Br. Julian et al., A geometrical error in some computer programs based on the Aki-Christofferson-Husebye (ACH) method of teleseismic tomography, B SEIS S AM, 90(6), 2000, pp. 1554-1558
Some computer programs based on the Aki-Christofferson-Husebye (ACH) method
of teleseismic tomography contain an error caused by identifying local gri
d directions with azimuths on the spherical Earth. This error, which is mos
t severe in high latitudes, introduces systematic errors into computed ray
paths and distorts inferred Earth models. It is best dealt with by explicit
ly correcting for the difference between true and grid directions. Methods
for computing these directions are presented in this article and are likely
to be useful in many other kinds of regional geophysical studies that use
Cartesian coordinates and flat-earth approximations.