On the Effect of Synthetic and Real Data Properties on Seismic Intensity Prediction Equations

The present investigation focuses on the effect of input data properties on the estimation of seismic intensity prediction equation (IPE) coefficients. Emphasis is placed on small-to-moderate magnitude earthquakes. Synthetic intensity data points (IDPs) are created using a given IPE, assuming independence of azimuth. Extensive simulations are performed for single earthquakes and a synthetic database. Tests of single earthquakes show that increasing the sample size narrows the range of obtained coefficients. The larger the difference between the shortest and longest distance of IDPs from the epicentre, the narrower is this range. A short radius of perceptibility is more rapidly saturated with new data points than a long one. The synthetic database is used to examine the effect of magnitude and depth errors. The performance of synthetic data gives a model with which the real data can be compared. The attenuation coefficient appears stable against magnitude errors of ± 0.2 units, but starts to be overestimated as magnitude errors increase. Assuming an erroneous regional depth easily leads to intensity differences of 1 degree. The mean coefficient values deviate from the correct ones and tend to increase with depth. The results resemble the synthetic ones, but imply larger uncertainties. The attenuation coefficient, ν, appears to be the least sensitive coefficient to errors. Real data from seven post-1965 earthquakes in the magnitude range of 4.0–5.2 were retrieved from the intensity database of the United Kingdom.