Accession Number:

ADP204476

Title:

Seismic Sources and Structure in Iran and the Caucasus from Joint Seismic Program Array Data,

Descriptive Note:

Corporate Author:

KANSAS UNIV LAWRENCE DEPT OF GEOLOGY

Personal Author(s):

Report Date:

1995-08-14

Pagination or Media Count:

7.0

Abstract:

Amplitudes of seismic waves recorded at the Caucasus network, along the north flanks of the Greater Caucasus, are measured and analyzed for attenuation characteristics. From one year of observation, 96 events between 1 and 10 from the network provide stable measures of RMS Pn, Sn, Lg, and late coda amplitudes. Measurements were taken from seismograms filtered at several narrow frequency bands centered from 0.5 to 8.0 Hz, where signal levels are highest. Our results confirm previously-inferred spatial variations in Sn and Lg attenuation, that the Greater Caucasus marks an abrupt boundary between the high-Q Russian Platform and a region of exceedingly poor Sn and Lg propagation within the collision belt. Paths that cross large Quaternary volcanic provinces, along the Greater Caucasus, seem most affected. Amplitude ratios show the largest regional differences in the 1-2 Hz range and decrease at higher frequencies, and indicate complicated changes in the mechanism of attenuation between shield and tectonic paths. For a given path the RMS amplitudes of the Lg group and late coda phases predict magnitudes as well as can be expected from mb uncertainties. However biases of 1.0-1.5 magnitude units are seen for RMS amplitudes along different paths, at frequencies higher than 1 Hz. Variation is much reduced by taking 3-component and network averages of amplitude measurements.

Subject Categories:

  • Government and Political Science
  • Seismology
  • Seismic Detection and Detectors
  • Nuclear Weapons

Distribution Statement:

APPROVED FOR PUBLIC RELEASE