- Ground-motion model is:
where pga is in g, c1 = -3.27, c3 = -1.79 and σtotal = 0.46 for deep soil and c1 = -3.56, c3 = -1.67 and
σtotal = 0.46 for rock/shallow soil.
- Originally use five site classes (chosen based on site response analyses using broad categories and generic site
- Rock. 66 records
- Shallow soil (< 250ft. 6 records.)
- Intermediate depth soil (250–1000ft). 2 records.
- Deep soil (> 1000ft). 51 records.
- Alluvium of unknown depth. 10 records.
but insufficient records in shallow and intermediate classes to evaluate separately so combine rock and
shallow classes and intermediate, deep and unknown depth categories to leave two classes: < 250ft and
- Use two faulting mechanisms:
F = 0
F = 1
- Reverse or oblique
- Process data by: 1) interpolation of uncorrected unevenly sampled records to 400 samples per second;
2) frequency domain low-pass filtering using a causal five-pole Butterworth filter with corner frequencies
selected based on visual examination of Fourier amplitude spectrum; 3) removal of instrument response;
4) decimation to 100 or 200 samples per second depending on low-pass filter corner frequencies; and 5)
application of time-domain baseline correction, using polynomials of degrees zero to ten depending on
integrated displacements, and final high-pass filter chosen based on integrated displacements that is flat at
corner frequency and falls off proportional to frequency on either side, which is applied in the time domain
twice (forward and backwards) to result in zero phase shift.
- Note that due to limited magnitude range of data, magnitude dependence is not well constrained nor is
dependency on mechanism. Hence these coefficients are fixed based on previous studies.
- Plot residuals w.r.t. distance. Find slight increase at 70–100km. To test if due to Moho bounce repeat
regression assuming functional form that is flat between 70 and 90km but this produced a smaller likelihood.
Conclude that data does not support significant flattening at < 100km.
- Note that model is preliminary.