Glossary

Vibrations in the earth produced during earthquakes.

Seismic or earthquake activity.

Clay soil that experiences a particularly large loss of strength when disturbed. Deposits of sensitive clay are subject to failure during earthquake ground shaking.

The internal resistance that tends to prevent adjacent parts of a solid from “shearing” or sliding past one another parallel to the plane of contact. It is measured by the maximum shear stress that can be sustained without failure.

A  stress causing adjacent parts of a solid to slide past one another parallel to the plane of contact.

A general term referring to any type of natural ground movement on a sloping surface (see landslide).

A slope failure that slides along a concave rupture surface. Generally slumps do not move very far from the source area.

A rapid downslope movement of a mass of snow, ice, and debris.

Measurement for approximate horizontal force experienced in a model earthquake. Measurements are specific to the frequency of shaking found to affect buildings during and earthquake. A 0.2‐second period affects primarily one‐ and two‐story buildings while 1.0‐ second period of spectral acceleration affects buildings approximately 10 stories in height.

Robert T. Stafford Disaster Relief and emergency Assistance Act, PL 100‐707, signed into law November 23 1988: amended the Disaster Relief Act of 1974, PL 93‐288.

Where the unstable snow or ice breaks loose and starts to slide.

A settling or sinking of the earth’s crust.

The failure of a dam with the water level at the normal pool elevation and no rainfall.

Propagation of an earthquake‐generated fault rupture to the ground surface, displacing the surface and forming a scarp.

Subsidence (down dropping) and tilting of a basin on the down dropped side of a fault during an earthquake.

The margin of disturbed material most distant from the main scarp.

The slope or channel down which a snow avalanche moves at a fairly uniform speed.

Un‐cemented and non‐indurated sediment, chiefly clay, silt, sand, and gravel, deposited in basins.

A geographical area, usually of incorporated land, covered predominately by engineered structures including homes, schools, commercial buildings, service facilities, and recreational facilities.

The rate of displacement of an earth particle caused by passage of a seismic wave.

A normal fault that extends over 200 miles from Malad City, Idaho to Fayette, Utah, and trends along the western front of the Wasatch Range.

The area of land above a reference point on a stream or river, which contributes runoff to that stream.

A group of processes (such as the chemical action of air, rain water, plants, and bacteria and the mechanical action of temperature changes) whereby rocks on exposure to the weather change in character, decay, and finally crumble into soil.

Uncontrolled fire burning in vegetation.

A geographical area of unincorporated land covered predominately by natural vegetation.

Wildland vegetation and forested areas adjacent to or intermingled with residential developments.

The width of the area of surface faulting over which earth materials have been disturbed by fault rupture, tilting, or subsidence.