Page 74 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

57
Techniques
Seismic
Source
Controlled
wave for fronts traveled distance the by divided (AT) time elapsed the is line the of slope The (AX): time that during increasing distance graph. AT = aX Slope according plotted to the source deriva- first the taking by determined be also can (X) distance given a at slope The (T). time 3.18a): (Fig. curve time travel the on point that at tive (3) dT AX lim =
Initial R waves, propagating across from each receiver. The elapsed time after the travel receiver refrac- Earth. from surface
a) at from the source. b) Travel-time (X) the is plotted each in
3.17 receivers The seismic traces are to the distance are to downward the time receiver the
FIGURE P,S,and several source is fired receivers source within travel curve: the to along
Traces of Receivers several from as to arrivals, travel-time the receiver, measured
... the increasing depth the source

Seismic for each the from (X) distance plotted relates often R-wave the by from travel the arrival. R

o Jt traces or to or
é 6 6 f=, \ Dispersion: Ranges commonly T to source PS,
x 5 (X) => 5 ——|____| seismic horizontal is because S-wave, linear, expressed the wave the the of
Waves 4 _ ff graph the (T) studies, P-wave, is for from velocity

Seismic R 'eCe, ive rs 3 tH Source 4 travel-time to time reflection initial receiver time total X= distance seismic

3 fi P From 3 a On according 3.17). Travel and the a to = T = V
Chapter Distance 2 - side, by (Fig. tion of each source where:

56 1

b (D) eu joAeLL —=