- Ground-motion model is (model 1):
where A is in cm∕s2, a = 2.11, b = 1.23 and d = -0.014.
Ground-motion model is (model 2): where A is in m∕s2, c1 and c2 are from Dahle et al. (1990b), c4 = -0.0148 and σ is recommended as 0.65
(although this is from an earlier study and is not calculated in regression).
- Use data from Canada (Saguenay earthquake and Nahanni sequence) and Belgium (Roermond earthquake).
- Focal depths, h, between 1 and 30km with average 14.4km.
- Assume peak ground acceleration equals pseudo-acceleration at 30Hz due to few unclipped horizontal UK
records and because instrument response of UK instruments means records unreliable above 30Hz. Use
only digital VME records for 30Hz model.
- Note poorness of data due to UK data and other data being widely separated thus preventing a comparison
between the two sets. Also means straightforward regression methods would be inadequate as there would
be little control on shape of curves derived.
- Note earlier models over predict UK data.
- Use two-stage least squares method to give model 1. First stage fit only UK/Belgian data to find b, in
second stage use this value of b and use all data to find a and d.
- Do not recommend model 1 for general use because too influenced by limitations of data to be considered
reliable. Canadian data probably insufficient to anchor curves at small R/large M and extremely high
Saguenay earthquake records carry undue weight.
- Use model of Dahle et al. (1990b) to get model 2. Fix c1 and c2 to those of Dahle et al. (1990b) and find
c4. Prefer this model.