Deformation in the Yakataga Seismic Gap, southern Alaska, 1980–1986

Savage, J. C.; Lisowski, M.

doi:10.1029/jb093ib05p04731

Cited by 25 publications

(15 citation statements)

References 23 publications

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“…Farther east, our model shows an average of 5.4 ± 1.8 mm/yr left‐lateral motion with 13.8 ± 6.9 mm/yr of reverse slip, although this fault segment is only partially coupled. Our prediction of left‐lateral shear along the Malaspina fault agrees with the results of Savage and Lisowksi [], who found left‐lateral shear across a zone roughly aligned with the trend of the Malaspina fault through Icy Bay.…”

Section: Discussionsupporting

confidence: 91%

“…None of the faults in our model have published geodetic or geologic slip rate estimates. Previous models of the St. Elias orogen [e.g., Sauber et al ., ; Savage and Lisowski , ] have usually assumed that the main source of the regional deformation is strain accumulation along a subduction interface that is slipping at a rate equal to the Pacific plate–North America relative velocity. This rate of motion was 50–60 mm/yr, depending on the plate motion model used [e.g., Minster and Jordon , ; Chase , ; DeMets et al ., ].…”

Section: Discussionmentioning

confidence: 99%

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Active tectonics of the St. Elias orogen, Alaska, observed with GPS measurements

2013

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[1] We use data from campaign and continuous GPS sites in southeast and south central Alaska to constrain a regional tectonic block model for the St. Elias orogen. Active tectonic deformation in the orogen is dominated by the effects of the collision of the Yakutat block with southern Alaska. Our results indicate that~37 mm/yr of convergence is accommodated along a relatively narrow belt of N-NW dipping thrust faults in the eastern half of the orogen, with the present-day deformation front running through Icy Bay and beneath the Malaspina Glacier. Near the Bering Glacier, the collisional thrust fault regime transitions into a broad, northwest dipping décollement as the Yakutat block basement begins to subduct beneath the counterclockwise rotating Elias block. The location of this transition aligns with the Gulf of Alaska shear zone, implying that the Pacific plate is fragmenting in response to the Yakutat collision. Our model indicates that the Bering Glacier region is undergoing internal deformation and could correspond to the final stage of offscraping and accretion of sediments from the Yakutat block prior to subduction. Predicted block motions at the western edge of the orogen suggest that the crust is laterally escaping along the Aleutian fore arc.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Active tectonics of the St. Elias orogen, Alaska, observed with GPS measurements

2013

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“…The ongoing rate of tectonic deformation over the last 20 years has been estimated from trilateration, very-long-baseline interferometry (VLBI) and GPS measurements [Savage and Lisowski, 1988;Ma et al, 1990;Sauber et al, 1993Sauber et al, , 1997. The rate and orientation of tectonic stress and strain is due primarily to subduction of the Pacific plate and collision of the Yakutat terrane with interior Alaska (Figure 2).…”

Section: Tectonic Stress and Strain Orientation And Magnitudementioning

confidence: 99%

Glacier ice mass fluctuations and fault instability in tectonically active Southern Alaska

Sauber

Molnia

2004

Global and Planetary Change

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Across southern Alaska the northwest directed subduction of the Pacific plate is accompanied by accretion of the Yakutat terrane to continental Alaska. This has led to high tectonic strain rates and dramatic topographic relief of more than 5000 meters within 15 km of the Gulf of Alaska coast. The glaciers of this area are extensive and include large glaciers undergoing wastage (glacier retreat and thinning) and surges. The large glacier ice mass changes perturb the tectonic rate of deformation at a variety of temporal and spatial scales. We estimated surface displacements and stresses associated with ice mass fluctuations and tectonic loading by examining GPS geodetic observations and numerical model predictions. Although the glacial fluctuations perturb the tectonic stress field, especially at shallow depths, the largest contribution to ongoing crustal deformation is horizontal tectonic strain due to plate convergence. Tectonic forces are thus the primary force responslble for major eartnquakes. Xowever, for geodefic sites located < 10-20 km from major ice mass fluctuations, the changes of the solid Earth due to ice loading and unloading are an important aspect of interpreting geodetic results.The ice changes associated with Bering Glacier's most recent surge cycle are large enough to cause discernible surface displacements. Additionally, ice mass fluctuations associated with the surge cycle can modify the shod-term seismicity rates in a local region. For the thrust faulting environment of the study region a large decrease in ice load may cause an increase in seismic rate in a region close to failure whereas ice loading may inhibit thrust faulting.Prior to the 1979 St. Elias earthquake (M=7.2), the main thrust zone below the study region had been locked since the 1899 earthquakes and strain had been accumulating. During this same time period ongoing wastage of southern Alaska glaciers was 100's of meters up to almost a 1 km. We used estimates of ice thickness decrease to calculate the changes in the fault stability margin around the region of the 1979 St. Elias earthquake and aftershocks. Our results suggest that the cumulative decrease in the fault stability margin due to ice wastage between 1899 and 1979 was large and would promote thrust faulting. Since earthquake hazard evaluations are based on the paleoseismic history of the region, for glaciated areas the concurrent glacial history should be considered in this evaluation. Glacier terminus. In addition to modifying the surface displacements rates, we evaluated the influence ice changes during the Bering glacier surge cycle had on the background seismic rate.We found an increase in the number of earthquakes (ML 2 2.5) and seismic rate associated with ice thinning and a decrease in the number of earthquakes and seismic rate associated with ice thickening. These results support the hypothesis that ice mass changes can modulate the background seismic rate.

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“…ΔCFF uncertainty ±10 kPa. References: 1, Plafker et al [1994]; 2, Lahr et al [1986]; 3, Savage and Lisowski [1988]; 4, Richter and Matson [1971].…”

Section: Combined Effect Of Nm and Df Events On Regional Fault Systemsmentioning

confidence: 99%

Static stress transfer during the 2002 Nenana Mountain‐Denali Fault, Alaska, earthquake sequence

Anderson

2003

Geophysical Research Letters

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On 23 October 2002, the Mw 6.7 Nenana Mountain earthquake occurred in central Alaska. It was followed on 3 November 2002 by the Mw 7.9 Denali Fault mainshock, the largest strike‐slip earthquake to occur in North America during the past 150 years. We have modeled static Coulomb stress transfer effects during this sequence. We find that the Nenana Mountain foreshock transferred 30–50 kPa of Coulomb stress to the hypocentral region of the Denali Fault mainshock, encouraging its occurrence. We also find that the two main earthquakes together transferred more than 400 kPa of Coulomb stress to the Cross Creek segment of the Totschunda fault system and to the Denali fault southeast of the mainshock rupture, and up to 80 kPa to the Denali fault west of the Nenana Mountain rupture. Other major faults in the region experienced much smaller static Coulomb stress changes.

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Deformation in the Yakataga Seismic Gap, southern Alaska, 1980–1986

Cited by 25 publications

References 23 publications

Active tectonics of the St. Elias orogen, Alaska, observed with GPS measurements

Active tectonics of the St. Elias orogen, Alaska, observed with GPS measurements

Glacier ice mass fluctuations and fault instability in tectonically active Southern Alaska

Static stress transfer during the 2002 Nenana Mountain‐Denali Fault, Alaska, earthquake sequence

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