Walter J. Silva

Both the point- and finite-source stochastic ground motion models represent recent and promising developments in the quantification of strong ground motions for engineering design.

A computer code (RASCAL) has been developed to provide realistic predictions of ground motion parameters for applications to earthquake engineering risk assessment.

A formulation extending the Haskell-Thompson matrix method to include the effects of anelastic attenuation is presented. The formulation is exact in that no low-loss approximations are made. Consideration is given to nonparallel propagation and attenuation directions with corresponding velocity anisotropy. Examples are presented for models representing soils, the crust, and the core-mantle boundary.

We develop recommendations for design spectra at two sites, one in the Mojave desert, California, and the second at Columbia, South Carolina. These sites were chosen because local, small earthquakes dominate the high frequencies (f⩾10 Hz), but large distant events dominate the low frequencies (f⩽1 Hz).

Recommendations for seismic design ground motions for nuclear facilities require a consistency with both observed strong motion data and with seismological theory on the characteristics of strong shaking. Different recommendations are appropriate for various regions of the US, because both earthquake source characteristics differ and the earth's crustal properties vary with region.

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.

In previous ground-motion models, the range of applicability of the empirical ground-motion models was based on the range covered by the available empirical data set; however, in hazard studies, the ground motion must be computed for all relevant earthquakes, so the limits on the range of applicability were often ignored. To address this issue, the Next Generation Attenuation (NGA) project required the developers of the models to extrapolate their models such that they are applicable to all crustal earthquakes relevant for seismic hazard analyses in California.

Using a database of 655 recordings from 58 earthquakes, empirical response spectral attenuation relations are derived for the average horizontal and vertical component for shallow earthquakes in active tectonic regions. A new feature in this model is the inclusion of a factor to distinguish between ground motions on the hanging wall and footwall of dipping faults.

This report presents the results of sitespecific probabilistic seismic hazard analyses (PSHA) and deterministic seismic hazard analyses (DSHA) of four sites for the RMC tailings storage facilities options in southern Arizona.

Email Address Created for Land Exchange Questions

The Southwestern Region Office of Lands and Minerals Management is overseeing and administering the land exchange and appraisal process which includes the 2,422-acre Oak Flat Federal Parcel. All questions about the land exchange and appraisal process should be emailed to

Programmatic Agreement Info

To comply with Section 106 of the National Historic Preservation Act, the Tonto National Forest developed a Programmatic Agreement (PA) and included it in Volume 5, Appendix O of the final EIS. The PA was created in cooperation with the Advisory Council on Historic Preservation, the State Historic Preservation Office, tribes and other consulting parties. The PA contains an agreed upon process for identifying, evaluating and addressing adverse effects to historic properties associated with this undertaking.

To review Volume 5 and the PA, Download Vol 5 PDF, 27 MB.

Forest Service Point of Contact

John Scaggs
Tonto National Forest

Apache Leap Special Management Area
Apache Leap SMA website