Analysis of the CROP-04 seismic data

The analysis of the Apennine CROP-04 seismic data has been carried out to understand the causes of a very poor field data quality and then to guide possible re-processing efforts. We study both the vibroseis recordings and the few explosive data available and we compare the signal to noise ratio of the seismic signals with either the employed acquisition parameters and the geology and topography at the surface. The geological complexity of the area with the many tectonic disturbances associated with the thrusting and the faulting causes a diffused wave-field scattering that degrades the S/N ratio of both the vibroseis and the explosive recordings. However we found additional problems, especially for the vibroseis data. In fact, the vibroseis source does not insure the necessary penetration of the seismic signal and in several recordings yields first breaks that are difficult to pick due to the precursors. This constitutes a problem for refraction statics computation. The excessively long receiver spread is not appropriate to the rapid variations of the surface lithologies, that cause abrupt velocity changes, and of the topographic elevations along the profile. When strong surface wave noise is present, the receiver group interval does not appear to fulfil the necessary sampling requirements and thus severe aliasing effects are encountered. The high tortuosity of segments of the field layout, also due to the location of the vibroseis trucks along the available mountain roads, renders troublesome the CMP gathering operation during the processing phase. Finally, the presence on the vibroseis data of a significant amount of noisy traces, especially at far offsets, strongly biases the overall quality of the dataset.