Influence of source radiation patterns on globally observed short-period magnitude estimates (m(b))

We investigated the effect of the radiation pattern on station and network magnitude estimates (m(b)) by using centroid-moment-tensor (CMT) solutions published by the seismological group at Harvard University. The magnitude d ata used in this study were P amplitudes provided by the Prototype Internat ional Data Center (PIDC). When relating the station magnitude residuals to the calculated relative radiation factors, we found a small but clearly obs ervable dependency. By compensating for this effect after inverting for sta tion corrections and new event magnitudes, we found that the variance of th e station magnitude residuals was reduced by about 2.6%. In parallel, we es timated a set of mean station corrections with and without corrections for the radiation pattern. Similarly, we recomputed the average network magnitu des (m(b)), which in some cases differed by up to 0.15 magnitude units from the uncorrected average network In, values. In conclusion, we found that t he effect of the source radiation pattern on the amplitudes used for m(b) e stimation on a global scale is relatively small compared to effects from ot her factors. Only about 24% of the predicted radiation pattern signal can b e found in the observed data. However, when best possible m(b), values are needed (e.g., to investigate magnitude relations or station corrections for specific ray paths), compensating for the radiation pattern will help to r educe the scatter.