Accession Number : ADA325808

Title :   Seismic Sources and Structure in Iran and the Caucasus from Joint Seismic Program Array Data.

Descriptive Note : Final rept. 1 Oct 94-28 Feb 97,

Corporate Author : KANSAS UNIV LAWRENCE DEPT OF GEOLOGY

Personal Author(s) : Abers, Geoffrey A.

PDF Url : ADA325808

Report Date : APR 1997

Pagination or Media Count : 47

Abstract : Recently deployed seismic networks and arrays along the southern Former Soviet Union are characterized, including aspects of wave propagation that affect their ability to detect signals from the Iranian Plateau and surrounding regions. Signals at the Caucasus Network (CNET, deployed 1992-1994) were strongly affected by attenuation along paths that transect the Caucasus or Iranian Plateau, unlike signals to the north. At long paths (5-25 degree) the Caucasus and Iranian Plateau, little or no S wave energy was observed at frequencies above 0.5 Hz, and no discernable Lg. At distances > 10 degree few events smaller than m sub b < 4.5 were detectable. At shorter distances, analysis of body wave spectra were used to accurately quantify the attenuation boundary between the Greater Caucasus and Russian Platform. This transition serves as a proxy for that along most of the southern margins of Russia. Analysis of several hundred signals at distances < 4 degree showed a factor-of-3 decrease in attenuation from mountains to shield. These observations, at 1-15 Hz, suggest that signal amplitude at frequencies used for magnitude calibration will vary considerably from shield to mountains. The nature of this transition and its possible causes are discussed.

Descriptors :   *WAVE PROPAGATION, *SEISMIC WAVES, *ATTENUATION, FREQUENCY, USSR, SURFACE WAVES, MIDDLE EAST, SEISMIC DETECTION, MOUNTAINS, PLATFORMS, SIGNALS, SHIELDING, AMPLITUDE, IRAN.

Subject Categories : Seismology

Distribution Statement : APPROVED FOR PUBLIC RELEASE