Moho reflections within seismic noise autocorrelations

Abstract

The noise recorded at a seismic station has information about some properties of the medium such as their discontinuities. The depth of these changes in velocity can be retrieved using auto-correlation and stacking methods applied to the seismic noise. We developed a new method to constrain Moho reflections hidden within the autocorrelation of seismic noise. This is done by filtering the data in different frequency bands (each one defined by a central frequency), applying the auto-correlation and stacking process per central frequency and finally stacking the frequencies of interest. Synthetic tests showed that phases associated with a discontinuity at depth arrive at the same lag time across different frequencies, while side lobes and constructive interactions of the random noise have time shifts in the lag time. We tested the method using data from the MASE array installed in Central Mexico and the results show a good agreement with previous works. We found that exploring the frequency content with different bandwidth filters and stacking only those with useful information helps to improve the SNR and to find the phase associated with the Moho discontinuity at depth.