[CIG-SEISMO] SW4 - question on p-file

[Avinash Nayak]

Hi,

I have a few questions on p-files in the wave propagation software SW4
and I will be grateful for some help on this.

What exactly is the frame of reference for the cartesian coordinates
(x,y) in the input p-file ? Is it x-y with respect to the origin (0,0
or lat,lon) of the grid provided in the grid command ?

If I understand correctly (which may be wrong), the way the input
cartesian and geographic lattices are described in the p-file format,
they need to be uniformly spaced (in each direction separately) and
the material grid on p-file must have zero azimuth (nested double loop
on page 89 in the manual) even though it specifically takes latitude
and longitude or x-y of each horizontal grid point.

In the beginning of the input p-file,

Nlat (integer) Latmin [deg] (real) Latmax [deg] (real)

But then it also requires

Lat(i,j) Long(i,j) number_of_depth_points for each profile.

I have a velocity model which is a uniform grid with zero azimuth in
UTM WGS84 coordinates (meters). If I transform it to geographic
coordinates, it is not uniform or zero-azimuth anymore. I thought of
using it as a cartesian input, but I want my computation grid to have
a non-zero azimuth as that reduces the size of my computation domain.
Then, with respect to the x-y frame of the computation grid, my
velocity model grid has non-zero azimuth and now I am not sure how to
input it as a p-file.

I will really appreciate your help on this.
Thanks.

Sincerely yours,
Avinash