Locating regional seismic events with global optimization based on interval arithmetic

Abstract

More than 1000 seismic events in northern Europe at distances of up to 400 km for the detecting network are located using an optimization method in which the global minimum of the traveltime function residuals is searched for using an Interval Arithmetic (IA) method. Epicentres are determined using P waves detected by the Finnish national seismic network: up to 15 stations were used in the analysis. The IA results coincide with locations provided by the University of Helsinki bulletins with a median location bias of 7.6 km. A second data set of 59 explosions in the Siilinjarvi mine in central Finland was examined in detail, because the locations of the explosions were known exactly. In this case, the median difference of IA locations was 3.8 km from the average location of mine explosions, while all 59 events were located within 9 km of the 'true' epicentres. The corresponding median error of the University of Helsinki locations was smaller (3.2 km), but some Helsinki locations were well over 10 km from the mine. The convergence towards the global optimum using interval arithmetic was fast when compared with the conventional least-squares approaches for epicentre determinations.