Page 97 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

79 Model for critical refraction - depth a critical interfaces. an angle (a). The direct and layers, of e sec-

Models from three horizontal interfaces. V)) results in of the each ray emerges at velocity of the corresponding refracting layer. b) Travel- refracted arrivals indicate the four layer fourth inverses are the from

Interpretation FIGURE 4.6 Increasing velocity with V2 > V3 > > (V, refraction -- from Each refracted indicating the time graph resulting from inverses of the slopes for the velocities. second, third, and 4.6a) (Fig. surface refractions for

&, Vop =Vi/ sin®,4™ Vs B14 ee V./V3 = sin®,, V,/V, = sin®,, V2/V, = sin®,, V3/V, = sin®,, the for angles Earth’s along 4.6b): (Fig. graph Vv Vv, =—l= sin®,, Vv = = Vs sin ®, 5 V; Vi4=—+=V 4 se, velocities apparent &

= Va 8)... = critical the recorded travel-time Vapo V *p3 mw the are layers, respectively.
Sin8y3 Mia Sis NX are the V,,,

Vs / refraction: 6, and velocities on and fourth
Vap = Var * 8,3, observed Vap3, and

sin®y2 critical 8, », respectively. Apparent V9,

V1 / third where slopes where ond, third,
Vap = -

required spreadlengths determined graphs were deeper a of velocity the 4.6). Fig. in V, > V, > V, > deeper and deeper crosses it Rays (Fig. 4.6a). refracting layer than angles higher at emerge corresponding velocities interfaces. shallow with to according interfaces,

Interpretation times (t,), crossover distances (X,,), and (c) deep. Trave]-time moderate; (b) shallow; and text. where interfaces, horizontal (V, above layer of the as horizontal the toward the critically along depth at interface apparent the refractors; associated those higher than successive across bends ray V,/V2 = sin®,, V;/V3 = sin®,,

Refraction Interfaces several that than more horizontally higher-velocity shallow, lower-velocity thus refracted

Seismic Approximate T-axis intercept are (a) that modeling equations presented in of case the greater always and more a along are refractors critically (Fig. 4.6a): refraction: refraction: critical

Chapter4 4.5 for bedrock depths (h) using forward Horizontal Consider is layer bends ray A interfaces, traveling refracted from those deep to Each Law Snell’s critical first second

78 FIGURE Several