Seismological evidence pertaining to the structure of the Earth's upper mantle

Nuttli, Otto W.

doi:10.1029/rg001i003p00351

Cited by 36 publications

(9 citation statements)

References 79 publications

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“…It is quite recently that such anomalous structure has been generally recognized [see also Kanamori, 1970b]. In review papers dealing with lateral inhomogeneities of the upper mantle published a few years ago [e.g., Nuttli, 1963;Bath, 1965], only scraps of information about the anomalous structure of island arcs were presented. Although some structural models have been considered in individual studies, a model that attempts to account for the known observational facts reasonably well is given in Figure 16.…”

Section: Discussionmentioning

confidence: 99%

Seismological evidence for anomalous structure of island arcs with special reference to the Japanese region

Utsu¹

1971

Reviews of Geophysics

175

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Evidence indicating lateral heterogeneity in the deep structure of island arcs has been collected from seismological literature. Abundant evidence from seismological studies in Japan during the last fifty years generally supports the large‐scale anomalous structure beneath this typical island‐arc region, i.e., the existence of a high‐Q, high‐velocity zone about 100 km thick that dips from the vicinity of the trench beneath the arc to a depth of several hundred kilometers, and two low‐Q, low‐velocity zones in the upper mantle on the inner (continental) and outer (oceanic) sides of this dipping zone. Most of the seismic activity is confined to this dipping zone and to the crust near and on the inner side of the volcanic belt. In other island‐arc regions, such as Kurile‐Kamchatka, Indonesia, Tonga‐Kermadec, and New Zealand, a number of seismological studies have indicated the existence of similar anomalous structure. At present, more detailed, more accurate determination of the configuration and physical parameters of these anomalous zones by seismological techniques is in progress, providing important information for understanding the global tectonic process and the origins of regional geophysical and geological features found in island‐arc regions.

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Section: Discussionmentioning

confidence: 99%

Seismological evidence for anomalous structure of island arcs with special reference to the Japanese region

Utsu¹

1971

Reviews of Geophysics

175

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“…A few other reviews of traveltime models (Nuttli, 1963;Anderson, 1966;Hales and Herrin, 1972;and Massé, 1987), and several complete reviews on surface-wave studies (Ewing and others, 1957;Arkhangel'skaya, 1960;Nuttli, 1963;Bolt, 1964;Anderson, 1966;Kovach, 1966;Toksôz and others, 1967;Dorman, 1969;Bucher and Smith, 1971;Kovach, 1978;Knopoff, 1983) are available. The main contribution from the numerous available one-dimensional velocity models to our understanding of the upper-mantle structure of North America is in emphasizing the difference between the stable central and eastern half of the continent and the tectonically active western half of the continent.…”

Section: Discussion Of One-dimensional Velocity Modelsmentioning

confidence: 99%

“…An S-wave velocity model for the upper mantle of the continental United States, computed by Ibrahim and Nuttli (1967) using traveltime data, is not very different from Nuttli's (1969) model for the western United States. Both models have low-velocity zones at 150,350, and 670 km depths, rapid velocity increases at 400 and 700 km, and nearly constant velocity between 220 and 350 km and between 400 and 670 km.…”

