Spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands – II: Deception Island images

In this work, we present regional maps of the inverse intrinsic quality factor (Qi
−1), the
inverse scattering quality factor (Qs
−1) and total inverse quality factor (Qt
−1) for the volcanic
environment of Deception Island (Antarctica). Our attenuation study is based on diffusion
approximation, which permits us to obtain the attenuation coefficients for every single couple
source-receiver separately. The data set used in this research is derived from an active seismic
experiment using more than 5200 offshore shots (air guns) recorded at 32 onshore seismic
stations and four ocean bottom seismometers. To arrive at a regional distribution of these
values, we used a new mapping technique based on a Gaussian space probability function.
This approach led us to create ‘2-D probabilistic maps’ of values of intrinsic and scattering
seismic attenuation. The 2-D tomographic images confirm the existence of a high attenuation
body below an inner bay of Deception Island. This structure, previously observed in 2-D
and 3-D velocity tomography of the region, is associated with a massive magma reservoir.
Magnetotelluric studies reach a similar interpretation of this strong anomaly. Additionally,
we observed areas with lower attenuation effects that bear correlation with consolidated
structures described in other studies and associated with the crystalline basement of the
area. Our calculations of the transport mean-free path and absorption length for intrinsic
attenuation gave respective values of ≈950 m and 5 km, which are lower than the values
obtained in tectonic regions or volcanic areas such as Tenerife Island. However, as observed in
other volcanic regions, our results indicate that scattering effects dominate strongly over the
intrinsic attenuation.