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New evidence for a change in physical conditions at depths near 100 kilometers

Gutenberg, B. and Richter, Charles F. (1939) New evidence for a change in physical conditions at depths near 100 kilometers. Bulletin of the Seismological Society of America, 29 (4). pp. 531-537. ISSN 0037-1106.

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Comparative investigation of the seismograms of shallow earthquakes shows that the amplitudes of the first recorded longitudinal wave (Pn or P) vary considerably with distance from the epicenter. At distances up to 6° the seismograms are of "local shock" type, and the amplitude of Pn increases somewhat with distance. From 6° the amplitude decreases regularly, reaching a very small minimum near 14° (1500 km.). There is then a sudden increase, and the amplitudes continue large to beyond 20°. Together with the corresponding travel times, this suggests that at about 80 km. below the surface the velocity of longitudinal waves ceases to increase with depth, and probably decreases slightly through a limited range of depth, below which it again increases with depth. It is not yet settled whether the decrease is gradual throughout its range, or whether it takes place suddenly at a discontinuity.

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Additional Information:Copyright © 1939, by the Seismological Society of America. Manuscript received for publication June 23, 1939.
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Balch Graduate School of the Geological Sciences Contribution277
Issue or Number:4
Record Number:CaltechAUTHORS:20140804-163129443
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47947
Deposited By: George Porter
Deposited On:05 Aug 2014 15:14
Last Modified:03 Oct 2019 06:58

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