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Titolo:
Crustal deformation associated with glacial fluctuations in the eastern Chugach Mountains, Alaska
Autore:
Sauber, J; Plafker, G; Molnia, BF; Bryant, MA;
Indirizzi:
NASA, Goddard Space Flight Ctr, Geodynam Branch, Greenbelt, MD 20771 USA NASA Greenbelt MD USA 20771 Ctr, Geodynam Branch, Greenbelt, MD 20771 USA ASHTECH, Reston, VA 20191 USA ASHTECH Reston VA USA 20191ASHTECH, Reston, VA 20191 USA US Geol Survey, Reston, VA 20192 USA US Geol Survey Reston VA USA 20192US Geol Survey, Reston, VA 20192 USA US Geol Survey, Menlo Park, CA 94025 USA US Geol Survey Menlo Park CA USA94025 l Survey, Menlo Park, CA 94025 USA
Titolo Testata:
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
fascicolo: B4, volume: 105, anno: 2000,
pagine: 8055 - 8077
SICI:
0148-0227(20000410)105:B4<8055:CDAWGF>2.0.ZU;2-7
Fonte:
ISI
Lingua:
ENG
Soggetto:
SOUTH CENTRAL ALASKA; BERING GLACIER; GEODETIC MEASUREMENT; 1987-1988 GULF; FINITE-ELEMENT; UPPER-MANTLE; SEA-LEVEL; EARTHQUAKE; UPLIFT; STRAIN;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
79
Recensione:
Indirizzi per estratti:
Indirizzo: Sauber, J NASA, Goddard Space Flight Ctr, Geodynam Branch, Code 921, Greenbelt, MD 20771 USA NASA Code 921 Greenbelt MD USA 20771 21, Greenbelt, MD 20771 USA
Citazione:
J. Sauber et al., "Crustal deformation associated with glacial fluctuations in the eastern Chugach Mountains, Alaska", J GEO R-SOL, 105(B4), 2000, pp. 8055-8077

Abstract

The changes of the solid Earth in south central Alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region. During the recent (1993-1995) BeringGlacier surge, a large transfer of ice from the Bagley Ice Field to the Bering Glacier terminus region occurred. We estimated the elastic displacement of the solid Earth due to ice mass redistribution from Global PositioningSystem (GPS) measurements at sites near the surging glacier. We can account for these displacements by transfer of an ice volume of about 14 km(3) from the surge reservoir area to the terminus region. We examined the background seismicity (M-L greater than or equal to 2.5) before, during, and afterthe surge. We found that the occurrence of small earthquakes (M-L less than or equal to 4.0) in the surge reservoir region increased during the surgetime interval possibly in response to a decrease in ice mass. This suggests that a Small decrease in the vertical stress, sigma(3), could be enough to modulate the occurrence of small, shallow earthquakes in this dominantly thrust fault setting. During this century the southern Alaska coastal glaciers have been undergoing an overall decrease in volume. Based on our compilation of changes in the extent and thickness of the coastal glaciers between the Malaspina and Bering, we calculated surface displacements due to the Earth's viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years. The uplift of the region due to an average annual thinning rate of 1-6 m/yr in the ablation region is 1-12 mm/yr. For ourreference model with a viscosity of 5 x 10(19) Pa s for depths between approximate to 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near Icy Bay. The maximum decrease in sigma(V) between 0and 10 km was approximate to 1.0 MPa, which is significant in relation to the stress drops in recent earthquakes (approximate to 2 to 10 MPa) but small in relation to the estimated tectonic stress magnitude. Therefore the occurrence of an earthquake such as the St. Elias (1979, M-S = 7.2) may have been advanced in time; however, most of the ongoing stress accumulation would be primarily due to tectonic forces.

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Documento generato il 05/07/20 alle ore 13:27:11