- Ground-motion model is:
- Consider two site classifications (without regard to depths of deposits) but do not model:
- 1.
- Rock
- 2.
- Alluvium

- Select records which have: M
_{s}≥ 4.0 and standard deviation of M_{s}known and reliable estimates of source-site distance and focal depth, h ≤ 25km, regardless of local soil conditions from free-field and bases of small buildings. No reliable data or outliers excluded. Records from instruments at further distances from the source than the closest non-triggered instrument were non-excluded because of non-homogeneous and irregularly spaced networks and different and unknown trigger levels. - Most data, about 70%, with distances less than 40km. Note strong bias towards smaller values of magnitude and PGA.
- PGA read from analogue and digitised data, with different levels of processing. Differences due to different processing usually below 5%, but some may be larger.
- Errors in distances for small shocks may be large.
- Prefer one-stage technique because second step of two-stage method would ignore records from
singly-recorded earthquakes which compose over half the events, also find more realistic, b, and h
_{0}using one-stage method. Do not use weighting because involves assumptions which are difficult to verify. - Find inadmissable and positive b for vertical PGA so remove and repeat.
- Remove records from distances less than or equal to half their focal depth and also less than or equal to
their focal depth, find that h
_{0}is governed by near-field data. - Use focal depth explicitly, by replacing r = (d
^{2}+h_{0}^{2})^{1∕2}by r = (d^{2}+h^{2})^{1∕2}. Find lower standard deviation and that it is very significant. - Repeat analysis on subsets of records grouped by focal depth. Find no correlation between h
_{0}and focal depth of subset. Use h_{0}equal to mean focal depth in each subset and find similar results to when focal depth used explicitly. - Repeat analysis with geometric attenuation coefficient equal to -0.83, corresponding to the Airy phase, as opposed to -1.0.
- Find small dependence of horizontal PGA on site classification, note due to level of information available.