Development of Earthquake Ground Motion Input for Preclosure Seismic Design and Postclosure Performance Assessment of a Geologic Repository at Yucca Mountain, NV

Abstract

performed the ground motion calculations. Richard Lee and Rajendram Arulnathan assisted in the model validation. Gabriel Toro developed the site-specific probabilistic representation of the seismic velocity profiles. Susan Olig managed the software quality assurance aspects for the study. Richard Quittmeyer, and Carl Stepp assisted in the writing of the AMR. EXECUTIVE SUMMARYThis report describes a site-response model and its implementation for developing earthquake ground motion input for preclosure seismic design and postclosure assessment of the proposed geologic repository at Yucca Mountain, Nevada. The model implements a random-vibration theory (RVT), one-dimensional (1D) equivalent-linear approach to calculate site response effects on ground motions. The model provides results in terms of spectral acceleration including peak ground acceleration, peak ground velocity, and dynamically-induced strains as a function of depth. In addition to documenting and validating this model for use in the Yucca Mountain Project, this report also describes the development of model inputs, implementation of the model, its results, and the development of earthquake time history inputs based on the model results.The purpose of the site-response ground motion model is to incorporate the effects on earthquake ground motions of (1) the approximately 300 m of rock above the emplacement levels beneath Yucca Mountain and (2) soil and rock beneath the site of the Surface Facilities Area. A previously performed probabilistic seismic hazard analysis (PSHA) (CRWMS M&O 1998a [DIRS 103731]) estimated ground motions at a reference rock outcrop for the Yucca Mountain site (Point A), but those results do not include these site response effects. Thus, the additional step of applying the site-response ground motion model is required to develop ground motion inputs that are used for preclosure and postclosure purposes.The RVT-based equivalent-linear site response model involves a computational method (i.e., equivalent-linear) that has been widely employed to evaluate 1D site response using vertically propagating plane shear (S)-waves. Departures of soil response from a linear constitutive relation are treated in an approximate manner through the use of the equivalent-linear approach. Idriss and Seed (1968 [DIRS 163520]) introduced this approach, in its present form. Basically, the approach approximates a second-order nonlinear equation, over a limited range of its variables, by a linear equation. Formally this is done in such a way that the average of the difference between the two systems is minimized. This is done in an ad-hoc manner for ground response modeling by defining an effective strain that is taken to exist for the duration of the excitation. Shear modulus reduction and hysteretic damping curves are then used to define new parameters for each layer based on the effective strain computations. The linear response calculation is repeated, new effective strains evaluated, and iterations performed until the changes in parameters are belo...

Extreme ground motions and Yucca Mountain

“…Purvance and others (2009) also subjected these nine fragile structures to 16 ground-motion time histories created by Wong (2004) at Point B (the repository horizon; Stepp and others,2001) at 10 -5 /yr and 10 -6 /yr hazard levels for postclosure analysis of repository performance. Thirteen of the sixteen ground-motion time-histories at 10 -5 /yr overturned most or all of the nine PBRs.…”

USGS hazard map compatible depth-dependent seismic site coefficients for the Upper Mississippi Embayment

“…Toro and Silva (2001) andWong et al (2004) was used to generate 30 randomized shear wave velocity profiles for each site category. Following the recommendations ofRomero and Rix (2001), lognormal distribution of shear-wave velocity with s lnVs = 0.15 was assumed, and the correlation coefficient of the lognormal mean of adjacent layers was set to 0.5.…”

Soil-Column Depth-Dependent Seismic Site Coefficients and Hazard Maps for the Upper Mississippi Embayment

“…In order to consider the uncertainty in site response analysis due to variability in dynamic soil properties, two sets of randomized shear-wave velocity profiles representing the upland and lowland profiles are used in combination with two sets of normalized modulus reduction and damping curves as summarized in Table 6. The randomization methodology described in Toro and Silva (2001) and Wong et al (2004) is used to generate 30 randomized shear-wave velocity profiles for each of the upland or lowland profiles whose mean is shown in Figure 5 with the following constraints: 2. Correlation coefficient of the lognormal mean of adjacent layers is 0.5 (Romero and Rix, 2001); and 3.…”