STATE OF THE ART FOR ASSESSING EARTHQUAKE HAZARDS IN THE UNITED STATES; PLATE TECTONICS AND EARTHQUAKE ASSESSMENT

The emerging theory of plate tectonics, embodying continental drift, sea-floor spreading, transform faults, subduction of lithospheric plates, and other basic tenets, provides earth scientists with a reasonably coherent and workable explanation of the occurrence and distribution of earthquakes. In this report, plate boundary regimes are examined and the variable factors influencing plate interaction and earthquake generation are evaluated. These findings are applied to various boundary regimes found along the west coast of the United States. The geologic history of the United States, interpreted in terms of plate tectonics, is outlined to emphasize that crustal structures currently active in producing earthquakes had their origin long age in episodes of continental drifting and collision. The processes of orogeny and epeirogeny are examined in terms of earthquake generation. The seismicity of the United States is reviewed and related to plate tectonic phenomena currently active and to contemporary stress fields. Evidence indicates that seismicity of the western United States is the product of the interaction between the Pacific and North America plates (as a result of transform and convergent boundary regimes along the west coast) and the interaction of subplates within the western interior, the latter interaction having been mobilized by mantle plumes overridden by the North America plate. Although the present understanding of plate tectonics have provided a framework into which a wide variety of geological and geophysical observations can be fitted, plate tectonic theory is still being formulated and it is not completely understood. There are many gaps not only in the present state of knowledge of the driving mechanism but also in the knowledge of the stress conditions prevailing in the crust of the United States and how this stress is released in the form of earthquakes by plate motion.

  • Supplemental Notes:
    • This is Report 5 of a Series.
  • Corporate Authors:

    U.S. Army Waterways Experiment Station

    3909 Halls Ferry Road
    Vicksburg, MS  United States  39180-6199
  • Authors:
    • Walper, J L
  • Publication Date: 1976-3

Media Info

  • Features: Appendices; Figures; References;
  • Pagination: 106 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00139285
  • Record Type: Publication
  • Report/Paper Numbers: Miscln Papers S-73-1
  • Files: TRIS
  • Created Date: Sep 16 1976 12:00AM