Slowness (s) is a quantity introduced in
Seismology
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...
which is the
reciprocal
Reciprocal may refer to:
In mathematics
* Multiplicative inverse, in mathematics, the number 1/''x'', which multiplied by ''x'' gives the product 1, also known as a ''reciprocal''
* Reciprocal polynomial, a polynomial obtained from another pol ...
of
velocity
Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...
. 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
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
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
In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from List of types of equilibrium, equilibrium) of one or more quantities. ''Periodic waves'' oscillate repeatedly about an equilibrium ...
is
Therefore, the residual
travel
Travel is the movement of people between distant geographical Location (geography), locations. Travel can be done by Pedestrian, foot, bicycle, automobile, train, boat, bus, airplane, ship or other means, with or without Baggage, luggage, a ...
time is due to departures in slowness experienced by the wave along the raypath.
Sonic well logs
Measurements of interval transit time, designated
, made during
wireline logging
Well logging, also known as borehole logging is the practice of making a detailed record (a ''well log'') of the geologic formations penetrated by a borehole. The log may be based either on visual inspection of samples brought to the surface (' ...
are used to determine sonic velocities of the wallrock in
borehole
A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petr ...
s. 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.
References
External links
*
*
Seismology
Velocity
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