This file contains information about the 3-D Vp Imperial Valley model.

Citation:
Patricia Persaud, Yiran Ma, Joann M. Stock, John A. Hole, Gary S. Fuis, Liang Han; Fault zone characteristics and basin complexity in the southern Salton Trough, California. Geology 2016;; 44 (9): 747–750. doi: https://doi.org/10.1130/G38033.1

IV33.dat is the 3D Vp travel time tomography model from Persaud et al. (2016).
The model volume is bounded by the coverage polygon in the paper.
The columns of the file are: x (km) y (km) z (km) vp (km/s), where 
x, y, and z are utm coordinates in km and the columns increase in x.y.z order. 
Grid spacing is 1 km in each spatial dimension. 

1. Number of grid points in x, y, and z. 

nx = 66
ny = 86
nz = 9

nx = 1 is left, nx = 66 is right.
ny = 1 is bottom, ny = 86 is top.
nz = 1 is top, nz = 9 is bottom.

2. Depth, in meters.

Minimum depth = 0 km
Maximum depth = 8 km
depth_interval = 1 km

NOTE: 0 km is ~ sea level and 8 km depth is 8 km below sea level. 

3. Corners in UTM projection.

bottom_left_corner_e = 589 km
bottom_left_corner_n = 3607 km
bottom_right_corner_e = 654 km
bottom_right_corner_n = 3607 km
top_left_corner_e = 589 km
top_left_corner_n = 3692 km 
top_right_corner_e = 654 km
top_right_corner_n = 3692 km

4. Corners in geographic coordinates.

utm zone = 11 S
bottom_left_corner_lon = -116.051578
bottom_left_corner_lat = 32.596922
bottom_right_corner_lon = -115.344866
bottom_right_corner_lat = 32.596922
top_left_corner_lon = -116.051578
top_left_corner_lat = 33.356203
top_right_corner_lon = -115.344866
top_right_corner_lat = 33.356203

5. Additional notes:

(i) Use ray coverage maps from Persaud et al.(2016) to assess reliable areas of the model.
Areas with poor ray coverage are closer to the background 1D model of Kanamori and Hadley (1975).