Snell’s Law

Northern Sh Shot-gather

Seismic Data

Seismic Data

Southern P- Shot-gather

criticalangle V1,rho1

V2,rho2

P`

P`P’

At critical angle of incidence,angle of refraction = 90 degrees=angle of reflection

Pre- and Post-critical Raysx

z V1

V2 V2> V1

Pre-critical reflections Head wavePost-critical reflections

Direct wave

11

tan V

21

tanV

Critical distance

One-layer Refracted Head Wave

x

z V1

V2V2> V1

c

Critical distance=Xc

cr1 r1 r3

r2

1x 2

x3x

Xc =? Tc=?

One-layer Refracted Head Wave

x

z V1

V2V2> V1

c

Critical distance=Xc

cr1 r1 r3

r2

1x 2

x3x

Xc =? Tc=?

1 2 12

cX x x x

02 tan

c cX z

z0

1 1 1

1 1 1

2c

r r rTV V V

0

1

2cosc

c

zTV

(9)

One-layer Refracted Head Wave

x

z V1

V2V2> V1

c

Critical distance=Xc

cr1 r1 r3

r2

1x 2

x3x

Xc =? Tc=?

z0

Xc +

2 02

2 1

( ) 2cosc

c

x zT x xV V

2x

(10)