- Ground-motion model is:
_{0}= 2.7 and σ = 0.24, for vertical PGA not including focal depth A = -1.72, B = 0.243, C = -0.00174, D = -0.750, h_{0}= 1.9 and σ = 0.24, for horizontal PGA including focal depth A = -1.06, B = 0.245, C = -0.00045, D = -1.016, h_{0}= h and σ = 0.25 and for vertical PGA including focal depth A = -1.33, B = 0.248, C = -0.00110, D = -1.000, h_{0}= h and σ = 0.25. - Reviews and re-evaluates distances, focal depths, magnitudes and PGAs because data from variety of
sources with different accuracy and reliability. For M
_{s}> 6.0 distances have acceptable accuracy but for M_{s}< 6.0 distance, depths and magnitudes are poorly known. Errors in locations for M_{s}< 6.0 still large with no foreseeable means of improving them. Use of r_{epi}for M_{s}< 6.0 justified because difference between r_{jb}and r_{epi}for small earthquakes is not larger than uncertainty in epicentre. Check and redetermine station locations; find large differences in excess of 15km for some stations. - Focal depths poorly determined. Revises 180 depths using S-start times (time between P and S-wave arrival).
- Focal depths h < 26km; most (60%+) between 4 and 14km.
- Does not use M
_{L}because no M_{L}values for Algeria, Iran, Pakistan, Turkey and former USSR and unreliable for other regions. Does not use magnitude calculated from strong-motion records because magnitude calculation requires point source approximation to be valid. Conversion from M_{L}to M_{s}should not be done because of uncertainty in conversion which should be retained. - Notes that M
_{s}results in nonlinear scaling on PGA with M_{w}due to nonlinear relationship between log M_{0}and M_{s}. - Uses PGAs in four forms: maximum values from accelerograms read by others (34%), from corrected records (30%), scaled directly from accelerograms (13%) and from digitised plots (23%). Notes potential bias in using both corrected and uncorrected PGAs but neglects it because small difference (≲ 4% for those checked). Excludes PGAs near trigger level because processing errors can be large. Some unfiltered digital records which require additional processing to simulate SMA-1 could be associated with larger differences (≲ 10%).
- Excludes records from basements and ground floors of structures with more than 3 levels. Retains the few records from dam abutments and tunnel portals.
- Excludes records generated by close small magnitude earthquakes triggered by S-wave.
- Does not exclude records obtained at distances greater than shortest distance to an operational but not triggered instrument because of non-constant or unknown trigger levels and possible malfunctions of instruments.
- Uses weighted regression of Joyner and Boore (1988) for second stage.
- Splits data into five magnitude dependent subsets: 2.0 ≤ M
_{s}≤ 7.3 (1260 records from 619 shocks), 3.0 ≤ M_{s}≤ 7.3 (1189 records from 561 shocks), 4.0 ≤ M_{s}≤ 7.3 (830 records from 334 shocks), , 5.0 ≤ M_{s}≤ 7.3 (434 records from 107 shocks), and 3.0 ≤ M_{s}≤ 6.0 (976 records from 524 shocks). Calculates coefficients for each subset. Finds only small differences ±15% over distance range 1–200km between predictions and uncertainties. Concludes results stable. Prefers results from subset with 4.0 ≤ M_{s}≤ 7.3. - Finds it difficult to obtain some vertical accelerations due to low ground motion so ignores data from > 100km with PGA < 1%g (0.1m∕s2).
- Repeats regression using r
^{2}= d^{2}+ h^{2}. Finds depth important. - Calculates using one-stage method; finds very similar results for 10 < d < 100km.
- Considers magnitude dependent function: log a = b
_{1}+ b_{2}M_{s}+ b_{3}r + b_{4}[r + b_{5}exp(b_{6}M_{s})]. Finds b_{5}is zero so drops b_{3}and repeats. Finds b_{5}close to zero so magnitude dependent function not valid for this dataset. - Local shear-wave velocity, V
_{s}, profiles known for 44 stations (268 records from 132 earthquakes between 2.5 and 7.2) although only 14 from > 40km so barely sufficient to derive equation. Use 145 records from 50 earthquakes with M_{s}> 4.0 to fit log a = A + BM_{s}+ Cr + D log r + E log V_{s30}, where V_{s30}is average shear-wave velocity to reference depth of 30m. Finds C positive so constrain to zero. Find no reduction in standard deviation. - Uses residuals from main equation to find E. Notes that should not be used because of small number
of records. Considers different choices of reference depth; finds using between 5 and 10m leads to higher
predicted amplifications. Notes better to use V
_{s30}because no need for subjective selection of categories.