Fault Sources
From ASDSO Dam Safety Toolbox
Fault sources are modeled as multi-planar features with earthquake ruptures distributed over the fault plane. The input parameters required to model a fault in a Seismic Hazard Analysis (SHA) are as follows:
- Fault Geometry: The fault geometry includes the coordinates in map view, cross-section (depth), width, and the dip.
- Mechanism: Each fault should have a specified mechanism: normal, reverse (thrust) or strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement involves a vertical component. Normal faults occur mainly in areas where the crust is being extended such as divergent boundaries. Reverse (thrust) faults occur in areas where the crust is being shortened for example at convergent boundary. Strike-slip faults are normally steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.
- Magnitude Distribution: The magnitude distribution is a probability density function (pdf) that describes the relative number of large magnitude, moderate and small magnitude earthquakes that occur on a seismic source. There are two forms of the magnitude density functions that are considered in Probabilistic Seismic Hazard Analysis (PSHA). The functions are a truncated exponential model and the characteristic model. Alternate models are composites of the truncated exponential and the characteristic. This parameter is only required for Probabilistic Seismic Hazard Analysis.
- Activity Rate: There are two common approaches for estimating activity rates on seismic sources: historical seismicity and geologic information. This parameter is only required for PSHA.
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Revision ID: 6704
Revision Date: 03/17/2023