- Ground-motion model is:
where A is in gal, a = 0.38, b = 0.0045, d = 0.005, c1 = 1.30, c2 = 1.35, c3 = 1.53, f = 0.03, g = 0.02,
σintra = 0.23, σinter = 0.16 and σtotal = 0.28.
- Use 3 site classes (same as Iranian Code of Practice for the Seismic Resistant Design of Buildings):
- V s,30 > 750m∕s. Average V s,30 = 994m∕s. 135 records. c1 = 1 and c2 = c3 = 0.
- 375 ≤ V s,30 ≤ 750m∕s. Average V s,30 = 558m∕s. 160 records. c2 = 1 and c1 = c3 = 0.
- 175 ≤ V s,30 ≤ 375m∕s. Average V s,30 = 306m∕s. 56 records. c3 = 1 and c1 = c2 = 0.
There is a fourth class in the Iranian code (V s,30 < 175m∕s) but no records from this class so not considered
- Consider two faulting mechanisms:
- F = 0
- F = 1
Exclude data from normal-faulting events, which occur rarely in Iran.
- Use data from free-field or ground floors from stations of the Iran Strong Motion Network of the Building
and Housing Research Centre from 07/03/1975 to 07/12/2008. Data from SSA-2 (digital) and SMA-1
- Select data using these criteria: Mw ≥ 5.0, records from ground surface and both horizontal components
available. Apply Mw-dependent truncation of distant records because instrument acceleration trigger is
- Consider difference in motions between Central Iran (42 events, Z = 0) and Zagros (36 events, Z = 1)
zones, where tectonics are different.
- Focal depths between 5 and 34km. Exclude deeper events because insufficient data.
- Filter records with bandpass cosine filter with cut-offs 0.2 and 20Hz, which were chosen based on
characteristics of instruments.
- Exclude data from events with specific geological or other effects.
- 83% of data have PGA< 100gal hence do not consider nonlinear site response.
- Majority of data from Mw ≤ 6.5.
- Examine residuals w.r.t. Mw, r, focal depth, zone and faulting mechanism and find no significant trends.
Based on these plots believe model reliable for 5.0 ≤ Mw ≤ 7.3 in Central Iran and 5.0 ≤ Mw ≤ 6.5 in
Zagros, 15 ≤ rrup ≤ 135km and focal depths 7–27km.
- Believe higher motions in Zagros zone due to ductile bed, which means ruptures do not reach surface.