Global Geologic Setting and Plate Tectonics

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A seismic hazard assessment should include an evaluation of the global geologic setting. Understanding the behavior and properties of the Earth's surface and underlying layers sets the stage for interpreting the local geologic setting.

Global tectonics is the theory that the earth’s relatively low density crust (lithosphere) is composed of seven or eight major and several smaller rigid fragments. These tectonic plates, both continental and oceanic forms of the crust, move about the earth’s face, driven by convective activity within the higher density and relatively plastic mantle (asthenosphere).

Plates interact at convergent (collisional), divergent (spreading), and transform (lateral) boundaries. Mountains rise and the sea floor is subducted in deep trenches along collisional boundaries, continents and oceans rift and open along spreading center boundaries, while continental and oceanic crust moves laterally along transform boundaries. Earthquakes and volcanic activity occur in association with these plate margins.

Research into regional tectonic conditions should be conducted at the beginning of an SHA to establish the regional seismic framework. It is important to obtain the most recent publications, as the science is dynamic and new information becomes available frequently. Information regarding the global geologic and plate tectonic setting can be obtained from governmental geological agencies for countries of the region. The U.S. Geological Survey (USGS) is a good starting point for any location.

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Revision ID: 5767
Revision Date: 12/14/2022