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Numerical seismograms of long-period body waves from seventeen to forty degrees

Helmberger, Donald V. (1973) Numerical seismograms of long-period body waves from seventeen to forty degrees. Bulletin of the Seismological Society of America, 63 (2). pp. 633-646. ISSN 0037-1106.

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Long-period wave propagation in the upper mantle is investigated by constructing synthetic seismograms for proposed models. A model consisting of spherical layers is assumed. Generalized ray theory and the Cagniard-de Hoop method is used to obtain the transient response. Preliminary calculations on producing the phases P and PP by ray summation out to periods of 50 sec is demonstrated, and synthetic seismograms for the long-period World Wide Standard Seismograph Network (WWSSN) and Long Range Seismic Measurement (LRSM) instruments are constructed. Models containing prominent transition zones as well as smooth models predict a maximum in the P amplitude near 20°. The LRSM synthetics are quite similar for the various models because the instrument is relatively narrow-band, peaked at 20 sec. The upper mantle appears smooth at wavelengths greater than 200 km. On the other hand, the WWSSN synthetics are very exciting for models containing structure. The triplications are apparent and the various pulses contain different periods. The amplitude of the P phase at 30° is down to about 25 per cent of its 20° maximum. The amplitude of the PP phase at 35° is comparable to P. Near 37°, the PP phase grows rapidly reaching about twice the P phase amplitude near 40°. Models containing sharp transition zones produce high-frequency interferences at neighboring ranges. A profile of observations is presented for comparison.

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Additional Information:Copyright © 1973, by the Seismological Society of America. Manuscript received September 14, 1972. This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Office of Scientific Research under Contract F44620-72-C-0078.
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Advanced Research Projects Agency (ARPA)UNSPECIFIED
Air Force Office of Scientific Research (AFOSR)F44620-72-C-0078
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Caltech Division of Geological and Planetary Sciences2189
Issue or Number:2
Record Number:CaltechAUTHORS:20140812-162944071
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48459
Deposited By: George Porter
Deposited On:13 Aug 2014 14:51
Last Modified:03 Oct 2019 07:04

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