C. Dorbath et al., TOMOGRAPHY OF THE ANDEAN CRUST AND MANTLE AT 20-DEGREES-S - FIRST RESULTS OF THE LITHOSCOPE EXPERIMENT, Physics of the earth and planetary interiors, 97(1-4), 1996, pp. 133-144
In 1994, a temporary network of 41 short-period seismic stations opera
ted for 6 months along an east-west profile in Northern Chile and Boli
via. The profile crossed the entire Andean chain at a latitude of 20 d
egrees S. We present the results of the teleseismic tomography of the
crust and mantle along an east-west vertical cross-section beneath the
profile. The most striking feature of the tomographic image is the id
entification of the subducted Nazca plate. It appears as a zone of hig
h velocities which is continuous over the aseismic part of the slab do
wn to the 660km discontinuity. In the continental lithosphere, strong
lateral P-wave velocity variations are found in the crust whereas the
upper mantle shows only small velocity variations, Major lateral chang
es in crustal velocity coincide with the limits of the main structural
units of the Andean range. The distribution of velocity anomalies in
the crustal layer matches the lateral changes in crustal thickness and
average velocity deduced from refraction surveys. A comparison with a
previous tomographic experiment in Northern Bolivia confirms that the
northern and southern segments of the Bolivian orocline have differen
t lithospheric structures.