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


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.


  1. Altstatt, A. A., R. W. Saltus, R. L. Bruhn, and P. J. Haeussler, Magnetic susceptibilities measured on rocks of the upper Cook Inlet, Alaska, U.S. Geological Survey Open-File Report 02-0139, 17 pp., [], 2002.

  2. Anonymous, Cook Inlet basin still holds some exploration, development allure, Oil and Gas Journal, 99(10), 43, 1999.

  3. Atwater, B. F. and E. Hemphill-Haley, Recurrence intervals for great earthquakes of the past 3500 years at northeastern Willapa Bay, Washington, U.S. Geological Survey Professional Paper 1576, 108 pp., 1997.

  4. Barnes, D. F., Bouguer gravity map of Alaska, U.S. Geological Survey Map GP-913, scale 1:2,500,000, 1 sheet., 1977.

  5. Blakely, R. J., R. E. Wells, and C. S. Weaver, Puget Sound aeromag-netic maps and data, U.S. Geological Survey Open-File Report 99–514,, 1999.

  6. Blakely, R. J., R. E. Wells, C. S. Weaver, and S. Y. Johnson, Location, structure, and seismicity of the Seattle fault zone, Washington: Evidence from aeromagnetic anomalies, geologic mapping, and seismic-reflection data, Geological Society of America Bulletin, 114, 169–177, 2002.

  7. Blakely, R. J., T. M. Brocher, and R. E. Wells, Subduction zone magnetic anomalies and implications for hydrated forearc mantle, Geology, 33, 445–448, 2005.

  8. Blakely, R. J., B. L. Sherrod, R. E. Wells, C. S. Weaver, D. H. McCor-mack, K. G. Troost, and R. A. Haugerud, The Cottage Lake aeromagnetic lineament: A possible onshore extension of the southern Whid-bey Island fault, Washington, U.S. Geological Survey Open-File Report 2004-1204, 61 pp.

  9. Bostock, M. G., R. D. Hyndman, S. Rondenay, and S. M. Peacock, An inverted continental Moho and serpentinization of the forearc mantle, Nature, 417, 536–538, 2002.

  10. Brocher, T. M., R. J. Parsons, R. J. Blakely, N. I. Christensen, M. A. Fisher, R. E. Wells, and the SHIPS Working Group, Upper crustal structure in Puget Lowland, Washington: Results from the 1998 Seismic Hazards Investigation in Puget Sound, Journal of Geophysical Research, 106, 13,541–13,564, 2001.

  11. Brocher, T. M., T. Parsons, A. M. Tréhu, C. M. Snelson, and M. A. Fisher, Seismic evidence for widespread serpentinized forearc upper mantle along the Cascadia margin, Geology, 31, 267–270, 2003.

  12. Brocher, T. M., R. J. Blakely, and R. E. Wells, Interpretation of the Seattle Uplift, Washington, as a passive roof duplex, Bulletin of the Seismolog-ical Society of America, 94(4), 1379–1401, 2004.

  13. Bucknam, R. C., E. Hemphill-Halley, and E. B. Leopold, Abrupt uplift within the past 1700 yr at southern Puget Sound, Washington, Science, 258, 1611–1614, 1992.

  14. Christensen, D. H. and S. L. Beck, The rupture process and tectonic implications of the great 1964 Prince William Sound earthquake, Pure and Applied Geophysics, 142, 29–53, 1994.

  15. Combellick, R. A., Paleoseismicity of the Cook Inlet region, Alaska: Evidence from peat stratigraphy in Turnagain and Knik Arms, Alaska Division of Geological and Geophysical Surveys Professional Report 112, 52 pp., 1991.

  16. Combellick, R. A., The penultimate great earthquake in southcentral Alaska: Evidence from a buried forest near Girdwood, Short notes on Alaskan geology 1993, edited by D. N. Solie and F. Tannian, Alaska Division of Geological and Geophysical Surveys Professional Report 113, pp. 7–15, 1993.

  17. Combellick, R. A., Investigations of peat stratigraphy in tidal marshes along Cook Inlet, Alaska, to determine the frequency of 1964-style great earthquakes in the Anchorage region, Alaska Division of Geological and Geophysical Surveys Report of Investigations 94–7, 24 pp., 1994.

  18. Finn, C., Geophysical constraints on Washington convergent margin structure, Journal of Geophysical Research, 95, 19,533–19,546, 1990.

  19. Frankel, A. D., D. L. Carver, and R. A. Williams, Nonlinear and linear site response and basin effects in Seattle for the M 6.8 Nisqually, Washington, earthquake, Bulletin of the Seismological Society of America, 92, 2090–2109, 2002.

  20. Gardner, G. H. F., L. W. Gardner, and A. R. Gregory, Formation velocity and density: the diagnostic basics for stratigraphic traps, Geophysics, 39, 770–780, 1974.

  21. Grantz, A., I. Zeitz, and G. E. Andreasen, An Aeromagnetic Reconnaissance of the Cook Inlet Area Alaska, U.S. Geological Survey Professional Paper 316-G, pp. 117–134, 1963.

