GLOSSARIES - Geotechnical Earthquake Engineering - page 517

Terrace A relatively level step constructed in the face of a graded slope surface for drainage con-
trol and maintenance purposes.
Underpinning Piles or other types of foundations built to provide new support for an existing foun-
dation. Underpinning is often used as a remedial measure.
Vibrodensification The densification or compaction of cohesionless soils by imparting vibrations
into the soil mass so as to rearrange soil particles, resulting in less voids in the overall mass.
Walls
Bearing Wall Any metal or wood stud wall that supports more than 100 lb per linear foot of
superimposed load. Any masonry or concrete wall that supports more than 200 lb per linear foot of
superimposed load or is more than one story ( Uniform Building Code 1997).
Cutoff Wall The construction of tight sheeting or a barrier of impervious material extending
downward to an essentially impervious lower boundary to intercept and block the path of groundwa-
ter seepage. Cutoff walls are often used in dam construction.
Retaining Wall A wall designed to resist the lateral displacement of soil or other materials.
Water-Cementitious Materials Ratio Similar to the water-cement ratio, the ratio of the mass
of water (exclusive of that part absorbed by the aggregates) to the mass of cementitious materials in
the concrete mix. Commonly used cementitious materials for the concrete mix include Portland
cement, fly ash, pozzolan, slag, and silica fume.
Water-Cement Ratio For concrete mix design, the ratio of the mass of water (exclusive of that
part absorbed by the aggregates) to the mass of cement.
Well Point During the pumping of groundwater, the perforated end section of a well pipe where the
groundwater is drawn into the pipe.
Windrow A string of large rock buried within engineered fill in accordance with guidelines set forth
by the geotechnical engineer or governing agency requirements.
Workability of Concrete The ability to manipulate a freshly mixed quantity of concrete with a
minimum loss of homogeneity.

GLOSSARY 5 EARTHQUAKE TERMINOLOGY

Active Fault See Fault.
Aftershock An earthquake which follows a larger earthquake or main shock and originates in or
near the rupture zone of the larger earthquake. Generally, major earthquakes are followed by a large
number of aftershocks, usually decreasing in frequency with time.
Amplitude The maximum height of a wave crest or depth of a trough.
Anticline Layers of rock that have been folded in a generally convex upward direction. The core of
an anticline contains the older rocks.
Array An arrangement of seismometers or geophones that feed data into a central receiver.
Arrival The appearance of seismic energy on a seismic record.
Arrival Time The time at which a particular wave phase arrives at a detector.
Aseismic A term that indicates the event is not due to an earthquake. An example is an aseismic
zone, which indicates an area that has no record of earthquake activity.
Asthenosphere The layer of shell of the earth below the lithosphere. Magma can be generated
within the asthenosphere.
Attenuation Relationship A relationship that is used to estimate the peak horizontal ground
acceleration at a specified distance from the earthquake. Numerous attenuation relationships have been