1_Chapter1 - 10 Chapter 1 Introduction From seismological...

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10 Chapter 1 Introduction From seismological point of view, the interior of the earth can be divided into several distinct layers (crust, mantle and core), considered as a system of horizontal layers affecting the seismic energy arriving at a given station. Only the uppermost part of the crust is available for direct sampling from boreholes. At greater depths all information about its composition is indirect. Much of our information about the earth's interior has been derived from a knowledge of the variation of seismic velocities with depth. Consequently, the recorded motion at the earth's surface depends on the elastic parameters, the thickness of these layers, as well as on the existing seismic energy and the recording instrument. The first accurate teleseismic recording was obtained in 1889 in Potsdam, Germany, 15 minutes after an earthquake in Japan (von Rebeur-Paschwitz, 1889), while the beginning of the systematic collection of global seismic data was started in 1892 by John Milne (Milne, 1895) who developed a seismometer that was sufficiently compact to be installed in about 40 observatories around the world. The first attempt to investigate the structure of the earth from transmission times of earthquakes was made by Oldham (1906) who discovered the earth's core. On the other hand, the efforts to determine crustal thickness dates back to 1910, when Mohorovicic first identified an abrupt increase in velocity beneath the shallow rocks under Europe. The boundary separating crustal rocks from mantle rocks is now called as the Moho. The depth of the Core-Mantle boundary was delineated accurately by Gutenberg (1913), who also investigated in 1958, the surface amplitude and polarizations of incident SV waves and the amplitudes of the SH components from the recorded S waves, assuming that the crust and the upper mantle could be represented by a simple half-space model.
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11 In the 1950s and 1960s, the spectral analysis of long-period data was the major subject to study the crustal structure using teleseismic records besides controlled source techniques. The theoretical background of the spectral analysis method was presented by Thomson (1950) and Haskell (1953) as a matrix formulation. Phinney (1964), used Haskell's matrix method to calculate the spectral response of a layered crust to compare observed long period P-wave spectra from distant earthquakes recorded at Albuquerque and Bermuda. Most recently, Al-Amri, Necioglu and Mokhtar (1996), used the spectral analysis
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This note was uploaded on 05/09/2010 for the course EARTH SCIE APPLIED GE taught by Professor Es during the Spring '09 term at IIT Bombay.

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1_Chapter1 - 10 Chapter 1 Introduction From seismological...

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