Automatic detection of seismic phases using variance fractal-dimension trajectory

Abstract

Seismic refraction signals in crustal surveys are often contaminated by various types of noise mainly due to low- signal/noise Earth environments. A variance fractal-dimension technique is investigated and applied to real data sets for detection of seismic refraction signals from background noise. The sharpness of transition features on the variance fractal- dimension trajectory was used as a criterion for distinguishing the seismic signals, and a window size of 48 samples and a window spacing of 8 sample intervals were chosen to calculate the fractal dimensions and to create the trajectories for subse- quent tests and detection of phases Pg, Pn, PmP, and ground roll. The real data tested in this study were obtained from the 1992 Abitibi--Grenville Lithoprobe high.resolution refraction and wide-angle reflection experiments. The transition criterion provides a robust and powerful tool for separating the real seismic-refraction signals from the background noise. In the case of Pg phase from the refraction profile fan-shot ab2, the variance fractal-dimensions are generally smaller for the refrac- tion signals (-1.25) compared to the background noise (-1.75).