| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
LAMONT GEOLOGICAL OBSERVATORY COLUMBIA UNIVERSITY, PALISADES, NEW YORK
Abstract
Certain normally and inversely dispersed wave trains appearing in the interval between P and S at moderate epicentral distances are identified as specific higher leaking modes. Observed periods of normally dispersed wave trains vary from 7 to 5 sec and from 12 to 9 sec; observed periods of inversely dispersed wave trains increase from about 15 to 35 sec. While the normally dispersed wave trains are generally observed at epicentral distances less than 20°, the inversely dispersed wave trains may be observed at distances up to about 50°. This latter type of wave, with group velocities between 7.0 and 8.5 km/sec, is shown to be controlled by upper mantle structure, and thus represents a possible tool for upper mantle investigations. These waves differ from waves of the Rayleigh and Love modes in that they are more sensitive to the compressional velocity structure than to the shear velocity structure of the waveguide.
PL and shear-coupled PL data which are identified with the fundamental leaking mode were obtained for two paths in South America. Crustal thicknesses for the path between Buenos Aires and Rio determined independently from PL, shear-coupled PL and Rayleigh wave data agree well with one another. An analysis of the method of obtaining phase and group velocity curves consistent with the shear-coupled PL data shows that this method and this type of data together provide a high degree of precision for the determination of phase velocity curves.
In the theoretical treatment, a rapid, approximate method, which is basically Haskell's (1962) method, was used to obtain dispersion curves for the leaking modes. The results of this method are virtually identical to those of Gilbert (1964) and those of Oliver and Major (1960). The main advantage of the present method is that it provides additional information on particle motion and on the relative amplitudes of the predicted arrivals as functions of phase velocity and period.
This article has been cited by other articles:
|
|
 |
|
  J. Zhang and C. A. Langston Array observations of the shear-coupled PL wave Bulletin of the Seismological Society of America, April 1, 1996; 86(2): 538 - 543. [Abstract] [PDF]
|
|
|
|
|
|
R. A. W. HADDON Computation of synthetic seismograms in layered earth models using leaking modes Bulletin of the Seismological Society of America, August 1, 1984; 74(4): 1225 - 1248. [Abstract] [PDF]
|
|
|
|
|
|
G. A. BOLLINGER Attenuation of the Lg phase and the determination of mb in the southeastern United States Bulletin of the Seismological Society of America, February 1, 1979; 69(1): 45 - 63. [Abstract] [PDF]
|
|
|
|
|
|
C. A. LANGSTON The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves Bulletin of the Seismological Society of America, February 1, 1978; 68(1): 1 - 29. [Abstract] [PDF]
|
|
|
|
|
|
D. M. STALMACH and J. CL. DE BREMAECKER Body waves as normal and leaking modes: Dispersion and excitation on the (+ -) sheet Bulletin of the Seismological Society of America, June 1, 1973; 63(3): 995 - 1011. [Abstract] [PDF]
|
|
|
|
|
|
G. POUPINET and C. WRIGHT The generation and properties of shear-coupled PL waves Bulletin of the Seismological Society of America, December 1, 1972; 62(6): 1699 - 1710. [Abstract] [PDF]
|
|
|
|
|
|
D. V. HELMBERGER Long-period body-wave propagation from 4{degrees} to 13{degrees} Bulletin of the Seismological Society of America, February 1, 1972; 62(1): 325 - 341. [Abstract] [PDF]
|
|
|
|
|
|
A. M. DAINTY Leaking modes in a crust with a surface layer Bulletin of the Seismological Society of America, February 1, 1971; 61(1): 93 - 107. [Abstract] [PDF]
|
|
|
|
|
|
A.-B. K. IBRAHIM Leaking and normal modes as a means to determine crust-upper mantle structure for different paths to Sweden Bulletin of the Seismological Society of America, August 1, 1969; 59(4): 1695 - 1712. [Abstract] [PDF]
|
|
|
|
|
|
R. CHANDER, L. E. ALSOP, and J. OLIVER On the synthesis of shear-coupled PL waves Bulletin of the Seismological Society of America, December 1, 1968; 58(6): 1849 - 1877. [Abstract] [PDF]
|
|
|
|
|
|
F. ABRAMOVICI Diagnostic diagrams and transfer functions for oceanic wave-guides Bulletin of the Seismological Society of America, February 1, 1968; 58(1): 427 - 456. [Abstract] [PDF]
|
|
|
|
|
|
V. GREGSON JR< A model study of elastic waves in a layered sphere Bulletin of the Seismological Society of America, October 1, 1967; 57(5): 959 - 981. [Abstract] [PDF]
|
|
|
|
|
|
J. CL. DE BREMAECKER Body waves as normal and leaking modes. Part I: Introduction Bulletin of the Seismological Society of America, April 1, 1967; 57(2): 191 - 198. [Abstract] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
