Fourier transformed amplitudes of the compressional waves
recorded between 9° and 91° (about 1000 to 10,000 km) epicentral
distance from Gnome, Shoal, Haymaker,and Bilby underground
nuclear explosions have been compared with Fourier transformed
amplitudes of P waves measured at distances between 9.0 and
1 3. 0 km from the explosions. Using a formula of the type
A= ε AoF(ξ)e - πfr/QV
apparent Qs have been computed for frequency ranges of 0.5 to
1.0 cps and 0.7 to 1.0 cps at the various epicentral distances. The
geometrical spreading factor F(ξ) and interface loss parameter ε
drop out of the computations when assumed to be frequency independent
in the narrow frequency pass-bands considered.
The computed apparent Q values indicate that the mantle
is inhomogeneous with respect to the absorption of seismic energy. Relatively low Q (high absorption) regions are centered around
25°, 42° and 74° and high Q (low absorption) regions are centered
around 20°, 31°, 71°, and 78° epicentral distances. These are
superimposed on a gradually increasing Q with epicentral
distance trend. The average apparent Q value for the upper
mantle is found to be 286 ± 38. The highest Q value of this
study occurs between 78° and 80° epicentral distance where it is
greater than 3000.
The high and low Q values obtained in this investigation
are of the same order of magnitude as those reported by other
investigators from body wave studies and the general variation of
the absorption properties with depth agrees reasonably well with
those obtained from surface wave studies. The depth of great
increase in electrical conductivity and the observed maximum
depth of earthquake foci both agree roughly with a region of large
increase in Q in the upper mantle. A relatively high absorption
zone is found to occur below this depth. / Graduation date: 1967
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28109 |
| Date | 19 August 1966 |
| Creators | Sarmah, Suryya Kanta |
| Contributors | Berg, Joseph W. Jr. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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