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

Abutment (dam)

The valley-side against which a dam is constructed.

Acre‐foot of Water

Approximately 326,000 gallons of water, or approximately a football field covered by one foot of water.

Active Faults

An active fault is defined as a fault displaying evidence of displacement along one or more of its traces during Holocene time (about the last 11,000 years).

Aftershocks

Earthquakes during the seconds, hours, days to months following a larger earthquake (main shock) in the same general region.

Alluvial Fan

A cone‐shaped deposit of stream sediments, generally deposited at the base of a mountain where a stream encounters flatter terrain.

Amplitude (seismic waves)

The maximum height of a wave crest or depth of a trough. Amount the ground moves as a seismic wave passes, as measured from a seismogram.

Avalanche Path

The area in which a snow avalanche runs; generally divided into starting zone, track, and runout zone.

Basin and Range Physiographic Province

Consists of north‐south‐trending mountain ranges separated by valleys, bounded by the Rocky Mountains and the Colorado Plateau to the east and the Sierra‐ Cascade Mountains to the west (includes western Utah).

Bearing Capacity

The load per unit area, which the ground can safely support without excessive yield.

Bedrock

Solid in‐place rock, sometimes exposed and sometimes concealed beneath the soil.

Block Faulting

see normal fault

Collapsible Soil (hydrocompaction)

Loose, dry, low‐density soil that decreases in volume or collapses when saturated for the first time following deposition.

Critical Areas

Environmentally sensitive areas which include wetlands fish and wildlife habitat conservation areas; geologically hazardous areas; areas with a critical recharging effect on aquifers used for potable water; and frequently flooded areas. Critical areas have measurable characteristics which, when combined, create a value for or potential risk to public health, safety and welfare.

Critical/Essential Facilities

Structures meeting one or more of the following criteria: 

  • Fire stations, police stations, storage facilities for vehicles/equipment needed after a hazard event, and emergency operation centers.
  • Hospitals, nursing homes, and housing which is likely to contain occupants who may not be sufficiently mobile to avoid injury or death as a result of a hazardous event.
  • Public and private utility facilities, which are vital to maintaining or restoring normal services to, damaged areas after a hazardous event. 
  • Structures or facilities that produce, store, or use highly flammable, explosive, volatile, toxic and/or water-reactive materials.

Debris Flow

Involves the relatively rapid, viscous flow of surficial material that is predominantly coarse grained.

Debris Slide

Involves predominantly coarse‐grained material moving mainly along a planar surface.

Drought (Agricultural)

Lack of water for crop production in a given area.

Drought (Hydrologic)

Lack of water in the entire water supply for a given area.

Drought (Meteorological)

Lack of precipitation compared to an area’s normal.

Drought (Socioeconomic)

Lack of water sufficient to support an area’s population.

Earth Flow

Involves fine‐grained material that slumps away from the top or upper part of a slope, leaving a scarp, and flows down to form a bulging toe.

Earthquake

A sudden motion or trembling in the earth as fracture and movement of rocks along a fault release stored elastic energy.

Earthquake Fault Zone

Earthquake fault zones are regulatory zones around active faults. The zones are used to prohibit the location of critical facilities and structures designed for human occupancy from being built astride an active fault. Earthquake Fault Zones are plotted on topographic maps at a scale of 1‐inch equals 2,000 feet. The zones vary in width, but average about one‐quarter mile wide.

Earthquake‐induced Seiche

 Earthquake generated water waves causing inundation around shores or lakes and reservoirs.

Epicenter

The point on the earth’s surface directly above the focus of an earthquake.

Epoch

Geologic time unit lasting more than an age but shorter than a period (Epoch 2008).

Erosion

The removal of earth or rock material by many types of processes, for example, water, wind, or ice action.

Expansive Soil and Rock

Soil and rock which contain clay minerals that expand and contract with changes in moisture content.

Fault

A break in the earth along which movement occurs.

Fault Segment

Section of a fault that behaves independently from adjacent sections.

Fault Zone

An area containing numerous faults.

