APPLICATION OF SHALLOW SEISMIC REFLECTION METHODS IN NEOTECTONIC STUDIES: OBSERVATIONS ON DATA ACQUISITION, PROCESSING, AND INTERPRETATION

Shallow seismic reflection imaging is widely used to identify and characterize near-surface tectonic deformation in areas concerned with earthquake hazards. Because of the societal importance related to the results of these studies, considerable attention is required in acquiring, processing, and interpreting the data. An understanding of the characteristics of neotectonic deformation in an area, coupled with sufficient field testing (utilizing various seismic energy sources, receivers, and field geometries), helps support the collection of high-quality seismic reflection data. It is apparent that variations in geologic setting require changes to data acquisition parameters. Comparisons of compressional-wave (P-wave) and shear-wave (S-wave) reflection data show the importance of near surface lithology and saturation conditions (i.e., dry, water-saturated, or gas-charged) in controlling the quality of the acquired data. Processing steps that are effective on petroleum-industry seismic reflection data may actually have adverse effects when applied to shallow data sets. In most cases, if reflections can be identified on filtered shot gathers, carefully executed basic processing steps (including data editing, static corrections, and velocity analysis) will produce an accurate image of the subsurface and improve confidence in interpretation. Resolution and correct interpretation of neotectonic features on shallow seismic reflection profiles is greatly dependent on the ability to generate and record high-frequency seismic energy. However, because of their low velocity in comparison to P-waves (especially in water-saturated, unconsolidated sediments of the near surface), S-waves have the capability of providing high-resolution images even when their frequency is relatively low (~ 40-50 Hz).