Appendix I

North–south-striking and west-dipping Basin and Range province normal faults form the western edge of the Sierra Madre Occidental plateau in northeastern Sonora.

We present a model for estimating horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The model provides predictive relationships for the orientation independent average horizontal component of ground motions. Relationships are provided for peak acceleration, peak velocity, and 5-percent damped pseudo-spectral acceleration for spectral periods of 0.01 to 10 seconds. The model represents an update of the relationships developed by Sadigh et al.

Seismic design requirements for critical facilities normally require the development and application of a uniform hazard spectrum having a specified return period. For a soil site, hazard results are often evaluated for bedrock level and soil surface.

A distinctive suite of volcanic, sedimentary, structural, and physiographic characteristics permits differentiation of the post-1 2- to 15- Ma Basin-Range disturbance from earlier mid-Tertiary extensional tectonism in Arizona. Basin-Range volcanism comprises basalts or bimodal basalt-rhyolite suites that are concentrated in several fields in central and northern Arizona; the age of volcanism generally decreases northeast and east onto the Colorado Plateau margin.

Paleoseismological data for the Wasatch and San Andreas fault zones have led to the formulation of the characteristic earthquake model, which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum.

Source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude (M), surface rupture length, subsurface rupture length, downdip rupture width, rupture area, and maximum and average displacement per event. The resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment, moment magnitude, subsurface rupture length, downdip rupture width, and average surface displacement.

This paper introduces a method for the evaluation of the seismic risk at the site of an engineering project. The results are in terms of a ground motion parameter (such as peak acceleration) versus average return period. The method incorporates the influence of all potential sources of earthquakes and the average activity rates assigned to them.

Sieh and Jahns (1984) forecasted that the next moderate Parkfield earthquake might trigger a major earthquake along a fault segment greater than 30 km long southeast of Cholame. Their forecast assumed (1) the slip was 3–4 m in 1857 and characteristic of the segment; (2) a slip rate of 3.4 cm/yr; and (3) full strain release in earthquakes.

The frequency of occurrence of earthquakes with different seismic moments is expressed in terms of the rate of slip on a fault and to the largest seismic moment likely to occur in the region.