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17002 results

Page 184 of 851

  • 3 - Inner Core Surface and Its Interior

  • Hrvoje Tkalčić, Australian National University, Canberra
  • Book:
    The Earth's Inner Core
    Published online:
    26 January 2017
    Print publication:
    02 February 2017, pp 38-73

  • Summary

    “Because the modes of group 2 would have zero energy in the inner core if it were liquid, the only way to increase their eigenfrequencies would be to increase the bulk modulus in the outer core, a condition contradicting that necessary to satisfy the data of group 1. We therefore conclude that solidity of the inner core represents the only solution consistent with the observations of normal modes.”

    Adam M. Dziewoński & Freeman Gilbert (Dziewoński and Gilbert, 1971)

    Introduction to Studies of the IC Surface and Its Interior

    A simple glance at a tomogram derived through use of modern imaging techniques reveals a stunning variety of features within the Earth's interior. Some local and regional studies of the Earth's crust use the portion of the seismic wavefield with wavelengths of several kilometres, while other, usually global, studies concentrate on wavelengths that exceed hundreds or even thousands of kilometres. When the focus of study is shifted to larger depths, images of the deep Earth's interior are often blurry, lacking the level of detail obtained nearer the Earth's surface. Tomography often does not extend to the Earth's core. If we were equipped with a toolset similar to that used for imaging near the Earth's surface, and if we were able to apply those tools to the well-mixed OC, the images would most likely reveal homogeneous seismological structure at long wavelengths. But what about the solid IC, which sits in its centre? The IC's radius is comparable in length to IC-sensitive long wavelength waveforms and normal modes, which are sensitive to IC structure only as part of an integral over the rest of the planet's radius. Yet, we have progressed significantly in understanding the physical appearance of the Earth's IC, not just at its surface, but also deep in its interior. Questions including how the IC appears at its surface, whether it has a rough or smooth boundary, whether it contains topography, how it solidifies and at what rate, what the density contrast at the OC boundary is, and how the IC texture changes with distance from the ICB have been the driving force behind many IC studies.

Asteroids
  • Astronomical and Geological Bodies
  • Thomas H. Burbine
  • Published online:
    01 February 2017
    Print publication:
    15 December 2016
  • Asteroid science is a fundamental topic in planetary science and is key to furthering our understanding of planetary formation and the evolution of the Solar System. Ground-based observations and missions have provided a wealth of new data in recent years, and forthcoming missions promise further exciting results. This accessible book presents a comprehensive introduction to asteroid science, summarising the astronomical and geological characteristics of asteroids. The interdisciplinary nature of asteroid science is reflected in the broad range of topics covered, including asteroid and meteorite classification, chemical and physical properties of asteroids, observational techniques, cratering, and the discovery of asteroids and how they are named. Other chapters discuss past, present and future space missions and the threat that these bodies pose for Earth. Based on an upper-level course on asteroids and meteorites taught by the author, this book is ideal for students, researchers and professional scientists looking for an overview of asteroid science.

The Earth's Inner Core
  • Revealed by Observational Seismology
  • Hrvoje Tkalčić
  • Published online:
    26 January 2017
    Print publication:
    02 February 2017
  • The inner core is a planet within a planet: a hot sphere with a mass of one hundred quintillion tons of iron and nickel that lies more than 5000 kilometres beneath our feet. It plays a crucial role in driving outer core fluid motion and the geodynamo, which generates the Earth's magnetic field. This book is the first to provide a comprehensive review of past and contemporary research on the Earth's inner core from a seismological perspective. Chapters cover the collection, processing and interpretation of seismological data, as well as our current knowledge of the structure, anisotropy, attenuation, rotational dynamics, and boundary of the inner core. Reviewing the latest research and suggesting new seismological techniques and future avenues, it is an essential resource for both seismologists and non-seismologists interested in this fascinating field of research. It will also form a useful resource for courses in seismology and deep Earth processes.

Page 184 of 851