A Novel Approach for the Estimation of Seismic Q and Coda Q

The ground motions observed at the surface due to artificial source (exploration seismology) or natural source (earthquake seismology) are affected by source characteristics, medium properties and site conditions. The medium properties are related to the attenuation of seismic waves propagating between source and receiver. The attenuation properties of a medium affect the amplitudes of ground motions at various distances from the source. Subsurface factors attributing to the seismic wave attenuation are geometrical spreading, absorption, inter-bed multiples generated by thin layering, diffractions and the focusing or defocusing effects of the reflector curvature or velocity. Among these subsurface factors, absorption reveals geological information, which includes attenuation of both intrinsic and scattering effects. Seismic wave attenuation plays a pivotal role in exploration seismology as well as in earthquake seismology. In exploration, it helps in improving the seismic resolution for reliable interpretation of hydrocarbon prospects and can be used as an attribute for delineation of the reservoirs. In earthquake seismology, it correlates with regional heterogeneities such as major folds, faults or near-surface complexities and helps in categorizing the scale of tectonic activity in the region.

Seismic waves undergo attenuation and dispersion attributing to the frictional losses or the scattering while passing through the dissipative earth. The frictional losses are often termed as intrinsic attenuation, which occurs due to the relative movement of grains or fluids in the rock matrix. The intrinsic properties of the medium such as grain type, architecture, porosity, fluid type, viscosity, permeability, saturation and pressure are usually accountable for these losses in sedimentary rocks. Scattering attenuation is because of random heterogeneities in the near surface or weathered basalts and by the layering effects such as stratigraphic filtering. Both intrinsic and scattering losses eventually lead to phase distortion, degradation of seismic resolution and poor imaging below absorptive zones.