Local Tectonic Setting

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Clearly identifying and determining the activity level of faults within and adjacent to a project region is critical for development of the input parameters required to perform an SHA. An experienced seismologist should assess and summarize available literature to identify known seismic conditions in a region. The record of historical earthquakes should be evaluated to develop and verify recurrence parameters for known faults.

Paleoseismicity evaluations are used to supplement seismic monitoring in calculating the seismic hazard of a location. Paleoseismologic reports should be evaluated, or new investigations conducted, to refine the local seismic setting. Paleoseismologic investigations assess the sediments and rocks of an area for indications of ancient and recent earthquakes. Such explorations are usually restricted to geologic regimes that have undergone continuous sedimentation over the last few thousand years, such as swamps, lakes, river beds and shorelines.

Paleoseismic exploration often uses trenching to determine the activity of faults in specific locales. Trenching helps develop parameters needed in modeling faults. In a typical example, a trench is dug across the trace of a suspected active fault in an area of active sedimentation. An experienced geologist can potentially identify evidence of the recency of fault displacement in the walls of the trench. The relative age for the most recent displacement of a fault may be deduced through careful evaluation of cross-cutting fracture and sedimentation patterns. Faults may also be age-dated in absolute terms if dateable carbon or human artifacts are present.

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Revision ID: 5769
Revision Date: 12/14/2022