- Ground-motion model is:
where PGA is in gal, using all PGA values p1 = 6.36, p2 = 1.76, p4 = -2.73, p5 = 1.58, p6 = 0.608,
p7 = 0.00916 and σ = 0.773.
- Use data from stiff soil sites (depth of soil < 25m).
- Include data from any zones with strong seismic coupling, such as the younger subduction zones (S.W.
Japan, Alaska, C. America (Mexico), C. Chile, Peru and northern Honshu and Kuril subduction zones
in Japan) unless compelling reasons to exclude data. Do this because lack of data from Cascadia. Most
(> 70%) are from Japan.
- Focal depths, h, between 0 and 238km.
- Compare Japanese and Cascadia PGA values for earthquakes with similar magnitude and depths and find
- Do not exclude data from buildings or which triggered on S-wave. Note could mean some PGAs are
- Plot ground motion amplitude (PGA and also some maximum displacements from seismograms) against
distance for a number of large magnitude shocks (including some data from rock sites which not included
in set for regression). Find that rate of attenuation becomes smaller for shorter distances and process is
magnitude dependent. Also plot Japanese PGA data, from earthquakes with h ≤ 50km, split into three
distance groups (between 50 and 75km, between 100 and 150km and between 250 and 300km) find as
distance increases magnitude scaling becomes larger and possible saturation in PGA for large magnitudes.
Fit lnPGA = p1 + p2 ln(R + C) to some PGA values from large magnitude shocks for C = 0 and C > 0,
find lower standard deviation for C > 0.
- Fit lnPGA = a + bM and lnPGA = a + bM + cM2 to Japanese data split into the three distance groups
(mentioned above); find b increases with increasing distance range but both equations fit data equally well.
- Constrain p4 to negative value and p5 and p6 to positive values.
- Include quadratic magnitude term, p3M2, but find equal to zero.
- Plot residuals against M; find uniformly distributed and evidence for smaller residuals for larger M.
- Plot residuals against R
and find decreasing residuals for increasing R.
- Give equation using only those records available in digital form (235 records).