- Ground-motion model is:
where PGA is in m∕s2, c1 = -2.09, c2 = 0.47, c3 = -0.039 and σ = 0.3 (note that the method given in
the article must be followed in order to predict the correct accelerations using this equation).
- Uses data (186 records) of Ambraseys and Douglas (2000, 2003) for Ms ≥ 5.8. Add 57 records from
ISESD (Ambraseys et al., 2004) for 5.0 ≤ Ms ≤ 5.7.
- Investigates whether ‘magnitude-dependent attenuation’, i.e. PGA saturation in response to increasing
magnitude, can be explained by PGA approaching an upper physical limit through an accumulation of
data points under an upper limit.
- Proposes model with: a magnitude-independent attenuation model and a physical mechanism that prevents
PGA from exceeding a given threshold. Considers a fixed threshold and a threshold with random
- Develops the mathematical models and regression techniques for the truncated and the randomly clipped
- Reduces number of parameters by not considering site conditions or rupture mechanism. Believes following
results of Ambraseys and Douglas (2000, 2003) that neglecting site effects is justified in the near-field
because they have little effect. Believes that the distribution of data w.r.t. mechanism is too poor to
- Performs a standard one-stage, unweighted regression with adopted functional form and also with form:
log 10(PGA) = c1 + c2M + c3r + c4Mr + c5M2 + c6r2 and finds magnitude saturation and also decreasing
standard deviation with magnitude.
- Performs regression with the truncation model for a fixed threshold with adopted functional form. Finds
almost identical result to that from standard one-stage, unweighted regression.
- Performs regression with the random clipping model. Finds that it predicts magnitude-dependent
attenuation and decreasing standard deviation for increasing magnitude.
- Investigates the effect of the removal of high-amplitude (PGA = 17.45m∕s2) record from Tarzana of the
1994 Northridge earthquake. Finds that it has little effect.