Bulletin of the Seismological Society of America
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Bulletin of the Seismological Society of America; August 1969; v. 59; no. 4; p. 1695-1712
© 1969 Seismological Society of America
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Leaking and normal modes as a means to determine crust-upper mantle structure for different paths to Sweden

ABOU-BAKR K. IBRAHIM*

SEISMOLOGICAL INSTITUTE UPPSALA UNIVERSITY, UPPSALA, Sweden

Abstract

By using the leaking and normal mode dispersion curves, the average crustal and upper mantle structure is determined for seven different paths. The paths originate from earthquakes in Greece, Turkey, West Pakistan, Tibet, Kamchatka, Kurile Islands and Mexico. Records from Uppsala and Umeå, Sweden, are used. The characteristics of the leaking modes at different distances are examined. Surface waves are used to put more constraint on the models chosen using only the leaking wave data and to verify their mode of propagation.

A good fit for observational data of both the leaking mode (PL or PLH2) and the normal mode (Rayleigh) is found to one model for each path. The average crustal structures from Greece and Turkey to Uppsala are identical. The crustal and upper mantle models for paths from Tibet, West Pakistan, Kamchatka and Kurile Islands have approximately the same velocities but different crustal thicknesses. The dispersion characters of Mexican and North American paths are similar, while the average crustal thickness for the Asiatic paths is 5-15 km greater than for the Mexican path.

Since the dispersions of the leaking and normal modes are explained by one and the same structural model, it indicates that our hypothesis about the propagation of the leaking waves is true, and that a substantial portion of the long-period wave trains between the P and S waves can be explained in terms of these leaking modes.

Footnotes

* On leave of absence from Gulf Research and Development Co., Pittsburgh, Pa. 15230.






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