E A R T H Q U A K E G L O S S A R Y
Seismology
—the scientific study of earthquakes.
Shaking
—rapid horizontal vibration of the base of the
model, simulating an earthquake. In an actual
earthquake, of course, shaking occurs in many
directions.
Shear force
—force that acts horizontally (laterally) on
a wall. These forces can be caused by earthquakes and
by wind, among other things. Different parts of a wall
experience different shear forces.
Shear walls—
walls added to a structure to carry
horizontal (shear) forces. These are usually solid
elements, and are not necessarily designed to carry the
structure’s vertical load.
Sill plate
—the structural member at the base of a
wood frame building that joins the building to its
reinforced concrete foundation.
Slump—
a type of landslide in which a block of rock
or soil moves along a curved surface and rotates.
Soft stories—
stories in a building, usually lower
stories with many openings, that are poorly supported
or braced, and hence vulnerable to collapse.
Stick-slip movement
—a jerky, sliding movement
along a surface. It occurs when friction between the
two sides of a fault keeps them from sliding smoothly,
so that stress is built up over time and then suddenly
released.
Strata (s.
stratum
)
—layers of rock or other materials
formed at different periods in geologic time.
Strike-slip faulting
—fault movement in which the
fault is horizontal.
Structural elements or structural features
—a
general term for all the essential, non-decorative parts
of a building that contribute structural strength. These
include the walls, vertical column supports, horizontal
beams, connectors, and braces.
Studs
—upright pieces in the outer or inner walls of a
building to which panels, siding, laths, etc. are nailed
or bolted.
Subduction
—the process in which one lithospheric
plate is forced down under another plate and drawn
back into the Earth’s mantle.
Surface waves
—waves that move over the Earth at its
surface. Rayleigh waves and Love waves are surface
waves.
Topography (
adj
.
topographic
)
—the
shape of the
land; the contours and the arrangement of surface
features that characterize a region.
Torsion—
twisting or turning. A building must be
resistant to extreme torsion to resist earthquake
damage.
Transverse waves
—waves that vibrate particles in a
direction perpendicular to the wave’s direction of
motion (S waves).
Triangulation
—using data from three or more known
points to locate an unknown point, in this case, the
epicenter of an earthquake.
Tsunami
—a potentially destructive ocean wave
created by an earthquake or other large-scale
disturbance of the ocean floor; a seismic sea wave.
This Japanese word has the same form in both the
singular and the plural.
Unconsolidated
—loosely arranged, not cemented
together, so particles separate easily.
Unreinforced masonry
—brick, stone, or adobe walls
without any steel reinforcing rods or other type of
reinforcement. Buildings of this type were probably
built before 1940.
Variable
—in a scientific experiment, the one element
that is altered to test the effect on the rest of the
system.
Veneer
—an outside wall facing of brick, stone, or
other facing materials that provides a decorative
surface but is not load-bearing.
Vertical load
—the effect of vertical force (gravity)
acting on the elements of a structure.
Wave height
—the vertical distance from a wave’s
crest to its trough. (This measurement will be twice the
amplitude measured for the same wave.)
Wave crest
—the highest point a wave reaches. The
lowest point is called its
trough.
Wavelength
—the horizontal distance between two
successive crests, often measured in meters.
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