Federal Emergency Management Agency (FEMA)

Authorized under Section 404 of the Stanford Act. Provides funding for hazard mitigation projects that are cost‐effective and comply with existing post-disaster mitigation programs and activities. These projects cannot be funded through other programs to be eligible.

Fill

Material used to raise the surface of the land generally in a low area.

Fire‐resistant Vegetation

Plants that do not readily ignite and burn when subjected to fire because of inherent physiological characteristics of the species such as moisture content, fuel loading, and fuel arrangement.

Floodplain

An area adjoining a body of water or natural stream that has been or may be covered by floodwater.

Floodplain (100‐year/500‐year)

Floodplains that have the potential to flood once every 100 or 500 years or that has a 1% (100‐year) or 0.2% (500‐year) chance of flooding equal to or in excess of that in any given year.

Floodway

An area of land immediately adjacent to a stream or river channel that, in times of flooding, becomes an enlarged stream or river channel and carries the floodwater with the highest velocity.

Fluvial

Concerning or pertaining to rivers or streams.

Focus

The point of origin of an earthquake within the earth, and the origin of the earthquake’s seismic waves.

Formation (geologic)

A mappable rock unit consisting of distinctive features/rock types separate from units above and below.

Frequency (seismic waves)

The number of complete cycles of a seismic wave passing a point during one second.

Fuel (fire)

Vegetation, building material, debris, and other substances that will support combustion.

Fuel Break

A change in fuel continuity, type of fuel, or degree of flammability of fuel in a strategically-located strip of land to reduce or hinder the rate of fire spread.

Fuel Type

A category of vegetation used to indicate the predominate cover of an area.

Glacial Moraine

Debris (sand to boulders) transported and deposited by glacial ice along a glacier’s sides or terminus.

Graben

A block of earth dropped between two faults.

Gradient (slope)

A measure of the slope of the land surface.

Ground Failure

A general term referring to any type of ground cracking or subsidence, including landslides and liquefaction‐induced cracks.

Ground Shaking

The shaking or vibration of the ground during an earthquake.

Ground Water

That portion of subsurface water which is in the zone of saturation.

Gypsiferous Deposits

Soil or rock containing gypsum, which can be subject to dissolution.

Gypsum

A mineral composed of hydrated calcium sulfate. A common mineral of evaporites.

Hazard Mitigation

Any action taken to reduce or permanently eliminate the long‐term risk to human life and property and the environment posed by a hazard.

Hazard Mitigation Plan

The Plan resulting from a systematic evaluation of the nature and extent of vulnerabilities posed by a hazard present in society that includes the strategies needed to minimize future vulnerability to hazards.

HAZUS‐MH – Hazards United States

Multihazards; Earthquake loss estimation software using GIS databases developed by FEMA.

Head (landslide)

The upper parts of the slide material along the contact between the disturbed material and the main scarp.

Holocene

Geologic epoch covering the last 10,000 years (after the last Ice Age).

Igneous Rocks

Rocks formed by cooling and hardening of hot liquid material (magma), including rocks cooled within the earth (for example, granite) and those that cooled at the ground surface as lavas (such as basalt).

Impermeable

Materials having a texture that does not permit water to move through.

Interfluve

Land between two streams in the same drainage basin (Interfluve 2004).

Intermountain Seismic Belt (ISB)

Zone of pronounced seismicity, up to 120 miles wide and 800 miles long, extending from Arizona through central Utah to northwestern Montana.

Lacustrine

Concerning or pertaining to lakes.

Lake Bonneville

A large, ancient lake that existed 30,000 to 12,000 years ago and covered nearly 20,000 square miles in Utah, Idaho, and Nevada. The lake covered many of Utah’s valleys, and was almost 1,000 feet deep in the area of the present Great Salt Lake.

Lake Bonneville Sediments

Sediments deposited by Lake Bonneville, found in the valleys, which range from gravels and sands to clays.

Landslide

A general term for a mass of earth or rock, which moves down slope by flowing, spreading, sliding, toppling, or falling (see slope failure).

Lateral Spread

Lateral down slope displacement of soil layers, generally several feet or more, above a liquefied layer.

