Do seismologists agree upon epicentre determination from macroseismic data? A survey of ESC Working Group ' Macroseismology'

Abstract

In contrast to the case of instrumental data, the procedures for epicentral parameter determination (coordinates and I0) from macroseismic data are not very well established. Although there are some "rules", upon which most seismologists agree (centre of the isoseismal of largest degree, and so on), the practical application of, such rules displays many problems. Therefore, it is commonly seismologists' practice to find their own pro cedures and solutions; this is particularly evident in the more complicated cases, Such as offshore epicentres or, as in many cases of historical earthquakes, poor sets of data. One of the major consequences is that parametric catalogues are not homogeneous with respect to macroseismic parameters; moreover, merging catalogues compiled according to different criteria can introduce high noise in any catalogue built in such a way. In order to survey the current practice of epicentre determination from macroseismic data in Europe, a set of cases was distributed to the participants of the first meeting of the ESC WG "Macroseismology". A comparison of the 15 sets of results provided by 16 authors, who gave their own solutions and the explanation., of the adopted procedures is given, showing that in some cases the ideas and results are rather distant.