- Ground-motion model is:
where Y is in cm∕s2, c0 = 4.16, c1 = 0.69, c2 = -1.24, R0 = 6, c3 = 0.12 and σ = 0.70.
- Use three site categories:
S = 0
- NEHRP and UBC category B. 145 records.
S = 1
- NEHRP and UBC category C. 378 records.
S = 2
- NEHRP and UBC category D. 221 records.
- Selection criteria are: a) earthquake has Mw ≥ 4.5, b) PGA ≥ 0.05g and c) PGA < 0.05g but another
record from same earthquake has PGA ≥ 0.05g.
- Records mainly from normal faulting earthquakes.
- Exclude data recorded in buildings with four stories or higher.
- Automatically digitize records and process records homogenously, paying special attention to the filters
- Correlation between Mw and R in set of records used. For 4.5 ≤ Mw ≤ 5.0 records exist at R ≤ 40km
and for larger magnitudes records exist at intermediate and long distances. For Mw > 6.0 there is a lack
of records for R < 20km.
- Use a two step regression method. In first step use all records to find c1. In second step use records from
earthquakes with Mw ≥ 5.0 to find c0, c2 and c3.
- Adopt R0 = 6km because difficult to find R0 via regression due to its strong correlation with c2. This
corresponds to average focal depth of earthquakes used.
- Also try Ground-motion model: lnY = c′0+c′1Mw+c′2 ln(R2+h02)1∕2+c′3S. Coefficients are: c′0 = 3.52,
c′1 = 0.70, c′2 = -1.14, h0 = 7km (adopted), c′3 = 0.12 and σ = 0.70.
- Find no apparent trends in residuals w.r.t. distance.
- Due to distribution of data, equations valid for 5 ≤ R ≤ 120km and 4.5 ≤ Mw ≤ 7.0.