Ground Motion and Site Response in Las Vegas Seismic Ground Motion and Site Response in Las Vegas Valley, Nevada from NTS Explosions (original) (raw)
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Seismic Wave Amplification in Las Vegas: Site Response and Empirical Estimates of Ground Motion
2004
This presentation will summarize a multidisciplinary effort to understand seismic wave amplification in Las Vegas Valley. The project involves weak motion recording and analysis, geotechnical and seismic refraction field studies, geologic and lithologic interpretation and model building. We will provide a brief overview of the project, then focus on specifics of seismic wave amplification including observations and interpretations. We analyzed recordings of nuclear explosions from the Nevada Test Site (NTS) and regional earthquakes to estimate site response in Las Vegas. An empirical transfer function method was used to transform ground motion time-series at one (reference) station to other stations, using frequency dependent site response curves in the band 0.2-5.0 Hz. The method transforms the time-series to the frequency domain by Fast Fourier transform, multiplies the amplitude spectrum by the site response curve and inverse FFT's back to the time domain. The approach is va...
Seismic Wave Amplification in Las Vegas: Site Characterization Measurements and Response Models
2004
As part of a multidisciplinary effort to understand seismic wave amplification in Las Vegas Valley, we conducted geotechnical and seismic refraction field studies, geologic and lithologic interpretation, and geophysical model building. Frequency-dependent amplifications (site response) and peak ground motions strongly correlate with site conditions as characterized by the models. The models include basin depths and velocities, which also correlate against ground motions. Preliminary geologic models were constructed from detailed geologic and fault mapping, logs of over 500 wells penetrating greater than 200 m depth, gravity-inversion results from the USGS, and USDA soil maps. Valley-wide refraction studies we conducted in 2002 and 2003 were inverted for constraints on basin geometry, and deep basin and basement P velocities with some 3-d control to depths of 5 km. Surface-wave studies during 2002-2004 characterized more than 75 sites within the Valley for shear velocity to depths ex...
This paper reports on studies investigating source and propagation effects of seismic waves emitted by small chemical explosions conducted in the granites of Climax Stock on the Nevada National Security Site (formerly the Nevada Test Site) as part of the Source Physics Experiments (SPE). To date, two such explosions (SPE-1 and SPE-2) have been executed with chemical yields of 100 and 1000 kg and burial depths of 55 and 46 m, respectively. A third experiment conducted in the summer of 2012 is not reported on in this paper. As many as four follow-on experiments in this SPE series are planned in subsequent years. All experiments are designed to be detonated in the same emplacement hole and recorded by the same free-field, free-surface, close-in, and local networks of ground- motion sensors, including some infrasound sensors. The focus of this paper is on the analysis and modeling of waveforms recorded close-in on five linear geophone lines emanating on a spread of azimuths from ground ...
First-generation site-response maps for the Los Angeles region based on earthquake ground motions
Bulletin of the Seismological Society of America
Ground-motion records from aftershocks of the 1994 Northridge earthquake and mainshock records from the 1971 San Fernando, 1987 Whittier Narrows, 1991 Sierra Madre, and 1994 Northridge earthquakes are used to estimate site response relative to a rock site for the urban Los Angeles area. Site response is estimated at 232 mainshock and 201 aftershock sites relative to a low-amplitude site in the Santa Monica Mountains. Average amplification values are calculated for the frequency bands: 1 to 3, 3 to 5, and 5 to 7 Hz. These bands are chosen based on limitations in aftershock recording equipment at lower frequencies and reduced significance to the building inventory at higher frequencies. Site amplification factors determined at the instrumented locations are grouped by the surficial geology and contoured to produce a continuous spatial estimation of amplification. The maps in this article represent the first attempt to produce estimates of site amplification based on observations of gr...