This glossary of earthquake and landslide terms was prepared
by the law firm of Michael
T Chulak & Associates for non-attorneys to assist them in
understanding earthquakes, landslides and mudslides. This glossary
of earthquake and landslide terms is general information only
and is not intended to be legal advice. If you need legal advice,
you should consult with an attorney licensed in your state.
is an earthquake that occurs from hours to months after
the larger earthquake or mainshock has occurred. Aftershocks
occur in the same general area as the mainshock and are
believed to be the result of minor readjustments of stress
within the fault zone. Aftershocks decrease in frequency
and strength over time. Generally, the larger the mainshock,
the larger the aftershocks.
Angle of Rest
also known as the angle of repose. This is the angle
at which material (such as soil) will remain stable.
is a massive fall of ice and snow sometimes caused by
is a vibration from an earthquake that travels deep underground.
refers to the slow, usually continuous movement that
takes place along many faults. Creep does not cause shaking.
is the shaking of the earth caused by a sudden movement
of rock beneath the surface. Earthquakes cause seismic
waves that travel from the point of rupture. These waves
shake the earth as they travel.
is the point on the Earth’s surface directly above the
focus or hypocenter of the earthquake.
is a break in the Earth along which movement occurs during
an earthquake. It is the sudden movement along a fault
that causes an earthquake. Slow movement results in seismic
creep. There are three types of faults- thrust, normal
is the Federal Emergency Management Agency. It is the
agency responsible for identifying and mitigating natural
and man-made hazards. FEMA also administers the National
Flood Insurance Program.
or Hypocenter is the point within the Earth from which
the earthquake originates.
is a small tremor that often precedes the main shock
from a matter of a few seconds to weeks. It originates
at or near the rupture zone of the primary earthquake.
study rocks and geologic features.
are civil engineers. Geotechnical Engineers also assess
the risk to people and property from natural hazards such
as landslides, sinkholes, earthquakes and soil liquefaction.
iis the same as the focus.
is the measure of the shaking at a particular point.
The intensity at any point depends upon both the strength
of the earthquake (magnitude) and the distance from the
epicenter. Intensity refers to the effect or severity
of the earthquake.
is a downward movement of soil, rocks and possibly mud,
plant material, structures and roads. When the soil liquefies,
it becomes a mudslide or mudflow. Landslides can be very
violent moving more than twenty miles per hour or may
move as slowly as two to three inches in a year. Landslides
can be triggered by earthquakes or heavy rains or may
be caused by man.
is the process that takes place when large earthquakes
shake sandy soil until it starts to resemble liquid, allowing
sand to “boil up” to the surface, structures to sink,
and/or slopes to fail.
refers to the quantity of energy released by an earthquake
as compared to intensity which describes the effect at
a particular point. Several earthquake magnitude scales
exist including the Richter Magnitude Scale.
is the largest in a series of earthquake shocks. The
mainshock is usually preceded by one or more foreshocks
and followed by one or more aftershocks.
is used to measure the intensity of earthquakes ranging
from a scale of one to twelve. It is based upon the effects
on people and buildings. A level of twelve equates to
is similar to a landslide except that it occurs when
a slope is so heavily saturated with water that it rushes
down hill in the form of a muddy river spreading out at
the base of the slope.
are giant slabs of underground rocks that are sometimes
larger than continents.
is an insurance adjuster who represents an insured on
a fee basis. A public adjuster is not licensed to practice
refers to strengthing existing structures to improve
Richter Magnitude Scale
was developed in 1935 by Charles Richter as a mathematical
device to compare the sizes of earthquakes. The magnitude
of an earthquake is determined by an instrument called
a seismograph. On the Richter Scale, magnitude is measured
in whole numbers and decimals. Because of the logarithmic
basis of the scale, each whole number increase in magnitude
represents a ten fold increase in magnitude. For example,
a magnitude 6 is ten times greater than a magnitude 5
earthquake. The scale is measured from one to ten. The
Richter Scale is also known as the local scale.
Ring of Fire
is the area around the Pacific Ocean where there is a
high level of seismic activity taking place. The western
coast of the United States is included in this area.
is the area of fault movement. It may extend for hundreds
of miles in length and may or may not extend to the surface
of the Earth.
is the Small Business Administration which is a federal
agency that provides various types of loans for businesses,
home-owners and renters in the event of disaster.
means having to do with earthquakes.
are the vibrations from earthquakes that travel through
the Earth. They are recorded and measured on instruments
called seismographs. There are three types of waves: P
(fastest), S (slower) and surface waves (slowest).
is a graph showing ground motion over time.
is a scientific instrument used to detect and measure
is a scientist who studies earthquake causes and results.
is a sudden subsidence of land, often relatively flat
areas, underlain by limestone or similar materials.
refers to the intensity of two forces working against
is generally a vertical fault along which the two sides
move horizontally. The best known example is the large
San Andreas Fault in California.is generally a vertical
fault along which the two sides move horizontally. The
best known example is the large San Andreas Fault in California.
is the vertical fall of soil caused by lack of adequate
is a vibration from an earthquake that travels at ground
are the shaking of the Earth caused by earthquakes.
is one or more waves caused by the rapid displacement
of water by major earthquakes usually exceeding a magnitude
of 7.5, or a significant under water landslide. In the
open ocean they may travel at speeds exceeding 300 kilometers
per hour. They are capable of crossing entire oceans and
can exceed 30 meters in height when they reach the shoreline.