Global upper mantle structure from long-period differential travel times

Journal Article · Wed Apr 10 00:00:00 EDT 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/90JB01445· OSTI ID:5447006

Woodward, R L; Masters, G ^[1]

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1. Univ. of California, San Diego (USA)

The authors have made over ten thousand measurements of PP-P and SS-S differential travel times from long-period Global Digital Seismograph Network recordings of all events with m{sub b} {ge} 5.5 which occurred during the years 1976 and 1986. The experiments indicate that lower-mantle structure and source-receiver structure can each contribute approximately {plus minus}0.5 s to the measured PP-P residuals so there is considerable signal to be explained. The pattern observed in the PP-P measurements is similar to the pattern observed in the SS-S measurements, with the SS-S residuals 2 to 4 times larger in magnitude. Comparisons of measured residuals to those predicted by the upper-mantle models of Woodhouse and Dziewonski show that the overall patterns are quite similar but the amplitude of the model residuals is roughly a factor of 2 too small. Comparisons with the predictions of a whole-mantle model of Tanimoto again shows that the predicted pattern of residuals is reasonably consistent with the observations but now the predicted residuals are too large by about a factor of 2. They have also binned the measurements according to the tectonic regionalization GTR1 of Jordan and find a qualitative correlation of average residual with tectonic region. In particular, Precambrian shields show a strong anomaly, and there is a correlation of residual size with the age of oceanic crust at the bounce point. For all tectonic regions the ratio of SS-S to PP-P residuals is approximately 2. This ratio is consistent with a thermal origin for the observed signal. Finally, measurements show no compelling evidence for azimuthal anisotroph which might be related to fossil spreading direction or the direction of absolute plate motion.

• OSTI ID: 5447006
• Journal Information: Journal of Geophysical Research; (United States), Vol. 96:B4; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
EARTH MANTLE
GEOLOGIC STRUCTURES
SEISMIC SURVEYS
ANISOTROPY
CORRELATIONS
DATA ANALYSIS
EARTHQUAKE MAGNITUDE
EARTHQUAKES
GEOLOGIC MODELS
GEOMORPHOLOGY
GLOBAL ASPECTS
OCEANIC CRUST
PLATE TECTONICS
PRECAMBRIAN ERA
SEISMIC P WAVES
SEISMIC S WAVES
TECTONICS
EARTH CRUST
GEOLOGIC AGES
GEOLOGY
GEOPHYSICAL SURVEYS
SEISMIC EVENTS
SEISMIC WAVES
SURVEYS
580000* - Geosciences