Seismic source characterization

DOE-STD-1022-94

Fault Segmentation. Fault zones usually consist of individual fault segments. Fault segmentation

provides a means for estimating the expected length of fault ruptures. The locations of fault segments and

the boundaries between segments shall be evaluated.

5. Source-to-site distance. The factors described above, which govern the location and geometry of seismic

sources, provide the basis for establishing the distance between the site and the earthquake source. The

measure of the source-to-site distance used in the seismic hazard analysis (e.g., epicentral distance or

closest distance to the fault rupture surface) may vary depending upon the procedure used to estimate

earthquake attenuation effects.

5.4.1.2 Seismic source characterization

A. The ranges of potential seismic sources and the uncertainties in seismicity parameters should be defined as

required in DOE-STD-1023-95.

B. The characteristics of a seismic source may include:

Source zone geometry (location and extent, both surface and subsurface),

Description of Quaternary displacements (sense of slip on the fault, fault dimensions, age of

displacement, estimated displacement per event, estimated magnitudes per offset, rupture length and area,

and displacement history or uplift rates of seismogenic folds),

Historical and instrumental seismicity associated with each source,

Paleoseismicity,

Relationship of the fault to other potential seismic sources in the region,

Maximum earthquake the source would be capable of producing,

Recurrence model (frequency of earthquake occurrence versus magnitude).

C. Maximum earthquakes are usually assessed in two principal ways:

1. Estimate the maximum dimensions of future ruptures and relate those dimensions to magnitude. This

approach, which is geared toward characterizing the dimensions of faults, is commonly applied in the

WUS. The dimensions of ruptures and/or amount of displacement that might be expected on a fault of

interest are estimated from geologic investigations designed to assess what has occurred during past

ruptures. As many of the rupture dimensions as possible should be used to lend stability to the magnitude

estimates. Also, the uncertainties in the values of the rupture parameters should be incorporated (e.g.,

National Research Council, 1988; Coppersmith and Youngs, 1986; 1990).

2. Consider the size of historical earthquakes associated with the source and with tectonically-analogous

sources. However, this approach should only be applied after it has been shown that the approach

commonly used in the WUS as described above is not applicable. Common acceptable approaches used

in assessing maximum earthquakes in the Eastern United States (EUS) are: (1) take the source zone's

maximum historical earthquake as the maximum; (2) take the maximum historical earthquake and add

an arbitrary magnitude (or intensity) increment to it; or (3) draw an analogy to another source zone and

use the maximum historical earthquake associated with that source. The maximum earthquakes can also

be evaluated based on the opinions provided by a panel of experts with knowledge of the site region

(Bernreuter et al., 1989; Coppersmith and Youngs, 1990).