  22. Grauch, V. J. S., High-resolution aeromagnetic data, a new tool for mapping intrabasinal faults: Example from the Albuquerque basin, New Mexico, Geology, 29, 367–370, 2001.

  23. Griscom, A. and J. E. Case, Magnetic expression of geologic terranes in southern Alaska, Geophysics, 48, 444–445, 1983.

  24. Haeussler, P. J. and R. W. Saltus, Location, extent, and estimates of deformation rates of Tertiary structures in the Cook Inlet basin, Alaska, U.S. Geological Survey Open-File Report 04-XXX, XX pp., [], in review (a).

  25. Haeussler, P. J. and R. W. Saltus, Lahars as aeromagnetic anomaly sources, Cook Inlet, Alaska, U.S. Geological Survey Open-File Report, in review (b).

  26. Haeussler, P. J., R. L. Bruhn, and T. L. Pratt, Potential seismic hazards and tectonics of the upper Cook Inlet basin, Alaska, based on analysis of Pliocene and younger deformation, Geological Society of America Bulletin, 112(9), 1414–1429, 2000.

  27. Hyndman, R. D. and K. Wang, The rupture zone of Cascadia great earthquakes from current deformation and the thermal regime, Journal of Geophysical Research, 100, 22,133–22,154, 1995.

  28. Johnson, S. Y., C. J. Potter, and J. M. Armentrout, Origin and evolution of the Seattle fault and Seattle basin, Washington, Geology, 22, 71–74, 1994.

  29. Johnson, S. Y., C. J. Potter, J. M. Armentrout, J. J. Miller, C. Finn, and C. S. Weaver, The southern Whidbey Island fault: An active structure in the Puget lowland, Washington, Geological Society of America Bulletin, 108, 334–354, 1996.

  30. Kirby, S., E. R. Engdahl, and R. Denlinger, Intermediate-depth intraslab earthquakes and arc volcanism as physical expressions of crustal and uppermost mantle metamorphism in subducting slabs, in Subduction: Top to Bottom, edited by G. E. Bebout et al., pp. 195–214, American Geophysical Union Monograph 96, 1996.

  31. Kirschner, C. E. and C. A. Lyon, Stratigraphic and tectonic development of Cook Inlet petroleum province, in Arctic Geology, pp. 396–407, American Association of Petroleum Geologists Memoir 19, 1973.

  32. Magoon, L. B., Petroleum resources in Alaska, in The Geology of Alaska, The Geology of America, edited by G. Plafker and H. C. Berg, v. G-1, pp. 905–936, Geological Society of America, 1994.

  33. Magoon, L. B. and R. M. Egbert, Framework geology and sandstone composition, Geologic studies of the lower Cook Inlet COST No. 1 well, Alaska outer continental shelf, edited by L. B. Magoon, U.S. Geological Survey Bulletin, 1596, 65–90, 1986.

  34. Magoon, L. B., W. L. Adkison, and R. M. Egbert, Map showing geology, wildcat wells, Tertiary plant fossil localities, K-Ar age dates, and petroleum operations, Cook Inlet area, Alaska, U.S. Geological Survey Map I-1019, scale 1:250,000, 3 sheets, 1976.

  35. Nelson, A. R., S. Y. Johnson, H. M. Kelsey, R. E. Wells, B. L. Sherrod, S. K. Pezzopane, L. A. Bradley, R. D. Koehler, III, and R. C. Bucknam, Late Holocene earthquakes on the Toe Jam Hill fault, Seattle fault zone, Bainbridge Island, Washington, Geological Society of America Bulletin, 115, 1388–1403, 2003.

  36. Phillips, J. D., Potential-field geophysical software for the PC—version 2.2, U.S. Geological Survey Open-File Report 97–725, 34 pp. [], 1997.

  37. Plafker, G., Tectonic deformation associated with the 1964 Alaska earthquake, Science, 148, 1675–1687, 1965.

  38. Pratt, T. L., S. Johnson, C. Potter, W. Stephenson, and C. Finn, Seismic reflection images beneath Puget Sound, western Washington State: The Puget Lowland thrust sheet hypothesis, Journal of Geophysical Research, 102, 27,469–27,489, 1997.

  39. Saltus, R. W. and P. J. Haeussler, Magnetic properties of Quaternary deposits, Kenai Peninsula, Alaska—Implications for aeromagnetic anomalies in upper Cook Inlet, U.S. Geological Survey Open-File Report 2004–1202, 26 pp., [], 2004.

  40. Saltus, R. W., P. J. Haeussler, R. E. Bracken, J. P. Doucette, and R. C. Jachens, Anchorage Urban Region Aeromagnetics (AURA) Project—Preliminary Geophysical Results, U.S. Geological Survey Open-File Report 01-0085, 21 pp., [], 2001.

  41. Syberg, F. J. R., A Fourier method for the regional-residual problem of potential fields, Geophysical Prospecting, 20, 47–75, 1972.

  42. Wells, R. E., C. S. Weaver, and R. J. Blakely, Fore-arc migration in Casca-dia and its neotectonic significance, Geology, 26, 759–762, 1998.

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Correspondence to R. W. Saltus.

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Key words

  • Aeromagnetic
  • susceptibility
  • seismic hazards