Blackwell Publishing Journal Backfiles 1879-2005
The particle motion of regional arrivals is frequently treated in automatic phase-recognition schemes as that appropriate to simple P or S waves incident on an elastic, laterally homogeneous half-space. This model implies that the motion in ‘P-type’ phases can be described in terms of a single, generalized signal process and ‘S-type’ phases in terms of two independent processes (SV and SH) and thus, all regional arrivals could be fully characterized by three components of motion. In this paper, we present anlyses of the particle-motion patterns of various regional arrivals recorded at the ARCESS array from closely spaced events in the Kola Peninsula. We have found that only Pn-particle motion, described in terms of two independent signal processes, can be reliably characterized by three-component recordings. On the other hand, the various regional arrivals following Pn, such as Pg and Sn and Lg, can only be poorly characterized on the basis of three-component recordings alone. The reason is that these arrivals must be described in terms of more than two independent generalized signal processes, at least three for Pg and Sn, and possibly up to five for Lg. Recognition of these phases will thus require the use of more sensors than signal processes in the observing sensor configuration, such as three-component sensors combined with a small tripartite array. We have investigated the feasibility of adaptive, automatic recognition of regional arrivials by a wavefield extrapolation scheme utilizing such a mini-array. The process, which appear to be promising, adaptively learns the particle-motion patterns of individual arrivals, including complex site-response functions, from examples of closely located regional events.
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