Common-transmission gather for direct seismic attenuation indication

Abstract

When seismic waves illuminate the subsurface medium and propagate back to the surface geophones, they bring back attenuation information (in terms of quality factor [Formula: see text]) related to the subsurface viscoelastic features. Such information can be reflected by high-frequency component loss, phase change, and amplitude decay. We develop a novel method of common-transmission gather (CTG) to directly indicate the subsurface seismic attenuation features. The CTG is defined as a group of traces with a range of subsurface offsets that contain all the seismic signals transmitting the same subsurface location. We first focus the surface seismic data backward on one selected horizon, such as one reservoir seal, using the wave equation redatuming approach. This simulates a new data set that can be assumed to be acquired by setting many virtual sources on the selected horizon and the associated receivers on the surface. The CTG is generated by isolating all the seismic events passing through the targets after computing the transmitted arrivals from the redatumed source to the related surface receivers. Because the wavepaths corresponding to the CTG are all influenced by the targets below the selected horizon, we can compute frequency-dependent attributes, such as frequency spectrum ratio, to evaluate the attenuation feature of the targets. Numerical tests on synthetic and field data sets validate that the CTG can be used to directly indicate the seismic attenuation.