- Ground-motion model is: where a is in g, for 4.0 ≤ M ≤ 7.4: for horizontal PGA not including focal depth A = -1.43, B = 0.245,
C = -0.0010, D = -0.786, h0 = 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, h0 = 1.9 and σ = 0.24, for horizontal PGA including focal depth
A = -1.06, B = 0.245, C = -0.00045, D = -1.016, h0 = h and σ = 0.25 and for vertical PGA including
focal depth A = -1.33, B = 0.248, C = -0.00110, D = -1.000, h0 = 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 Ms > 6.0 distances have acceptable accuracy but for
Ms < 6.0 distance, depths and magnitudes are poorly known. Errors in locations for Ms < 6.0 still large
with no foreseeable means of improving them. Use of repi for Ms < 6.0 justified because difference between
rjb and repi 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
- Focal depths h < 26km; most (60%+) between 4 and 14km.
- Does not use ML because no ML 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 ML to Ms should not be
done because of uncertainty in conversion which should be retained.
- Notes that Ms results in nonlinear scaling on PGA with Mw due to nonlinear relationship between log M0
- 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
- 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
- Uses weighted regression of Joyner and Boore (1988) for second stage.
- Splits data into five magnitude dependent subsets: 2.0 ≤ Ms ≤ 7.3 (1260 records from 619 shocks),
3.0 ≤ Ms ≤ 7.3 (1189 records from 561 shocks), 4.0 ≤ Ms ≤ 7.3 (830 records from 334 shocks),
, 5.0 ≤ Ms ≤ 7.3 (434 records from 107 shocks), and 3.0 ≤ Ms ≤ 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 ≤ Ms ≤ 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 r2 = d2 + h2. Finds depth important.
- Calculates using one-stage method; finds very similar results for 10 < d < 100km.
- Considers magnitude dependent function: log a = b1 + b2Ms + b3r + b4[r + b5 exp(b6Ms)]. Finds b5 is zero
so drops b3 and repeats. Finds b5 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 Ms > 4.0 to fit log a = A + BMs + 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
- 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.