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On the Stability of High Frequency Wave Regional Amplitudes: A Study of Middle Eastern Q models and Their Reliability

Descriptive Note:

[Technical Report, Final Report]

Corporate Author:

University of Missouri

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The objective of this work is to understand the origin of relatively large variations in Lg amplitudes that do not appear to be a first order effect of path, station, or source. We have investigated this variance by improving existing attenuation models for the northern Middle East by combining important new data sets, specifically data from the Syrian, Iraqi, and Iranian national networks, using a Reverse Two Station approach with a minimal number of assumptions. In order to evaluate our ability to remove path based and site-based effects on high frequency amplitudes, we are working to measure the inherent variation in the regional phase amplitudes. We have chosen to focus on Lg amplitudes since they have the highest signal to noise ratio for continental paths as well as coda throughout the northern Middle East. Furthermore, we are striving to understand the origin of this variance in order to more accurately predict direct phase amplitudes and also to understand the variance associated with each. We accomplished this by generating probability distributions of Qf for every reverse two station RTS path with a sufficient number of repeated paths. We have found a surprisingly large variation in RTS amplitude reduction. This result cannot be explained by variation in source radiation patterns or by site amplification terms neglecting azimuthal variation, Q anisotropy, or complexity of the scattered wave field.


Subject Categories:

  • Seismology
  • Radiofrequency Wave Propagation

Distribution Statement:

[A, Approved For Public Release]