Section: Models Of the Stable Continentmentioning

confidence: 93%

Chapter 29: Upper-mantle velocity structure in the continental US. and Canada

Iyer¹,

Hitchcock²

1989

Geological Society of America Memoirs

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The available studies on upper-mantle structure in North America can be broadly divided into two categories: delineation of one-dimensional models, that is, the determination of P-and S-velocities as a function of depth; and computation of two-and three-dimensional models to take into account lateral heterogeneities in structure. About 50 one-dimensional models based on traveltimes, synthetic seismograms, and surfacewave velocities are currently available for continental North America. The gross features of these models are sharp velocity increases at depths near 400 and 650 km in the upper mantle beneath the whole continent and the presence of a low-velocity layer in the uppermost part of the upper mantle in the western half of the continent. A few other velocity discontinuities and velocity-gradient changes have also been documented. The most important finding from the available studies is a quantitative confirmation of what was suspected even in the early 1950s, namely, that the upper-mantle structure, particularly the structure related to the low-velocity layer, is drastically different in the tectonically active Cordillera from the stable central and eastern shield of North America. In western North America, in general, the upper-mantle velocities are low, and the lowvelocity zone is well developed and occurs at shallow depths. On the other hand, in the central and eastern parts of the continent the upper-mantle velocities are higher than in the west, and a low-velocity layer-if present at all-tends to be deep and to have a smaller velocity contrast than in the west. Available data and modeling techniques are inadequate to unambiguously resolve spatial variation in the depths to the 400-km and 650-km discontinuities and the boundaries of the low-velocity layer in North America. Apart from the broad division of the one-dimensional models into tectonically active and shield structures, any further finer scale quantitative division of the models within each tectonic unit is not warranted by the available data. Qualitatively, however, it is clear that such finer scale differences do exist, particularly in the upper 250 to 300 km of the upper mantle.The laterally heterogeneous structure of the upper mantle in North America has been studied by three-dimensional modeling using teleseismic P-and S-wave residuals. Three-dimensional inversion of P-and S-wave residual data collected over a substantial part of the North American continent show the existence of long-wavelength heterogeneous structure extending throughout the upper mantle. In addition, shortwavelength lateral heterogeneities are revealed by regional investigations. These include heterogeneous velocity structures associated with: (

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“…Sn velocity compiled by Nuttli (1963) It is quite likely that the regional variation of S velocity structure is about the same order as, or even more pronounced than, that of P velocity structure.…”

Section: Introductionmentioning

confidence: 99%

“…This paper describes the current state of our knowledge concerning the earths structure in special reference to the regional variation of the mantle. It is intended here to summarize the latest results for those who do not primarily specialize in seismology rather than to make an extensive review; for more general discussions on the related subjects reference can be made, for example, to Anderson (1965Anderson ( , 1967, Press (1964Press ( , 1966a, Kovach (1965), Nuttli (1963), Bolt (1963), Savarenskii (1966), and Toksoz et al (1967). (53) 1.…”

Section: Introductionmentioning

confidence: 99%

Seismological Evidence for Heterogeneity of the Mantle

Kanamori

1970

J. geomagn. geoelec

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The latest results concerning the depth variation of Q, P and S-wave velocities obtained by various seismological methods are reviewed with special emphasis on the regional variation.The body-wave travel time and the slope, dT/dd, have been inverted to obtain P-and S-wave velocity distributions within the mantle. The P velocity is now believed to be known with an accuracy of E 1% in the mantle below 1000km. In the upper mantle, a considerable difference has been found among different regions. The longperiod surface waves have been used to reveal the regionality of the upper mantle. Based upon the surface wave and body-wave results, it is now agreed that the mantle beneath shields has much higher seismic velocities than those beneath ocean and tectonically active regions. At such tectonically active regions as Japan, basin and range province of the western U. S. and the Pacific ocean side of South America, the upper mantle velocities have been found to be significantly lower than the average. Teleseismic P waves are delayed by 1.0 to 1.5 sec at tectonically active regions as compared with shields. The existence of the low-velocity zone for S waves in the sub-oceanic mantle is almost certain.The shape of the low-velocity zone varies markedly beneath continents. The distribution of Q with depth is not known in detail. However, it is almost certain that the value of Q is higher by more than one order of magnitude in the mantle below 1000km than in the mantle above. The average values of Qa (Q for P-waves) and Q (Q for S-waves) for the upper mantle range from 100 to 300. Horizontal heterogeneities as large as a few per cent in velocity and one order of magnitude in Q have been found beneath mid-oceanic ridges and island arcs. However, the uniqueness of the structure derived is still questionable.

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Seismological evidence pertaining to the structure of the Earth's upper mantle

Cited by 36 publications

References 79 publications

Seismological evidence for anomalous structure of island arcs with special reference to the Japanese region

Seismological evidence for anomalous structure of island arcs with special reference to the Japanese region

Chapter 29: Upper-mantle velocity structure in the continental US. and Canada

Seismological Evidence for Heterogeneity of the Mantle

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