- Ground-motion model (Model 1) is:
where PGA is in m∕s2, δR = 1 for crustal reverse 0 otherwise, δA = 1 for rock 0 otherwise, δI = 1 for
interface 0 otherwise, A1 = 0.298, A2 = -1.56, A3 = 0.00619, A4 = -0.365, A5 = 0.107, A6 = -0.186,
A7 = -0.124, d = 19 and σ = 0.230.
- Models also given for soil sites only (Model 2), unspecified site (Model 3), focal mechanism and tectonic
type unknown (Model 4) and only magnitude, depth and distance known (Model 5)
- Records from ground or base of buildings. 33 from buildings with more than 3 storeys; find no significant
- Retain two site categories:
- Rock: Topographic effects expected, very thin soil layer (≤ 3m) overlying rock or rock outcrop.
- Soil: everything else
- Use depth to centroid of rupture, hc, 4 ≤ hc ≤ 149. Only nine are deeper than 50km. Exclude records from
deep events which travelled through mantle.
- Consider tectonic type: C=crustal (24+17 records), I=interface (7+0 records) and S=slab (20+0 records)
- Consider source mechanism: N=normal (15+1 records), R=reverse (22+5 records) and S=strike-slip
(12+11 records). Classify mixed mechanisms by ratio of components ≥ 1.0.
- For only five records difference between the distance to rupture surface and the distance to centroid could
be more than 10%.
- 66 foreign near-source records (dr ≤ 10km) from 17 crustal earthquakes supplement NZ data. Mainly from
western North America including 17 from Imperial Valley and 12 from Northridge.
- Exclude one station’s records (Atene A) due to possible topographical effects.
- Exclude records which could have been affected by different attenuation properties in the volcanic region.
- Note regional difference between Fiordland and volcanic region and rest of country but do model.
- Retain coefficients if significant at α = 0.05.
- Anelastic term not significant.