- Ground-motion model is:
where units of A not given (but probably m∕s2), for vertical PGA a = 0.362, b = 0.0002, c1 = -1.124,
c2 = -1.150, c3 = -1.139, c4 = -1.064, d = 1 and σ = 0.336 and for horizontal PGA a = 0.360,
b = 0.0003, c1 = -0.916, c2 = -0.862, c3 = -0.900, c4 = -0.859, d = 1 and σ = 0.333.
- Use four site categories, which were based on H∕V receiver function (RF) measurements (use geotechnical
measurements at 50 sites and strong-motion accelerograms at other sites):
Site class 1
- RF does not exhibit any significant amplification below 15Hz. Corresponds to rock and stiff sediment
sites with average S-wave velocity in top 30m (V s,30) > 700m∕s. Use c1.
Site class 2
- RF exhibits a fundamental peak exceeding 3 at a frequency between 5 and 15Hz. Corresponds to stiff
sediments and/or soft rocks with 500 < V s,30 ≤ 700m∕s. Use c2.
Site class 3
- RF exhibits peaks between 2 and 5Hz. Corresponds to alluvial sites with 300 < V s,30 ≤ 500m∕s. Use
Site class 4
- RF exhibits peaks for frequencies < 2Hz. Corresponds to thick soft alluvium. Use c4.
- Only 100 records are associated with earthquakes with known focal mechanisms, 40 correspond to
strike-slip/reverse, 31 to pure strike-slip, 24 to pure reverse and 4 to a pure vertical plane. Note that use
of equations should be limited to sources with such mechanisms.
- Use only records for which the signal to noise ratio was acceptable.
- Source parameters from teleseismic studies available for 279 records.
- Calculate source parameters directly from the strong-motion records for the remaining 189 digital records
using a source model. Hypocentral distance from S-P time and seismic moment from level of acceleration
spectra plateau and corner frequency.
- Focal depths from 9 to 133km but focal depth determination is very imprecise and majority of earthquakes
- Suggest that whenever estimation of depth of earthquake is impossible use distance to surface projection
of fault rather than hypocentral distance because differences between hypocentral and epicentral distances
are not significant for shallow earthquakes.
- Also derive equations based only on data from the Zagros thrust fault zone (higher seismic activity rate
with many earthquakes with 4 ≤ M ≤ 6) and based only on data from the Alborz-Central Iran zone (lower
seismic activity rate but higher magnitude earthquakes). Find some differences between regions.
- Investigate fixing d to 1 (corresponding to body waves) and to 0.5 (corresponding to surface waves).
- Note that there are very few (only two) near-field (from less than 10km from surface fault rupture) records
from earthquakes with Mw > 6.0 and so results are less certain for such combinations of magnitude and