- Ground-motion model is: where Y is in cm∕s2, for horizontal PGA: c1 = -0.2, c2 = 0.59, c3 = -0.0039, c4 = 1, c5 = 0.008,
σr = 0.27, σe = 0.10 and for vertical PGA: c1 = -0.4, c2 = 0.60, c3 = -0.0036, c4 = 1, c5 = 0.006,
σr = 0.25 and σe = 0.11 where σr is the intra-event standard deviation and σe is the inter-event standard
- 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 Mw < 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
- 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 c2 and c3 coefficients. Find worse correlation
when add a quadratic magnitude term. A magnitude-dependent c4 leads to higher σs. Find unrealistically
high ground motions at close distances using the form of c4 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.