Amplitude retrieval from correlations of the ambient seismic field

Abstract:

Understanding the attenuation and amplification on the seismic wave propagation is fundamental for study Earth crust, its water content, temperature, and geology in general. The surface waves amplitude and attenuation can be used to help unravel both elastic as well as anaelastic structure of the Earth. Today, amplitude studies are mainly focused on long period seismic signals generated from earthquakes. This aspect introduces a limitation because of lack of high frequency energy from teleseismic events, and their limited geometrical distribution. We present here recent developments to retrieve amplitudes from the ambient seismic field (ASF). Our aim is to obtain unbiased measure of high frequency amplitude, to reconstruct the anelastic structure of the crust and upper mantle, while considering the effects of elastic focusing and defocusing in our analysis. Our processing, aimed to limit the effect of non-isoptropic ASF source distribution of incoming noise energy is employed in calculating noise correlation in US. Furthermore, we try to avoid any modification of the coherent amplitude information while pre-processing seismic noise time series before correlation. The resulting estimated amplitudes mainly explain the effect of station-to-station propagation and can be used to invert for attenuation parameters on the crust and upper mantle, although significant detailed analysis is needed to account for focusing.