Iterative tomographyc analysis based on automatic refined picking

The ever-growing size of data sets for active and passive seismic imaging makes the
availability of automatic procedures for rapid analysis more and more valuable. Such
procedures are especially important for time-critical applications like emergency decisions
or re-orienting of ongoing seismic surveys. In this paper a new, iterative scheme
for 3D traveltime tomography is presented. The technique, based on a tool originally
developed for earthquake data, uses cross-correlation to examine waveform similarity
and to adjust arrival times on seismic sections. A preliminary set of reference arrival
times is first corrected by the cross-correlation lag and then used to build an initial
3D tomographic velocity model through a standard inversion code; traveltimes calculated
from this model are then taken as new reference arrivals and the process of pick
adjustment is repeated. The result is a tomographic image, upgraded and refined at
each iteration of the procedure. The test performed on the waveform data set recorded
during the 2001 SERAPIS active seismic survey in the gulfs of Naples and Pozzuoli
(Southern Italy) shows that the 3D iterative tomography scheme produces a velocity
image of the structure of the Campi Flegrei caldera which is consistent with the results
from previous studies, employing just a fraction of the time needed by a human analyst
to identify first breaks.We believe that this technique can be effectively employed
for rapid analysis of large data-sets within time-critical or time-dependent tasks and
for automatic 4D tomographic investigations.

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