dt/d delta Measurement of Short Period P Waves in the Upper Mantle for the Western North America using LASA
MASSACHUSETTS INST OF TECH CAMBRIDGE
Pagination or Media Count:
Seismic ray parameter dtd delta has been measured in the distance range delta 8-344 utilizing LASA. An upper mantle velocity structure for P waves applicable to the Western Part of North America has been derived from these data. Measurement of dtd delta was accomplished by calculating with a least squares procedure the dtd delta from the measured arrival time at each sub-array or by forming beams with LASA from which dtd delta was picked from the beams that gave the maximum amplitude. The velocity models were calculated by a Monte Carlo technique and show a low velocity region centered at a depth of 120 km and two zones of rapid velocity increase at 350 km and 650 km where the velocity changes from 8.7 to 9.6 kmsec and 10.2 to 10.9 kmsec, respectively. Our dtd delta data supports the accumulating evidence that dtdA is azimuthally dependent at LASA. Also, the data suggests that this azimuthal dependence is a result of structural anisotropy under LASA.
- Statistics and Probability