Article,
Characterization of regional and local scattering effects from small-aperture seismic array recordings
Journal of Seismology, 9 (2): 137--149 (Apr 15, 2005)
DOI: 10.1007/s10950-005-8234-1
Abstract
In 1998, four small-aperture arrays separated by 20 km have been deployed
in the southern French Alps in order to record the natural seismicity
during two consecutive months. One of the main objectives of this
experiment was to characterize the heterogeneities that influence
the wavefield propagation, by analysis of the coda characteristics
recorded by each of the seismic arrays.The time-azimuth-velocity
characteristics of the coda phases have been obtained using a high-resolution
wavenumber decomposition method.A statistical analysis, using the
coda characteristics of the whole data set (20 regional earthquakes)
recorded by the four arrays has been performed and lead to the calculation
of the density of scattered energy within the medium. Three regional
heterogeneous areas (> 10 km) have been characterized, and are located
in the N-NE, W and S directions from the four arrays. Scattered energy
is also located at local distances (< 10 km) from the four arrays.
The comparison of the waveforms recorded (i) with one of the array,
for different groups of earthquakes, and (ii) with the four arrays,
for one group of earthquakes, show that the geometrical configuration
of the source-scattering area-recording site system can strongly
influence the energetic distributions related to the secondary phases
of the seismograms.In particular cases, we experimentally show that
the interactions of the direct wavefield with the heterogeneous structures
of the medium can be sufficiently energetic to induce secondary scattered
phases that dominate the seismic motions recorded at a given site.
In such case, these effects should be taken into account for the
quantification of the expected ground motion recorded during an earthquake.
