Journal of the Korean Society of Mineral and Energy Resources Engineers ISSN:2288-0291(Print) 2288-2790(Online) 한국자원공학회지

Shallow 3-D seismic reflection techniques have been applied to image subsurface structure at a ground subsidence area in an old coal mine. Since the groundroll is predominant over the reflection signals, we could identify the shallow reflections only at the far-offset traces, where the groundrolls exist at later time. Therefore, to extract the reflection at the near-offset traces, we need to suppress the groundrolls at these traces. Characteristic behaviors of the groundroll were investigated in frequency and spatial domain. The groundroll events are characterized as relatively low frequencies and low moveout velocities compared to the reflection events. Therefore, we may suppress the groundrolls by dip filtering and enhance the reflections by frequency whitening. In 2-D data, the groundroll events appeared as linear; therefore, dip filtering in FK domain can successfully be applied. However, in 3-D data, the moveout curves of the ground rolls look like hyperbolic, therefore, in order not to damage the reflection signals, the processing scheme attacking the groundroll need to be applied only at the zone of groundrolls. Experiment shows that the groundrolls can be suppressed further by limiting the low frequency component in the wavelet transform domain.