements, collapsing seacliffs can take settlements and boats with them, and changes in harbor geometries by creation or removal of natural barriers can make a locality more or less favorable for future habitation. Therefore, following a great earthquake, major disruption of the human record, either a hiatus or marked reduction in size of sites, might be expected (Black, 1981).The interplay between tectonic uplift or subsidence and the early Holocene sea level rise not only predicts the location of desirable coastal habitats and the maximum age of archaeological sites, but also affects preservation of former settlements (Black, 1977). Therefore, recognition of temporal and spatial patterns of crustal movements and the timing and approximate size of geologically inferred prehistoric earthquakes and tsunamis is of critical importance to the evaluation of the prehistoric archaeological record. Conversely, interpretations of long term crustal behavior must not violate human

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Section: Crustal Upliftsupporting

confidence: 71%

Prehistoric human settlement patterns in a tectonically unstable environment: Outer shumagin islands, southwestern alaska

Winslow

Johnson

1989

Geoarchaeology

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“…The Hanning Bay and Patton Bay faults had 5 and 10 m of differential vertical slip on Montague Island, respectively (Plafker, 1969), but the greatest vertical uplift was located beneath the shallow waters immediately west of Montague Island. Using bathymetric differencing techniques from pre-and postearthquake data, Malloy (1964) and Liberty et al (2013) mapped these faults to the southwest beneath the Gulf of Alaska. High-resolution sparker seismic profiles suggest the associated growth faults have remained active throughout the deposition of the Quaternary sediments .…”

Section: The 1964 Great Alaska Earthquakementioning

confidence: 99%

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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“…In our case, we examine differences between bathymetric surveys from the 1920s and regional seafloor surveys acquired in 1965 and2004 (Figure 2). Although bathymetric surveys acquired prior to modern GPS navigation contain large positioning errors, vertical and horizontal controls for the hydrography of two older surveys were considered quite strong and show a clear pattern of coseismic uplift [Malloy, 1964]. We then use new high-resolution sparker seismic reflection data that we collected to interpret the postglacial tectonic and depositional history of the area across the active splay faults (Figures 1 and 2).…”

Section: Introductionmentioning

confidence: 99%

“…First, we compare pre-and post-1964 bathymetric data from offshore Montague and Latouche Islands at the western margin of PWS to examine the uplift pattern during the 1964 earthquake. Bathymetric differencing has been used to document uplift from the 1964 Great Alaska earthquake [Malloy, 1964] and the 2011 Tohoku earthquake [Fujiwara et al, 2011]. Although Malloy used the same pre-earthquake data set as our study, their postearthquake analysis was limited to seven short profiles acquired southwest of Montague Island.…”

Section: Introductionmentioning

confidence: 99%

“…The baseline for our bathymetric differencing analysis is a relatively dense 1927-1928 survey carried out near Montague Island and north to Bainbridge Passage (Figure 2). This data set consists of approximately 8700 measured points that were depth calibrated by up and down lead line casts [Malloy, 1964]. The horizontal positions were controlled by measuring angles between prominent features on adjacent islands, and depth errors were minimal due to the lead line method.…”

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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Crustal Uplift Southwest of Montague Island, Alaska

Cited by 18 publications

References 0 publications

Prehistoric human settlement patterns in a tectonically unstable environment: Outer shumagin islands, southwestern alaska

Prehistoric human settlement patterns in a tectonically unstable environment: Outer shumagin islands, southwestern alaska

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

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

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