- Ground-motion model is:
- Response parameter is acceleration for 2 and 5% damping.
- Use three site categories (GC) for which perform separate regression:
- Ground characteristic index ≲ 0.67, 29 records.
- Ground characteristic index between about 0.67 and 1.50, 46 records.
- Ground characteristic index ≳ 1.50, 22 records.
where the ground characteristic index is calculated from statistical analysis of amplitude of records.
Thought to reflect the characteristic of deep soil deposits at site (1.0 means amplification is average for
Japan, < 1.0 or > 1.0 means amplification is lower or greater, respectively, than average for Japan).
- Records from JMA low-magnification mechanical seismographs (natural period 6s, damping ratio 0.55)
which were instrument corrected (because sensitivity for periods > 10s is substantially suppressed) , filtered
(cut-offs 1.3–2s and 20–30s chosen from a study of recording accuracy of instruments) and differentiated
in frequency domain to find ground velocity and acceleration. Hence limit analysis to 2 to 20s.
- Do not use resultant of two horizontal components because two components not synchronous.
- Find difference in predicted ground motion using derived equations and those from earlier equations for
short periods. Find that b for earlier equations increases almost linearly with logarithm of natural period,
T, so find equation, by least squares, connecting b and log T. Assume this equation holds for 2 to 20s and
so fix b and recalculate a and c; find predictions now agree.
- Only give graphs for original coefficients for 5% damping. Give tables of coefficients for preferred second