Anchorage Urban Region Aeromagnetics (AURA) Project — Preliminary geophysical results

Saltus, R.W.; Haeussler, Peter J.; Bracken, Robert E.; Doucette, Jon; Jachens, Robert C.

doi:10.3133/ofr0185

Cited by 10 publications

(21 citation statements)

References 12 publications

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“…4). The low pass fi ltered map shown in Figure 7 supports the hypothesis that the south Alaska magnetic high may correlate with fl uid serpentinization of the altered lower forearc crust and/or mantle at 16-34 km depth (Saltus et al, 2001;Hyndman and Peacock, 2003). Shallow sediments and rocks (<15 km) are not a likely source of the magnetic highs because high pass fi ltered maps show no broadly strong magnetic highs (Fig.…”

Section: Magnetic Anomaly Interpretationssupporting

confidence: 67%

“…The magnetic intensity highs to the west of Cook Inlet are likely related to intrusive and extrusive bodies associated with the active volcanic arc (Figs. 1 and 4) (Saltus et al, 2001). A linear contact between the long-wavelength highs of Cook Inlet and these smaller highs of the arc occurs at the position of the Bruin Bay fault.…”

Section: Magnetic Anomaly Interpretationsmentioning

confidence: 94%

“…We then used the updated geophysical potential fi eld data to construct 2D density-magnetization cross-section models. Other geological and geophysical data (e.g., well logs, seismic tomography, and surfi cial geology) were used to help constrain the model parameters and address problems of non-uniqueness related to tradeoffs between modeled thicknesses, depths, densities, and magnetic susceptibilities in order to minimize model uncertainties (Saltus et al, 2001). We also compared our results to geological processes found in other, well-studied subduction zones, such as serpentinization and underplating of sediments, to help explain the possible causes of anomalies present in our new interpretations.…”

Section: Introductionmentioning

confidence: 99%

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Interpretation of gravity and magnetic data and development of two-dimensional cross-sectional models for the Border Ranges fault system, south-central Alaska

2013

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Extensive Quaternary glacial cover and a lack of dense geophysical data within the Cook Inlet basin (CIB) of south-central Alaska make locating and determining the geometry of the Border Ranges fault system (BRFS), a major feature of the AlaskaAleutian forearc region, diffi cult. We use recently collected gravity data, available aeromagnetic data, and other geophysical information as constraints to develop plausible two-dimensional cross-section models that better image the BRFS and related geologic structures of the CIB. Our integrated models show a thick sequence of late Mesozoic sedimentary rocks and the Peninsular terrane basement (6-20 km depth) overlying a serpentinized body at a depth of 16-34 km. The late Mesozoic rocks and serpentinite are interpreted as possible sources of the south Alaska magnetic high over the CIB. The eastern boundaries of the CIB are characterized by gravity and magnetic highs of the emplaced Border Range ultramafi c and mafi c assemblages (BRUMA). Formation of the BRUMA may be related to the serpentinized rocks that composed a Jurassic oceanic arc. Our models constrain the BRFS as a structural boundary between the overthrusted BRUMA and the Chugach terrane to the east. The BRFS dips 50°-70° toward the west-northwest and extends to at least 15 km. The BRFS may penetrate steeply or shallowly to a form a décollement at greater depths. A model that includes underplated sediments at the base of the accretionary complex (12-40 km) is consistent with the observed gravity low over the Chugach Mountains (Chugach terrane). The underplating may be associated with the subducting and shortening of the Yakutat microplate in south-central Alaska.

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Section: Magnetic Anomaly Interpretationssupporting

confidence: 67%

Section: Magnetic Anomaly Interpretationsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Interpretation of gravity and magnetic data and development of two-dimensional cross-sectional models for the Border Ranges fault system, south-central Alaska

2013

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“…valuable in recognizing shallow crustal structures in both the Puget Lowland and in Cook Inlet (e.g., Blakely et al, 1999Blakely et al, , 2002Blakely et al, , 2004Saltus et al, 2001). In this paper we make a comparative examination of aeromagnetic data from Puget Sound and Cook Inlet and find remarkable similarities in aeromagnetic anomalies measured in both regions.…”

Section: Introductionmentioning

confidence: 98%

“…12) shows a number of similar shallow-source anomalies, including many linear features with trends more or less parallel to the long axis of the Cook Inlet basin. Some of these features, such as the distinctive set of curvilinear features surrounding a magnetic low in the Beluga oil and gas field region, are clearly related to shallow structure seen in seismic data (Haeussler et al, 2000;Saltus et al, 2001;Haeussler and Saltus, in review (a)). Other linear trends, such as those located further to the east over the Kenai Peninsula, may relate to monoclines or other structural or stratigraphic features.…”

Section: Aeromagnetic Data and Analysismentioning

confidence: 99%

Utility of aeromagnetic studies for mapping of potentially active faults in two forearc basins: Puget Sound, Washington, and Cook Inlet, Alaska

et al. 2005

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High-resolution aeromagnetic surveys over forearc basins can detect faults and folds in weakly magnetized sediments, thus providing geologic constraints on tectonic evolution and improved understanding of seismic hazards in convergent-margin settings. Puget Sound, Washington, and Cook Inlet, Alaska, provide two case histories. In each lowland region, shallow-source magnetic anomalies are related to active folds and/or faults. Mapping these structures is critical for understanding seismic hazards that face the urban regions of Seattle, Washington, and Anchorage, Alaska. Similarities in aeromagnetic anomaly patterns and magnetic stratigraphy between the two regions suggest that we can expect the aeromagnetic method to yield useful structural information that may contribute to earth-hazard and energy resource investigations in other forearc basins.

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The 2015 landslide and tsunami in Taan Fiord, Alaska

Higman

Shugar

Stark

et al. 2018

Sci Rep

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112

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Glacial retreat in recent decades has exposed unstable slopes and allowed deep water to extend beneath some of those slopes. Slope failure at the terminus of Tyndall Glacier on 17 October 2015 sent 180 million tons of rock into Taan Fiord, Alaska. The resulting tsunami reached elevations as high as 193 m, one of the highest tsunami runups ever documented worldwide. Precursory deformation began decades before failure, and the event left a distinct sedimentary record, showing that geologic evidence can help understand past occurrences of similar events, and might provide forewarning. The event was detected within hours through automated seismological techniques, which also estimated the mass and direction of the slide - all of which were later confirmed by remote sensing. Our field observations provide a benchmark for modeling landslide and tsunami hazards. Inverse and forward modeling can provide the framework of a detailed understanding of the geologic and hazards implications of similar events. Our results call attention to an indirect effect of climate change that is increasing the frequency and magnitude of natural hazards near glaciated mountains.

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Anchorage Urban Region Aeromagnetics (AURA) Project — Preliminary geophysical results

Cited by 10 publications

References 12 publications

Interpretation of gravity and magnetic data and development of two-dimensional cross-sectional models for the Border Ranges fault system, south-central Alaska

Interpretation of gravity and magnetic data and development of two-dimensional cross-sectional models for the Border Ranges fault system, south-central Alaska

Utility of aeromagnetic studies for mapping of potentially active faults in two forearc basins: Puget Sound, Washington, and Cook Inlet, Alaska

The 2015 landslide and tsunami in Taan Fiord, Alaska

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