Page 87 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

the is
have vertical; to travel fronts to velocity
arrivals is a
69 velocities than direct fronts are front next velocity of the wave
- A
for front strikes velocity travel Refracted the Refracted the surface at an angle equal
Techniques Apparent velocity. wavefront refracted wave. wave X,. b) Travel- for critically refracted arrival. to X;. to 3.34 higher apparent wave Direct it takes a wave receiver to true (V,). critical angle (6,); the apparent V3. =

Seismic raypaths and then at inverse of the the wave appeared from X, FIGURE arrivals. the time from one function of the material strike V,/sin®,

Source 3.33 FIGURE a) Selected an emerging, critically time AT elapses as the the receiver at X, graph The slope is the that (V,,) along the surface

Controlled time AX lay é AXsin®, AX VS AX sin®, sind,

To Do 2 ~ as es AY = = Ve a Vi
Elap. sed Time = AT AX Fronts 5 meaning

7; < ween e renee Wave Refracted MA, wy es AY/AX, =

a Direct wey : : sin@, But: that: so
i Wavefronts j ‘Sy

‘ j
‘

and wave) divided a with veloc- the hori- velocity an velocity
from by travel at
up the interface is, a seismic line, 3.32): travel apparent divided shallow ground apparent the (AY).
back straight (Fig. to that the velocity (V,) takes a distance
and to (that appears The receivers, fronts the from it (AT)
layer. to down along a material 3.33). wave to equal than V,. The The true time travel

of surficial : (%) xX? Hie Ve path, down vertically location): which seismic energy traversed of the (V,) however, (Fig. of receivers spaced closely vertical velocity wave emerge faster /V, 3.32 FIGURE the depends on seismic energy to

thickness angle critical \ iF 0 V-shaped (time go to shot the 2h bry l at (AY) velocity AY V.== AT a surface, Earth’s array two receivers: two _ AX Vv, AT "6 has source a at refracted appears AX = AT wit AY/V

oD " T, interface to up distance true that is: Vip VY,
ll " along between the geophones
2 Velocity the at surface wave
a om intercept back actual speed to critically rate
time (AT), gives emerging horizontal (AX) (AT) a a a at
Seismic Waves travel = T;, reflecting T-axis = ty straight Apparent and to the material. The a time “ wave a across distance the time travel from arrival striking 3.34), from fronts passing geophones refracted critically

Chapter3 Reflected Wave: Velocity True velocity refers travels through elapsed the by seismic A velocity certain is (V,,) ity difference in direct A (Fig. zontally (V,). Wave angle, such a for

68 True

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