SUMMARY

Sets stack velocity model parameters for computing dynamic delays.

SYNTAX

[V]ELOCITY[M]ODEL n options

where options are one or more of the following:

ON|OFF
REFRACTEDWAVE|NORMALMOVEOUT
FLIP
VAPP v|CALCULATE
T0VM v|CALCULATE
DVM v1 [v2]
TVM v1 [v2]
VAPPI v
T0VMI v

INPUT

n: Set velocity model number. This is either "1" or "2". The use of each velocity model is described below.

ON|OFF: Turn velocity model option on or off. When this option is on the model is applied. When off it is ignored.

REFRACTEDWAVE: Turn velocity model option on and change to the "refracted wave" model.

NORMALMOVEOUT: Turn velocity model option on and change to the "normal moveout" model.

FLIP: Interchange the properties of the two velocity models.

VAPP v: Set the apparent velocity to v.

VAPP CALCULATE: Have SAC calculate the apparent velocity.

T0VM v: Set the time axis intercept to v.

T0VM CALCULATE: Have SAC calculate the time axis intercept.

DVM v1 [v2]: Define one or two reference distances.

TVM v1 [v2]: Define one or two reference times.

VAPPI v: Set the apparent velocity increment to v. The apparent velocity is incremented by this ammount each time the INCREMENTSTACK command is executed.

T0VMI v: Set the time axis intercept increment to v. The time axis intercept is incremented by this ammount each time the INCREMENTSTACK command is executed.

n:	Set velocity model number. This is either "1" or "2". The use of each velocity model is described below.
ON\|OFF:	Turn velocity model option on or off. When this option is on the model is applied. When off it is ignored.
REFRACTEDWAVE:	Turn velocity model option on and change to the "refracted wave" model.
NORMALMOVEOUT:	Turn velocity model option on and change to the "normal moveout" model.
FLIP:	Interchange the properties of the two velocity models.
VAPP v:	Set the apparent velocity to v.
VAPP CALCULATE:	Have SAC calculate the apparent velocity.
T0VM v:	Set the time axis intercept to v.
T0VM CALCULATE:	Have SAC calculate the time axis intercept.
DVM v1 [v2]:	Define one or two reference distances.
TVM v1 [v2]:	Define one or two reference times.
VAPPI v:	Set the apparent velocity increment to v. The apparent velocity is incremented by this ammount each time the INCREMENTSTACK command is executed.
T0VMI v:	Set the time axis intercept increment to v. The time axis intercept is incremented by this ammount each time the INCREMENTSTACK command is executed.

DEFAULT VALUES

VELOCITYMODEL 1 OFF
VELOCITYMODEL 2 OFF

DESCRIPTION

The first velocity model is used in calculating dynamic station delays for a particular phase.

It is applied when doing a stack summation ( SUMSTACK), a stack plot ( PLOTSTACK), or a record section plot ( PLOTRECORDSECTION.) The second velocity model is used in the record section plot to show delays associated with a second phase. The parameters associated with the two velocity models can be easily flipped.

There are two different types of velocity models ("refracted wave" and "normal moveout") that can be applied. They are defined by the following equations:
TDELAY = TVM(1) - ( T0VM + DIST / VAPP )
TDELAY = TVM(1) - SQRT ( T0VM**2 + ( DIST / VAPP )**2 )
There are several ways in which these velocity model delays can be calculated:

Enter values for VAPP, T0VM, and TVM(1) directly.

Enter values for DVM(1), TVM(1), and either VAPP or T0VM. SAC will calculate the missing variable such that TDELAY will be zero at the distance given by DVM(1).

Enter values for DVM(1), TVM(1), DVM(2), and TVM(2). SAC will calculate both VAPP and T0VM such that TDELAY will be zero at the distance given by DVM(1).

EXAMPLES

To set the first stack velocity model the refracted wave model with an apparent velocity of 6.5 km/sec and to have SAC calculate T0VM such that the delay at 200 km will be zero:
SAC> VELOCITYMODEL 1 REFRACTEDWAVE VAPP 6.5 T0VM CALCULATE DVM 200 TVM 35

SEE COMMANDS

SUMSTACK, PLOTSTACK, PLOTRECORDSECTION