Behavior of Peak Vertical Acceleration Across Small Two- Dimensional Strong-Motion Array

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This is a 1985 SBIR Phase II award. Spatial coherence of the vertical component of ground motion across a dense two-dimen- sional array for as many as 30 shallow earthquakes which produced approximately 200 high quality observations over a small area of engineering interest at distance of 50 km or less will be studied. The data consists of digitally recorded vertical accelerograms, across the 12-element inner-ing subarray (200m radius) of the SMART-1 Array in northeastern Taiwan, plus the central station. The abundant near-source strong ground motion data permit major improvements in the attenuation relation and the shape of vertical response spectra, both of critical impor- tance in engineering design, and their associated uncertainties. For the projected subarray the uncertainties are only minimally affected by site classification. Dispersion of the ground motion parameters in time and frequency domains will be studied as a function of source depth, distance, azimuth and magnitude. The impact of known subsurface structure and the anelastic response of the soil column (for different levels of shaking) will be evaluated. Understanding of the near-source behavior of vertical acceleration across a dense array outside the western U.S. allows independent verification f assumed relationship between vertical and horizontal ground motion parameters and devise of new site specific attenuation law and response spectra both of engineering importance in the design.