Slowness (seismology)

Slowness (s) is a quantity introduced in Seismology which is the reciprocal of velocity. Thus travel time of a wave is the distance that the wave travels times the slowness of the medium ( in seismology, it refers to different layers of Earth exhibiting different densities) Thus,

Slowness = 1/Velocity

If we divide the path followed by the ray into N segments numbered i = 1, 2 .. N the total travel time of the wave is

$\Gamma =\sum _{i=1}^{N}s_{i}\Delta x_{i}$

Therefore, the residual travel time is due to departures in slowness experienced by the wave along the raypath.

Sonic well logs

Measurements of interval transit time, designated ${\Delta }t$ , made during wireline logging are used to determine sonic velocities of the wallrock in boreholes. The tool used has sources and receivers that are in contact with the wellbore and it measures the delay between the source being triggered and the signal being received. The measurements are normally in the units of microseconds per foot and are recorded on the well log.[1]

References

Glover, Paul. "16. The Sonic or Acoustic Log" (PDF). Petrophysics MSc Course Notes. Retrieved 11 December 2015.

External links

Ram, A.; Yadav, L. (1984), "Structural corrections for slowness and azimuth of seismic signals arriving at Gauribidanur array", Bulletin of the Seismological Society of America, Seismological Society of America, 74 (1): 97–105, Bibcode:1984BuSSA..74...97R, doi:10.1785/BSSA0740010097
Stein, S.; Wysession, M. (1991). An Introduction to Seismology, Earthquakes, and Earth Structure. Wiley. ISBN 978-0-86542-078-6.

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[1] Glover, Paul. "16. The Sonic or Acoustic Log" (PDF). Petrophysics MSc Course Notes. Retrieved 11 December 2015.