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Deep structures of the southern Tyrrhenian basin and P-wave residuals at Messina

ISTITUTO GEOFISICO E GEODETICO UNIVERSITÀ DI MESSINA, 98100 MESSINA, Italy

Abstract

In this article, P travel-time residuals for the Messina station are analyzed in order to investigate the Tyrrhenian upper mantle, which is considered to be crossed by a lithospheric slab.

A first set of 24 residuals derived from deep earthquakes of the southern Tyrrhenian Sea show early arrivals of, on the average, –1.3 sec at Messina. In addition, these negative residuals are associated with initial motion of the dilatation type. On the contrary, the few deep earthquakes which produce, as first motion, a compression at the Messina station, are associated with late arrivals of about 1 sec. These results are considered and discussed in order to analyze the hypocentral mechanism and P-wave transmission through the lithospheric slab.

A second and wider analysis is then extended to 206 earthquakes which have, with respect to Messina, an epicentral location in the distance range 16° to 103° and azimuthal orientation Z in the interval 180° to 380°. The first conclusion from this analysis is that the P travel times observed at Messina for epicentral distances in the range 20° to 103° and 245° Z 380° are generally 0.5 to 3 sec less than those given in the Jeffreys-Bullen tables.

Finally, a further improvement on the foregoing result has been obtained. This gives further confirmation of the consistency of regional variations of the P travel times with a slab model for the Tyrrhenian deep structures. As a matter of fact, the comparison between the travel times of Messina and a standard provided by observations in the stations of Rome and Trieste confirms early arrivals of about 1 sec on the seismic paths which cross the upper mantle in the southern Tyrrhenian region.

This article has been cited by other articles:

				A. BOTTARI and B. FEDERICO Estimate of the focal depth of deep earthquakes and some structural implications for the deep seismic activity in the Tyrrhenian region Bulletin of the Seismological Society of America, August 1, 1979; 69(4): 1193 - 1208. [Abstract] [PDF]