- Ground-motion model is:
where Y is in g, C

_{1}= 0.040311, C_{2}= 0.417342, C_{3}= 0.001, C_{4}= 0.65, C_{5}= -0.351119 and C_{6}= -0.035852 for horizontal PGA and C_{1}= 0.0015, C_{2}= 0.8548, C_{3}= 0.001, C_{4}= 0.4, C_{5}= -0.463 and C_{6}= 0.0006 for vertical PGA. - Uses two site categories:
- S = 0
- Rock, site categories I and II of Iranian building code.
- S = 1
- Soil, site categories III and IV of Iranian building code.

- Selection criteria are: i) causative earthquake, earthquake fault (if known) and respective parameters are determined with reasonable accuracy, ii) PGA of at least one component > 50gal, iii) records from free-field conditions or ground level of low-rise buildings (< three stories), iv) some aftershocks have been eliminated to control effect of a few large earthquakes and v) records have been processed with acceptable filter parameters.
- Regresses directly on Y not on logarithm of Y . Therefore does not calculate standard deviation in normal
way. Considers the deviation of individual records from predictive equations as being PGA dependent.
Finds that a sigmoidal model fits the data well. Therefore Y = (ab + cx
^{d})∕(b + x^{d}) where Y is the error term and x is the predicted ground motion, a = 0.038723, b = 0.00207, c = 0.29094 and d = 4.97132 for horizontal PGA and a = 0.00561, b = 0.0164, c = 0.1648 and d = 1.9524 for vertical PGA.