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Geophysical Techniques For Characterizing Shallow Velocity-Attenuation Models
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 5th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 1992, cp-210-00025
Abstract
Knowledge of seismic shear wave velocity and Q is required for both seismic<br>hazard analysis and the siting of critical structures since these parameters govern<br>the transmission of the seismic signal from the earthquake to the site and also<br>control the site response itself. These parameters vary spatially and may not be<br>readily available. The purpose of this paper is to show how these can be<br>estimated using surface-wave analysis techniques.<br>Data from USGS refraction surveys in Maine were selected which show dispersed<br>short-period Rg waves (fundamental mode Rayleigh waves). Processing techniques<br>applied to the data include filtering, waveform inversion of selected trace,<br>phase velocity stacking, interactive amplitude processing, inversion of dispersion<br>parameters for a layered shear-wave velocity and Q model, and finally verifying<br>the derived velocity-attenuation models by comparing both shape, absoluteamplitude<br>and arrival times of synthetic and observed time series. The resultant<br>velocity models show that the shear-wave velocity varies between 2.43-2.81<br>km/set for surface layer and Qp is less than 50 in the upper kilometer of the<br>metamorphic terrain of Maine. The models correlate with the type of geologic<br>rocks encountered. While the study focused on upper crustal structure, the techniques<br>and experimental procedure can be used for shallow site characterization<br>by appropriate scaling of the data acquisition.