- Ground-motion model is:
- Use two site classes that are consistent with Iranian design code and derive equations for each separately:
- V s < 375m∕s.
- V s > 375m∕s.
- Response parameter is acceleration for 5% damping.
- Focal depths between 5 and 59km but most 10km.
- Based on Amiri et al. (2007a) (see Section 2.268) but using larger and reappraised dataset.
- Derive models for Zagros and Alborz-Central Iran separately.
- Note the poor quality of some Iranian strong-motion data. Selected data based on accuracy of independent
- State that faulting mechanism is known for only a small proportion of data. Therefore, it is not considered.
- Use Ms because it is the most common scale for Iranian earthquakes.
- Most data from Ms < 6.5 and 5 < rhypo < 200km. Note lack of near-source data from Ms > 6.
- Because of small and moderate size of most earthquakes used and since causative faults are not known
for many earthquakes use rhypo, which compute using S-P method because of uncertainty in reported
- Data from SMA-1 (about 210 records on soil and 130 on rock) and SSA-2 (about 220 records on soil and
170 on rock).
- Bandpass filter records using cut-off frequencies chosen based on instrument type and data quality. Cut-offs
chosen by trial and error based on magnitude and distance of record and obtained velocity. Generally
cut-offs are: 0.15–0.20Hz and 30–33Hz for SSA-2 on rock, 0.15–0.25Hz and 20–23Hz for SMA-1 on rock,
0.07–0.20Hz and 30–33Hz for SSA-2 on soil and 0.15–0.20Hz and 20–23Hz for SMA-1 on soil.
- Choose functional form after many tests (not shown) and because it is simple but physically justified.
- Note that predictions show peaks and valleys since no smoothing applied.
- Report that residual analysis (not shown) shows predictions are unbiased w.r.t. magnitude, distance and