Bokelmann, G.H.R., 1995, Azimuth and slowness deviations from the GERESS regional array,
Bulletin of the Seismological Society of America, 85, 5, 1456-1463
For high signal-noise-ratio events, body-wave travel times at GERESS stations are well-fit by a
plane-wave model
corresponding to travel time uncertainties of about 1/100 second. Slownesses obtained in this study are
accurate to about
0.5 s/deg, while azimuth uncertainties are about 2 degrees for regional events and about 5 degrees
for teleseismic nuclear events. For
illustration, we demonstrate performance for Nevada and Tuamotu nuclear tests and for regional events
from Poland.
Unbiased measurement requires array topography (about 200 meters for GERESS) to be taken into account.
If ignored,
these elevation variations give rise to a systematic shift of about 0.6 s/deg to eastern directions,
which is almost independent
of source location. In principle, arrays extending in vertical direction ("3D array") can measure the
vertical slowness and hence local material-velocity . For GERESS we find 5.2 km/sec.
Compared with given accuracies, the regional GERESS array finds statistically significant deviations
of slownesses and azimuths. These may be used to investigate laterally heterogeneous models at regional
scale.
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