Marine substrate response evaluation from seismic attributes: A case study using CHIRP

Abstract

This paper presents an evaluation of the response of seismic attributes in different types of marine substrates (rock, shallow gas, sediments). In the analyses of seismic profiles attributes were chosen considering wave parameters, like amplitude and frequency (Instantaneous Amplitude, RMS Amplitude, Energy (amplitude) and Instantaneous Frequency). The seismic profiles were acquired using a CHIRP sub-bottom profiler, which was a non-impulsive source with a frequency ranging between 2 and 16 kHz (model SB-216S of Edgetech). The statistical method used was the non-parametric Kruskal-Wallis analysis, which was consisted of two parts: (a) the comparison of seismic attributes behavior between marine substrates, as unconsolidated sediments, rock and shallow gas; and (b) the comparison of seismic attributes behavior between different grains sediment classes (sub-grouped according sorting). Comparing sediments, shallow gas and rock the amplitude related attributes were effective in distinguishing sediments from shallow gas/rock, but did not differentiate rock from shallow gas. This result could be explained because, despite they had very high amplitudes, these amplitudes were similar to each other. In the other hand, the Instantaneous Frequency attribute was effective in differentiating sediments, rock and shallow gas, with sediments showing higher frequency range, rock an intermediate range and shallow gas the lowest of them. Related to grain size classes and sorting, statistical analysis showed that it was possible to separate samples in two distinct groups, when comparing the attribute values: The SVFS group (silt and very fine sand) and the SFMC group (fine, medium and coarse sand). Using a Spearman coefficient it was found that the Instantaneous Amplitude attribute was more efficient to separate the two groups. None of the attributes was able to distinguish between the nearest grain size classes, as between silt and very fine sand.