Spectral Characteristics of Small Magnitude Earthquakes with Application to Western and Eastern North American Tectonic Environments: Surface Motions and Depth Effects.

摘要

The band-limited-white-noise model employed in the WES-RASCAL computer program was used to predict response spectral shapes for smallmagnitude earthquakes (moment magnitude (m sub w)=approx. 5.3 to 2.5) in both eastern and western North America. Model predictions are compared to spectral shapes computed from seismic data recorded in both eastern North America (ENA) and western North America (WNA) tectonic provinces. The ground motion model produces reliable and accurate predictions of spectral composition as well as peak accelerations for these small magnitude earthquakes. Results of magnitude and distance scaling of response spectral shapes show little distance dependence in the range of 5 to 25 km, but a strong magnitude dependence in the range m sub w 2.5 to 5.3. Representative synthetic acceleration time histories were also generated at close ranges for rock outcrops with properties typical of WNA and ENA. The synthetic motions compare favorably in peak acceleration, duration, and spectral content with recorded data at comparable magnitudes and ranges. Ground motions are also examined at depths of 50, 100 and 150 m within a half space. Effects of depth upon response spectra, Fourier spectra, peak acceleration, and peak particle velocity are shown. Depth-dependent spectral nodes are present in the Fourier and response spectra. Both peak acceleration and peak particle velocity decrease with depth. Peak acceleration decreases more rapidly with depth than does peak particle velocity. Keywords: Earthquakes ground motion; Response spectra; Computer programs; Tectonics mathematical prediction; Seismic magnitude. (EDC)