Absorption and scattering 2-D volcano images from numerically calculated space-weighting functions

Short-period small magnitude seismograms mainly comprise scattered waves in the form ofcoda waves (the tail part of the seismogram, starting after S waves and ending when the noiseprevails), spanning more than 70 per cent of the whole seismogram duration. Correspondingcoda envelopes provide important information about the earth inhomogeneity, which canbe stochastically modeled in terms of distribution of scatterers in a random medium. Insuitable experimental conditions (i.e. high earth heterogeneity), either the two parametersdescribing heterogeneity (scattering coefficient), intrinsic energy dissipation (coefficient ofintrinsic attenuation) or a combination of them (extinction length and seismic albedo) canbe used to image Earth structures. Once a set of such parameter couples has been measuredin a given area and for a number of sources and receivers, imaging their space distributionwith standard methods is straightforward. However, as for finite-frequency and full-waveformtomography, the essential problem for a correct imaging is the determination of the weightingfunction describing the spatial sensitivity of observable data to scattering and absorptionanomalies. Due to the nature of coda waves, the measured parameter couple can be seen asa weighted space average of the real parameters characterizing the rock volumes illuminatedby the scattered waves. This paper uses the Monte Carlo numerical solution of the EnergyTransport Equation to find approximate but realistic 2-D space-weighting functions for codawaves. Separate images for scattering and absorption based on these sensitivity functions arethen compared with those obtained with commonly used sensitivity functions in an applicationto data from an active seismic experiment carried out at Deception Island (Antarctica). Resultsshow that these novel functions are based on a reliable and physically grounded method toimage magnitude and shape of scattering and absorption anomalies. Their extension to 3-Dholds promise to improve our ability to model volcanic structures using coda waves.