This report addresses observed ground motions at the site of the proposed surface facilities associated with the designated repository for high-level nuclear waste at Yucca Mountain, Nevada. In 2003 an accelerometer array was installed at three boreholes on the pad of the north portal of the ESF (Exploratory Studies Facility) at Yucca Mountain, Nevada, by the Nevada Seismological Laboratory (NSL). These boreholes, roughly 150 m apart and initially used for extensive geological and geophysical surveys, were ideal locations to measure the subsurface ground motions at the proposed site of surface facilities such as the Waste Handling Building. Such measurements will impact the design of the facilities. Accelerometer emplacement depths of approximately 15 m from the surface and then at the bottom of the boreholes, roughly 100 m, were chosen. Accelerometers were also placed at the surface next to the boreholes, for a total of nine accelerometers, all three-component. Data recording was accomplished with onsite recorders, with the onsite data transmitted to a central computer at a trailer on the pad. All requirements were met to qualify these data as “Q”. Due to the lack of significant recordings during 2003, several low signal-to-noise (S/N) quality events were chosen for processing. The maximum horizontal peak ground acceleration (PGA) recorded at the pad was approximately 1 cm/s2 in 2003;the corresponding peak ground velocity (PGV) was approximately 0.01 cm/s. PGA and PGV were obtained at all nine accelerometers for most of these events, and spectra were computed. Ground motion amplitudes varied significantly across the boreholes. Higher ground amplifications were observed at the surface for the two boreholes that penetrated a thick amount (~ 30 m) of fill and Quaternary alluvium compared to the one that had less than 2 m of such. Additionally, surface-to-deep recordings showed as much as a factor of five amplification at these two boreholes. Signal correlation with inter-borehole distance agrees with basic Initial Borehole Accelerometer Array Observations Near the North Portal of the ESF Page 6 of 87 scattering theory, and the recorded signals across the wavefront correlate more strongly than those along the propagation path. Transfer functions computed from layered models for each borehole reflect some of the actual signal attributes fairly well, but many more signals need to be recorded and used to provide a good basis of comparison.
Earthquake hazard analysis; Earthquake magnitude -- Measurement; Nevada – Yucca Mountain
Earth Sciences | Geophysics and Seismology
Seggern, D. v.,
Brune, J. N.,
Smiecinski, A. J.
Initial borehole accelerometer array observations near the north portal of the ESF.
Available at: http://digitalscholarship.unlv.edu/yucca_mtn_pubs/65