where is expected peak acceleration on rock as predicted by the attenuation equation with S = 0.
Response parameter is acceleration for unspecified5
damping.
Use two site categories:
S = 0
Rock: rock (Vs> 600m∕s), very thin soil (< 5m) over rock or soil 5 to 20m thick over rock.
S = 1
Deep soil: deep soil in narrow canyon (soil > 20m thick and canyon < 2km wide) or deep soil in broad
canyon (soil > 20m thick and canyon > 2km wide).
All records reprocessed using common procedure. Interpolated to 400 samples/sec, low-pass filtering with
corner frequency selected for each record based on visual examination of Fourier amplitude spectrum,
instrument corrected, decimated to 100 to 200 samples/sec depending on low-pass corner frequency,
baseline correction using 0 to 10 degree polynomial, high-pass filtered based on integrated displacements.
Only use response spectral data within frequency band 1.25fh to 0.8fl to avoid effects of filter roll-off.
Hence number of records used for regression at each period varies, minimum number is less than 100
records for 0.01s.
Well distributed dataset in terms of magnitude and distance.
Supplement data with records from Gazli, Friuli, Tabas, Taiwan, Nahanni and Spitak.
Consider source mechanism: reverse ⇒ F = 1, reverse/oblique ⇒ F = 0.5, others (strike-slip and normal)
⇒ F = 0).
Consider hanging wall effect: if over hanging wall HW= 1, otherwise HW= 0.
Note that interpretation of c4 is not clear for their distance measure but yields better fit.
Model nonlinear soil response by f5.
Model uncertainty as magnitude dependent.
Fix some coefficients to be independent of period so that response spectral values vary smoothly with
distance, magnitude and period.
Smooth coefficients using piecewise continuous linear fits on log period axis. For highly correlated
coefficients, smooth one coefficient and re-estimate other coefficients.
4f3given in Abrahamson and Silva (1997) was modified to ensure homogeneity and a linear variation in f3with magnitude.