- Ground-motion model is:
- Most data from shallow stiff soil and sedimentary deposits between about 5 and 25m deep on Tertiary or
- Response parameter is pseudo-velocity for 5% damping.
- All earthquakes from Benioff-Wadati zones.
- Exclude data with magnitudes or distances well outside range of most selected records.
- Focal depths, h between 14 and 130km.
- No strong correlations between h, R and M.
- Try terms eM2 and fR but find not significant (using t-test).
- Try term R + C1 exp(C2M) instead of R; find similar standard errors.
- Find d is insignificant for 0.6 to 2s; find d does not significantly reduce standard errors.
- Find residuals are normally distributed (by plotting on normal probability paper and by
- Split data by fault mechanism (thrust: 49 records, normal: 11 records, strike-slip: 4 records) and find
attenuation equation for each subset; results are not significantly different (at 95% using F test). Also
check by examining normal deviates (normalised residuals) for each subset and period; find no significant
- Use 131 records from six other subduction zones (Nankai, Kuril, Alaska, Peru/N. Chile, Mexico and New
Britain/Bougainville) to examine whether ground motions from all subduction zones are similar.
- Examine normal deviates for residuals between other zones’ ground motion and N. Honshu equation.
Find no significant differences (although obtain significant results for some periods and focal mechanisms)
between N. Honshu, Kuril and Nankai motions. Find differences for Alaskan and Mexican data but could
be due to site effects (because some data from soft soil sites). Find differences for Peru/N. Chile and New
Britain/Bougainville which are probably source effects.
- Plot seismotectonic data (age, convergence rate, dip, contact width, maximum subduction depth, maximum
historical earthquake (Mw), maximum rupture length, stress drop and seismic slip) against decreasing
ground motion at stiff sites for T > 0.8s. Find weak correlations for stress drop and Mw (if ignore Mexican
data) but due to variability in stress drop estimates note lack of confidence in results.