Glossary

FEMA has established certain requirements for the development and implementation of pre-disaster mitigation plans.  One of the elements of a quality plan is for emergency services experts to be able to easily update the data that drives the findings and strategies. 

Stakeholders in this plan are encouraged to submit documentation (maps, datasets, reports) that supports the information provided in the plan.  Users of the plan will be able to search these reference materials from this page.

Glossary of Terms

Seismicity

Seismic or earthquake activity.

Sensitive Clay

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

Shear Strength

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.

Shear Stress

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

Slope Failure

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

Slump

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

Snow Avalanche

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

Spectral Acceleration

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.

Stafford Act

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.

Starting Zone (avalanche)

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

Subsidence

A settling or sinking of the earth’s crust.

Sunny‐Day Failure

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

Surface fault rupture (surface faulting)

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

Tectonic Subsidence

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

Toe (landslide)

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

Track (avalanche)

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

Unconsolidated Basin Fill

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

Urban Area

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

Velocity (ground motion)

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

Wasatch Fault

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.

Watershed

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

Weathering

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.

Wildfire

Uncontrolled fire burning in vegetation.

Wildland Area

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

Wildland Urban Interface (WUI)

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

Zone of Deformation (earthquake)

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