Focal depth determination using macroseismic data

(in Croatian)

Abstract

The macroseismic intensity – distance relation (Eq. 6) is defined through four parameters: coefficient p, epicentral intensity I_o, focal depth h and absorption coefficient. All the known methods for parameter estimation were based on “a priori” knowledge of the epicentral intensity and/or used a graphical procedure. Also, the epicentral intensity was taken as discrete variable and the value to the coefficient p was assigned in advance. By considering the epicentral intensity as a continuous variable that can achieve any value greater or equal to the maximum observed intensity, it was possible in this paper to apply the least squares method for parameters determination. The only assumption is that the starting values of the parameters, that are to be determined, are roughly known. The procedure consists in calculating the corrections to the starting values of parameters until the best fit, in the sense of Eq. (17), is obtained. In this way the focal depth determination does not depend on the assumptions contained in the assignment of the epicentral intensity, and the imprecision of the graphical method is avoided. The method could be applied for the determination of any combination of the parameters of Eq. (6), providing that the number of observed isoseismal radii is not less than the number of the parameters to be estimated. In the cases where the number of observed isoseismal radii exceeds the number of the parameters to be estimated, the error estimation is also possible, giving the quantitative measure of the precision of the results obtained. Due to the flexibility of the method and its applicability to the electronic computer the parameter estimation is much faster and more precise than before.