Ccor.f is a subroutine which calculates corrections to travel times using the model CRUST5.1 compiled by Mooney et al. (JGR, v. 103 , 727, 1998). The corrections are calculated relative to a reference 1-D earth model which you must supply. This routine calls 2 other subroutines supplied by Mooney. Ccor.f along with all of the appropriate subroutines can be found in /scr/024/antolik/tt_cor/mooney.

To use this routine, you must supply the following:

1. Reference model in the form of layers (Vp,Vs,Qmu,Qkappa, etc..) This is passed to the routine through the common block /MODEL/. The arrays are set so that the maximum number of layers is 600. The common block /MODEL/ also includes layer boundary number of the moho (nmoho), the inner core (nic), the CMB (noc), and the 670-km discontinuity (n670) numbered from the center of the Earth outward. Only nmoho is used within the program. The values of radius at each of the layer boundaries are passed through the array 'rad'.
2. Ray parameter of input phase (calculated using the reference model). This is the argument 'pray'.
3. The phase name and location of the receiver (or source). These are supplied through the argument list.

The travel time in each layer of the models is calculated by first finding the incidence angle of the ray on the boundary:

where p is the ray parameter and v_k is the velocity within the k_th layer. It is then straightforward to compute the path length and travel time through each layer. The algorithm determines the total path travel time within CRUST5.1 and the reference model and passes both of these values back to the calling program. Ccor.f calculates these values for one leg of the ray only (source or receiver). Calculation of the receiver-side correction is done by entering a value of 0.0 as the source depth.

If CRUST5.1 contains a water layer at the location in question, it is removed and replaced by a layer of equivalent thickness and having the same velocities as the top of the oceanic crust.

The program assumes a P_n velocity of 8.0 km/s and an S_n velocity of 4.4 km/s for CRUST5.1.

The travel times are computed up to sea-level (Elevation information in CRUST5.1 was removed). This allows users to deal with station elevation corrections as they see fit.

Ccor.f currently works for all direct, depth, and core phases. Surface reflected phases such as PP, PS, etc.., have not yet been implemented.

Send any questions about the program to Mike Antolik.