Scattering attenuation and intrinsic absorption using uniform and depth dependent model-application to full seismogram envelope recorded in Northern Chile

Two seismic wave attenuation factors, scattering attenuation Qs^-1 and intrinsic absorption Qi^-1 are measured using the Multiple Lapse Time Window (MLTW) analysis method for three different frequency bands, 1-2, 2-4, and 4-8 Hz. Data from 54 temporally deployed seismic stations located in northern Chile are used. This method compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model. In the present analysis, the wave energy is assumed to decay with distance in proportion to 1/GSF-exp(- (Qs^-1+Qi^-1)·w r/v), where r, w and v are the propagation distance, angular frequency and S wave velocity, respectively, and GSF is the geometrical spreading factor. When spatial uniformity of Qs^-1, Qi^-1 and v is assumed, i.e. GSF = 4π r², the estimates of the reciprocal of the extinction length, L_e^-1 (= (Qs^-1+Qi^-1)·w/v), are 0.017, 0.012 and 0.010 km^-1, and those of the seismic albedo, Bo (= Qs^-1/(Qs^-1+Qi^-1)), are 0.48, 0.40 and 0.34 for 1-2, 2-4 and 4-8 Hz,respectively, which indicates that scattering attenuation is comparable to or smaller than intrinsic absorption. When we assume a depth dependent velocity structure, we also find that scattering attenuation is comparable to or smaller than intrinsic absorption. However, since the quantitative estimates of scattering attenuation depend on the assumed velocity structure (strength of velocity discontinuity and/or Moho depth), it is important to consider differences in velocity structure models when comparing attenuation estimates.