Measurements of coda buildup and decay rates of western Pacific P, PO, and SO phases and their relevance to lithospheric scattering

B. Brandsdottir, W. H. Menke

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

We use empirical functions to characterize the shape of band-passed P, PO, and SO coda envelopes of 93 earthquakes. The data sets consist of earthquake data from the western and northwestern Pacific recorded by arrays of several stations and include both hydrophone and geophone recordings on analog and digital instruments. Each earthquake was band-passed into six octave-wide frequency bands between 0.8 and 50 Hz. The empirical function (a Poisson function, Pn(γ,t) = A γn+1tne-γt/n!) has parameters A (a measure of energy), γ (falloff rate), and n/γ (time of the maximum). The study showed that these parameters varied in systematic ways. PO/SO area (A) ratios were found to be considerably higher for hydrophone data in the 20°-35° range than for geophone and hydrophone data in the 8°-20° range. The difference was significantly larger than between vertical and hydrophone data in the same range. In some instances a strong frequency dependence or "reverse dispersion' of the time of maximum amplitude (n/γ) was observed, with the lower (1-2 Hz) frequencies arriving up to 25s later than the higher (10-20 Hz) frequencies, P, PO, and SO average falloff rates γ vary systematically with frequency, where the lowest frequencies most commonly have the minimum falloff rates and the middle frequencies have the maximum falloff rates. The variation in falloff between earthquakes is large, with the trends only becoming apparent upon averaging many measurements. -from Authors

Original languageEnglish
Pages (from-to)10541-10559
Number of pages19
JournalJournal of Geophysical Research
Volume93
Issue numberB9
Publication statusPublished - 1988

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