Regional Variations in the Structure of the Upper Mantle and the Propagation of the Sa Phase

1966 ◽  
Author(s):  
J N Brune
Keyword(s):  
Upper Mantle ◽  
Regional Variations

Causes of regional variation of magnitudes

1971 ◽  
Vol 61 (3) ◽  
pp. 649-670 ◽  
Author(s):  
Ronald W. Ward ◽  
M. Nafi Toksöz
Keyword(s):  
Upper Mantle ◽  
Body Wave ◽  
Source Region ◽  
Spectral Ratio ◽  
Relative Difference ◽  
Body Waves ◽  
Regional Variations ◽  
Underground Nuclear Explosions ◽  
Short Period ◽  
Q Model

abstract Data from the short and long-period seismographs at the NORSAR in Norway are used to investigate the discrimination of earthquakes and underground nuclear explosions using surface-wave versus body-wave magnitude (Ms versus mb). Earthquakes and explosions occurring within the western United States and recorded in Norway exhibit either anomalously large surface waves or anomalously low compressional body waves compared to events from central Asia. These data, as well as the results of other investigators, indicate an anomaly of 0.8 to 1.0 in Ms or 0.6 to 0.8 in mb or some linear combination of the two. The mechanism producing anomalously large Ms values from a region for explosions and the cause of lower mb values are investigated in terms of stress relaxation triggered by an explosion and regional variations in attenuation in the upper mantle beneath both the source region and the receiver region. The method of short-period amplitude spectral ratio is applied to the records of the waves from five deep events to determine the difference in attenuation beneath different receivers. The relative Q model inferred from these data for the upper mantle from 50 to 750 km depth is QLASA = 75, QTFSO = 175, and QNORSAR = 390. The circum-Pacific island arc exhibits an apparent source attenuation asymmetry. The data from the mid-Atlantic ridge indicate that strong attenuation may be associated with parts of the ridge. The relative difference of the Q model between LASA and NORSAR results in a difference in mb of 0.40 for distances of 60° to 80°, which agrees well with the observed differences in mb. We conclude that regional variations of attenuation in the upper mantle play an important role in regional differences in Ms versus mb relationship.

Regional variations in deaths from volatile solvent abuse in Great Britain

Addiction ◽  
1997 ◽  
Vol 92 (12) ◽  
pp. 1765-1772
Author(s):  
A. Esmail ◽  
B. Warburton ◽  
J. M. Bland ◽  
H. R. Anderson ◽  
J. Ramsey
Keyword(s):  
Great Britain ◽  
Regional Variations ◽  
Solvent Abuse
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