E A R T H Q U A K E G L O S S A R Y
Load path
—the path a load or force takes through the
structural elements of a building.
Loess
—an unstratified, windblown mixture of clay,
sand, and organic matter, usually crumbly and buff or
yellow-brown in color.
Longitude
—the location of a point east or west of the
prime meridian, expressed in degrees and minutes.
Longitude is shown on a map or globe as north-south
lines left and right of the prime meridian, which passes
through Greenwich, England.
Longitudinal waves
—p-waves. This term is used to
emphasize that p-waves move particles back and forth
in the same line as the direction of the wave.
Love waves
—surface waves that move in a back and
forth horizontal motion.
Magnitude
—a number that characterizes the size of
an earthquake by recording ground shaking on a
seismograph and correcting for the distance to the
epicenter of the earthquake. Magnitude is expressed in
Arabic numbers.
Masonry
—stone, brick, or concrete building
materials.
Masonry veneer
—a masonry (stone or brick) facing
laid against a wall and not structurally bonded to the
wall.
Mass movement
—the movement of surface material
caused by gravity.
Meteorology
—the study of Earth’s atmosphere.
Modified Mercalli scale of 1931
—a qualitative scale
of earthquake effects that assigns an intensity number
to the ground shaking for any specific location on the
basis of observed effects. Mercalli intensity is
expressed in Roman numerals.
Natural hazard—
any of the range of natural Earth
processes that can cause injury or loss of life to human
beings and damage or destroy human-made structures.
Nonstructural feature
—an element of a building that
is not essential to its structural design and does not
contribute structural strength. Examples are windows,
cornices, and parapets.
Oscillation or vibration
—the repeating motion of a
wave or a material—one back and forth movement.
Earthquakes cause seismic waves that produce
oscillations, or vibrations, in materials with many
different frequencies. Every object has a natural rate of
vibration that scientists call its
natural
frequency.
The
natural frequency of a building depends on its physical
characteristics, including the design and the building
materials.
P waves
—primary waves, so called because they
travel faster than S waves, or secondary waves and
arrive at the station first. These waves carry energy
through the Earth as longitudinal waves, moving
particles in the same line as the direction of the wave.
Paleomagnetism
—the natural magnetic traces that
reveal the intensity and direction of Earth’s magnetic
field in the geologic past.
Paleoseismology
—the study of ancient earthquakes.
Parapet
—part of a wall which is entirely above the
roof.
Path, or Load path
—the direction in which energy is
distributed throughout a structure. In most structures, it
should be directed toward the ground.
Peat
—a deposit of semicarbonized plant remains in a
water-saturated environment. Peat is an early stage in
the development of coal.
Period
—the time between two successive wave crests.
Pioneer
—a person who moves into new and uncharted
territory.
Plate tectonics
—the theory that Earth’s crust and
upper mantle (the lithosphere) are broken into a
number of more or less rigid, but constantly moving,
segments, or plates.
Portico
—a porch or covered walk consisting of a roof
supported by columns
Prediction
—a statement that something is likely to
happen based on past experience. A prediction is
usually only as reliable as its source.
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