- Ground-motion model is:
_{1}= -0.2, c_{2}= 0.59, c_{3}= -0.0039, c_{4}= 1, c_{5}= 0.008, σ_{r}= 0.27, σ_{e}= 0.10 and for vertical PGA: c_{1}= -0.4, c_{2}= 0.60, c_{3}= -0.0036, c_{4}= 1, c_{5}= 0.006, σ_{r}= 0.25 and σ_{e}= 0.11 where σ_{r}is the intra-event standard deviation and σ_{e}is the inter-event standard deviation. - All data from 51 hard (NEHRP B) sites.
- All stations in the Valley of Mexico omitted.
- All data from free-field stations: small shelters, isolated from any building, dam abutment, bridge, or structure with more than one storey.
- Focal depths: 35 ≤ H ≤ 138km, most records (13 earthquakes, 249 records) from 35 ≤ H ≤ 75km.
- Exclude data from M
_{w}< 5.0 and R > 400km. - Exclude data from deep earthquakes where wave paths cross the mantle edge.
- All data from normal-faulting earthquakes.
- Use about 27 records from velocity records from broadband seismograph network that were differentiated to acceleration.
- Adopt Δ from Atkinson and Boore (2003).
- Investigate a number of functional forms. Inclusion of Δ substantially improves fit, leading to a decrease
in random variability at close distances, and an increase in c
_{2}and c_{3}coefficients. Find worse correlation when add a quadratic magnitude term. A magnitude-dependent c_{4}leads to higher σs. Find unrealistically high ground motions at close distances using the form of c_{4}used by Atkinson and Boore (2003). - If exclude three deep earthquakes then little dependence on H.
- Do not find any noticeable bias in residuals w.r.t. distance, magnitude or depth (not shown).
- Note that decrease in variability w.r.t. magnitude is only apparent for frequencies < 1Hz.
- Discuss observed dependence of, particularly high-frequency, ground motions on focal depth.