Development of Surface Wave Dispersion and Attenuation Maps and Improved Methods for Measuring Surface Waves

摘要

The objective of this project is to optimize surface wave measurements, particularly at regional and local distances, and over the high frequency period band of 8-15 seconds. There are three main parts to this study: 1) We collect and then invert Eurasian surface wave amplitude data for attenuation and Q structure; 2) we develop amplitude corrections using the Born approximation and then compare them with observations and with the results of finite difference calculations; 3) we develop a time domain path corrected surface wave magnitude and compare it with other surface wave magnitudes. In addition, we analyze the surface waves from the North Korean nuclear test of October 9, 2006. The path corrected surface wave magnitude is similar to the Butterworth filtered magnitude developed by Russell, but regionalized to take into account variations in earth structure and attenuation. We conclude that the Born approximation is of marginal value for attenuation studies because it is a small perturbation approximation and the observed amplitude variations are too large and complicated to be predicted by the Born approximation. We find that the average surface wave Q of Eurasia is lower than our previous background model, particularly along a band running through the Middle East. We develop attenuation maps that predict attenuation along any path in Eurasia for frequencies below 0.15 Hz for distribution to AFRL, the DOE Knowledge Base and other researchers.