Results of receiver function stacking for each of the circles.
The columns are:
clon - longitude of the circle's center
clat - latitude of the circle's center
d410 - depth of the d410
sig4 - standard deviation of the depth of the d410
d660 - depth of the d660
sig6 - standard deviation of the depth of the d660
MTZ - Mantle Transition Zone thickness
sigm - standard deviation of MTZ thickness
a4 - stacking amplitude of the d410
a6 - stacking amplitude of the d660
NRFs - Number of receiver functions in the circle
Note that a value of zero is given to the depth if the Pds arrival is
not well-defined.