Abstract
A subset of 2660 shallow earthquakes (0–50 km) that occurred from 1988 to 1996 in south central Alaska between 155°W and 145°W and 59°N and 63°N was relocated using the joint hypocenter determination (JHD) method. Both P- and S-wave observations recorded by the regional seismic network were used. Events were relocated in twenty different groups based on their geographic location and depth using two velocity models. As a result of the relocation, the majority of the hypocenters shifted downward, while the epicenter locations did not change significantly. The distribution of the shallow subduction zone earthquakes indicates the existence of two seismically independent blocks, with one block occupying the northeastern part and the other occupying the central and western parts of the study area. The boundary between the blocks is marked by a 15 to 20 km wide seismicity gap to the southeast of 149.5°W and 62°N. The analysis of the fault plane solutions for shallow subduction zone earthquakes shows that an overwhelming majority of the solutions represent normal, oblique-normal or strike-slip faulting with predominant WNW-ESE orientation of T-axes. This indicates a down-dip extensional regime for the subducting slab at shallow depths. Very few earthquakes yielded fault plane solutions consistent with thrusting on a contact zone between the overriding and subducting plates. This result may be an indication that currently either the strain energy is not released at the contact zone or it is associated with aseismic motion.
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Brocher, T. M., Fuis, G. S., Fisher, M. A., Plafker, G., Moses, M. J., Taber, J. J. and Christensen, N. I., 1994, Mapping of the megathrust beneath the northern Gulf of Alaska using wide-angle seismic data, J. Geophys. Res. 99, 11663–11685.
Chandan, K. S. and Chatterjee, D., 1997, Analysis of seismic hazard in the greater Anchorage region, Alaska due to a Mw 6.78 earthquake on the Castle Mountain fault, Seism. Res. Lett. 68, 304.
Chatterjee, D., Nath, S. K., Biswas, N. N., Dravinski, M. and Papageorgiou, A., 1997, Shear wave velocity distribution in near surface geological formation in Anchorage, Alaska, Seism. Res. Lett. 68, 312.
Christensen, D. H. and Beck, S. L., 1994, The rupture process and tectonic implications of the Great 1964 Prince William Sound earthquake, Pageoph 142, 29–53.
Douglas, A., 1967, Joint epicentre determination, Nature 215, 47–48.
Dravinski, M., Ding, G., Biswas, N. N. and Chatterjee, D., 1997, Microseism ground motion amplification in Anchorage, Alaska basin, Seism. Res. Lett. 68, 311.
Ehm, A., 1983, Oil and Gas basins map of Alaska, Alaska Div. of Geol. and Geophys. Surv. Map SR-32.
Engdahl, E. R., Dewey, J. W. and Fujita, K., 1982, Earthquake location in island arcs, Phys. Earth Planet. Int. 30, 145–156.
Fisher, M. A., Von Huene, R., Smith, G. L. and Bruns, T. R., 1983, Possible seismic reflections from the downgoing Pacific plate, 275 kilometers arcwards from the eastern Alaska-Aleutian trench, J. Geophys. Res. 88, 5835–5849.
Fogleman, K. A., Rowe, C. A. and Hammond, W. R., 1996, Alaska earthquakes-1994, in Moore, T. E. and Dumoulin, J. A. (eds), Geologic studies in Alaska by the USGS during 1994, USGS Bull. 2152, pp. 59–80.
Frohlich, C., 1992, Triangle diagrams: ternary graphs to display similarity and diversity of earthquake focal mechanisms, Phys. Earth Planet. Int. 75, 193–198.
Lahr, J. C., 1989, HYPOELLIPSE/version 2.00: A computer program for determining local earthquakes hypocentral parameters, magnitude, and first motion pattern, U.S. Geol. Surv. Open File Rep. 89–116.
Lahr, J. C., Page, R. A., Stephens, C. D. and Fogleman, K. A., 1986, Sutton, Alaska, earthquake of 1984: evidence for activity on the Talkeetna segment of the Castle Mountain fault system, Bull. Seism. Soc. Am. 76, 967–983.
Mahdyiar, M., 1997, Probabilistic seismic hazard analysis of the city of Anchorage, Alaska, Seism. Res. Lett. 68, 304.
