- Ground-motion model used is:
- Response parameter is pseudo-acceleration for 5% damping.
- Uses two site categories (no soil profiles were available for Cascadia region):
S = 0
- Rock: average V s assumed to be about 2000m∕s
S = 1
- Soil: average V s assumed to be about 255m∕s (although includes some soft soil sites with average V s
- Tectonic type of earthquakes used: crustal, subcrustal and subduction
- Most Cascadia data is from seismograms. Converts vertical measurements from these to one horizontal
- Supplements in large magnitude range (6.7 < Mw ≤ 8.2) with data from 9 subduction earthquakes in
Alaska, Mexico, Japan and Chile
- Most magnitudes below 5.3 and no data between 6.8 and 7.5.
- Focal depths between 1 and 60km
- Only uses events recorded at 3 or more stations. Improves ability of regression to distinguish between
magnitude and distance dependencies in data.
- Most low magnitude events were recorded on rock and most high magnitude events were on soil. Thus to
stabilize regression takes the coefficients cs from Boore et al. (1994a) and not derived from this data.
- Magnitude partitioning, in first step, into 0.5 unit intervals gave evidence for magnitude dependent
attenuation. Uses ca1 = 1 for 4.1 ≤ Mw ≤ 6.7 and ca1 = 0.5 (largest which yielded positive ca2) for
Mw ≥ 7.5. Thought to show breakdown of point source assumption.
- Demonstrates depth dependence in anelastic decay by performing regression in four 15km deep subsets
for range 4.1 ≤ Mw ≤ 6.7. ca3 and ca4 then finds by regression for each period. No depth dependence for
Mw ≥ 7.5 because of lack of different depths.
- Includes depth dependence in second step because gave better fit for short periods.
- Checks dependence on crustal, interface and intra-slab events; finds no dependence.