E A R T H Q U A K E G L O S S A R Y
Principle of crosscutting relationships
—the
principle stating that a rock is always younger than
any other rock across which it cuts. Earthquake
faulting illustrates this principle: Faults are always
younger than the rocks they cut.
Principle of superposition—
the principle upon which
all geologic chronology is based stating that in any
sequence of sedimentary layers that has not been
overturned or faulted, each layer is younger than the
one beneath, but older than the one above it.
Principle of uniformitarianism—
the fundamental
principle stating that geologic processes have operated
in essentially the same way throughout geological
time.
Probability—
in mathematics, the ratio of the number
of times something will probably occur to the total
number of possible occurrences. In common usage, an
event is probable, rather than merely possible, if there
is evidence or reason to believe that it will occur.
Qualitative—
having to do with perceived qualities;
subjective. Examples: large, cold.
Quantitative—
having to do with measurable
quantities; objective. Examples: 10 m long, 5º C.
Radiometric dating
—the process of using natural
radioactivity to determine the age of rocks.
Rapid visual screening (RVS)—
a method of
assessing risk that relies on external observation. An
observer who is trained in RVS can derive enough
information from a quick visual assessment to know if
closer examination is necessary.
Rayleigh waves—
surface waves that carry energy
along Earth’s surface by elliptical particle motion,
which appears on the surface as a ripple effect.
Recurrence interval—
the actual or estimated length
of time between two earthquakes in the same location.
Resonance
—an increase in the amplitude (a
measurement of wave size) in a physical system (such
as a building) that occurs when the frequency of an
applied oscillatory form (such as earthquake shaking)
is close to the natural frequency of the system.
Retrofitting
—making changes to a completed
structure to meet needs that were not considered at the
time it was built; in this case, to make it better able to
withstand an earthquake.
Richter magnitude
—the number that expresses the
amount of energy released during an earthquake, as
measured on a seismograph or a network of
seismographs, using the scale developed by Charles
Richter in 1935.
Rigid connections
—connections that do not permit
any motion of the structural elements relative to each
other.
Rotation
—turning from side to side.
Run-up elevation or height—
the highest altitude
above the tide line, in meters, that the water reaches as
it is forced up on land by a tsunami.
S waves
—secondary waves; waves that carry energy
through the Earth in very complex patterns of
transverse (crosswise) waves. These waves move more
slowly than P waves (in which the ground moves
parallel to the direction of the wave). In an earthquake
S waves are usually bigger Ps.
Sag pond—
a small body of water occupying an
enclosed depression formed by fault movement.
Sand boil
—a forcible ejection of sand and water from
saturated soil, caused by strike-slip an earthquake or
heavy flooding.
Saturated
—having absorbed water to the point that all
the spaces between the particles are filled, and no more
water can enter.
Sediment
—material that has been transported by
wind, water, or ice and come to rest in a new location.
Sedimentary deposits—
accumulations of small solid
particles that originated from the weathering of rocks
and that have been transported or deposited by wind,
water, or ice.
Seismicity—
earthquake activity.
Seismic
—of or having to do with earthquakes.
Seismic sea wave
—a tsunami generated by an
undersea earthquake.
Seismic zone
—a region in which earthquakes are
known to occur.
Seismogram—
the record of earthquake ground
motion recorded by a seismograph.
Seismograph
—an instrument that records vibrations
of the Earth, especially earthquakes.
Seismograph station
—a site at which an array of
seismographs is set up and routinely monitored.
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