Matumoto, T. and Page, R. A., 1969, Microaftershocks following the Alaska earthquake of 28 March 1964: Determination of hypocenters and crustal velocities in the Kenai Peninsula-Prince William Sound area, in The Prince William Sound, Alaska, earthquake of 1964 and aftershocks, U.S. Coast and Geodetic Surv. Publ. 10–3 2B&C, U.S. Govt. Printing Office, Washington, D.C., pp. 157–173.
Nath, S. K., Chatterjee, D., Biswas, N. N., Dravinski, M. and Papageorgiou, A., 1997, Determination of site amplification factor in Anchorage, Alaska in the 1–11 Hz frequency band, Seism. Res. Lett. 68, 311.
Page, R. A., Biswas, N. N., Lahr, J. C. and Pulpan, H., 1991, Seismicity of continental Alaska, in Slemmons, D. B., Engdahl, E. R., Zoback, M. D. and Blackwell, D. D. (eds), Neotectonics of North America, Boulder, Colorado, Geological Society of America, Decade Map, 1, pp. 47–68.
Page, R. A., Stephens, C. D. and Lahr, J. C., 1989, Seismicity of the Wrangell and Alaska-Aleutian Wadati-Benioff zones and the North American plate along the Trans-Alaska Crustal Transect, Chugach Mountains and Copper River basin, southern Alaska, J. Geophys. Res. 94, 16059–16082.
Papageorgiou, A. S., Zhang, B., Dong, G. and Biswas, N. N., 1997, Estimation of strong ground motion from the Great 1964 Prince William Sound earthquake (Mw =9.2), Seism. Res. Lett. 68, 325.
Pavlis, G. and Booker, J., 1983, Progressive multiple event location (PMEL), Bull. Seism. Soc. Am. 73, 1753–1777.
Plafker, G., Nokleberg, W. J. and Lull, J. S., 1989, Bedrock geology and tectonic evolution of Wrangellia, Peninsular, and Chugach terranes along the Trans-Alaska Crustal Transect in the Chugach Mountains and southern Copper River basin, J. Geophys. Res. 94, 4255–4296.
Pujol, J., 1988, Comments on the joint determination of hypocenters and station corrections, Bull. Seism. Soc. Am. 78, 1179–1189.
Pujol, J., 1996, An integrated 3D velocity inversion – Joint Hypocentral Determination relocation analysis of events in the Northridge area, Bull. Seism. Soc. Am. 86, S138–S155.
Ratchkovsky, N. A., Biswas, N. and Pujol, J., 1997a, Earthquake source zones in and around Anchorage, Alaska, Seism. Res. Lett. 68, 316.
Ratchkovsky, N. A., Pujol, J. and Biswas, N., 1997b, Relocation of events in the Cook Inlet area, south central Alaska using the Joint Hypocenter Determination method, Bull. Seism. Soc. Am. 87, 620–636.
Ratchkovsky, N. A., Pujol, J. and Biswas, N., 1997c, Stress pattern in the double seismic zone beneath Cook Inlet, south-central Alaska, Tectonophysics 281, 163–172.
Reasenberg, P. A., Oppenheimer, D., Lahr, J. C., Stephens, C. D. and Page, R. A., 1986, Alaska Project version of FPFIT, FPPLOT and FPPAGE: Fortran computer programs for calculating and displaying earthquake fault-plane solutions, U.S. Geol. Surv. Open File Rep. 86.
Stephens, C. D., Fogleman, K. A., Lahr, J. C. and Page, R. A., 1984, Wrangell Benioff zone, southern Alaska, Geology 12, 373–376.
Van Wormer, J. D., Davies, J. and Gedney, L., 1974, Seismicity and plate tectonics in south central Alaska, Bull. Seism. Soc. Am. 64, 1467–1475.
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Ratchkovsky, N.A., Pujol, J. & Biswas, N.N. Relocation of shallow earthquakes in southern Alaska using Joint Hypocenter Determination method. Journal of Seismology 2, 87–102 (1998). https://doi.org/10.1023/A:1009758721717
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DOI: https://doi.org/10.1023/A:1009758721717