Levee (flood)

A berm or dike used to contain or direct water, usually without an outlet or spillway.

Liquefaction

Sudden large decrease in shear strength of a cohesionless soil (generally sand or silt) caused by collapse of soil structure and temporary increase in pore‐water pressure during earthquake ground shaking.

Magnitude (earthquake)

A quantity characteristic of the amplitude of the ground motion of an earthquake. The most commonly used measurement is the Richter magnitude scale; a logarithmic scale based on the motion that would be measured by a standard type of seismograph 60 miles from the earthquake’s epicenter.

Metamorphic Rocks

Rocks formed by high temperatures and/or pressures (for example, quartzite formed from sandstone).

Mitigation

The act of reducing or preventing hazards which affect society or those things deemed important to society.

Modified Mercalli Intensity (MMI)

The most commonly used intensity scale in the U.S.; it is a measure of the severity of earthquake shaking at a particular site as determined from its effect on the earth’s surface, man, and man’s structures.

Montmorillonite

A clay mineral characterized by expansion upon wetting and shrinking upon drying.

Natural Vegetation

Native plant life existing on a piece of land before any form of development.

Normal Fault (block faulting)

Fault caused by crustal extension in which relative movement on opposite sides is primarily vertical; for example, the Wasatch Fault.

Oolite

Spherical grains of carbonate sand with a brine shrimp fecal pellet nucleus.

Outlet (dam)

A conduit through which controlled releases can be made from the reservoir.

Palmer Drought Severity Index (PDSI)

Developed by Wayne Palmer in 1965; measures drought severity using temperature, precipitation and soil moisture (Utah Division of Water Resources 2007).

Peat

Unconsolidated surficial deposit of partially decomposed plant remains.

Period (geologic)

A standard (world‐wide) geologic time unit.

Permeability

The capacity of a porous rock or soil for transmitting a fluid.

Physiographic Province

A region whose pattern of relief features or landforms differs significantly from that of adjacent regions.

Piping (problem soil and rock)

A weak incoherent layer in unconsolidated deposits that acts as a channel directing the movement of water. As the layer becomes saturated it conducts water to a free face (cliff or stream bank for example) that intersects the layer, and material exits out a “pipe” formed in the free face. Piping can occur in a dam as the result of progressive development of internal erosion by seepage.

Pore Space

The open spaces in a rock or soil between solid grains. The spaces may be filled with gas (usually air) or liquid (usually water).

Porosity

The ratio of the volume of pore space in rock or soil to the volume of its mass, expressed as percentage.

Probable Maximum Flood (PMF)

A flood that would result from the most severe combination of critical meteorological and hydrologic conditions possible in a region.

Probable Maximum Precipitation (PMP)

The maximum amount and duration of precipitation that can be expected to occur on a drainage basin.

Problem Soil and Rock

Geologic materials that are susceptible to volumetric changes, collapse, subsidence, or other engineering geologic problems.

Project Impact

An initiative of the Federal Emergency Management Agency intended to modify the way in which the United States handles natural disasters. The Goal of Project Impact from a Federal Government perspective is to reduce the personal and economic costs of hazard events by bringing together the private and public sector to better enable the citizens of a community to protect themselves from natural hazards.

Quaternary

A geologic time period covering the last 1.6 million years.

Recurrence Interval

The length of time between occurrences of a particular event (an earthquake, for example).

Rock Fall

Abrupt free fall or down slope movement, such as rolling or sliding, of loosened blocks or boulders from an area of bedrock. The rock‐fall runout zone is the area below a rock‐fall source which is at risk from falling rocks.

Rock Topple

Forward rotation movement of a rock unit(s) about some pivot point.

Runout Zone (avalanche)

Where a snow avalanche slows down and comes to rest (deposition zone). For large avalanches, the runout zone can include a powder‐ or wind‐blast zone that extends far beyond the area of snow deposition.

Sand Blow (earthquake)

Deposit of sandy sediment ejected as water and sand to the surface, formed when ground shaking has caused liquefaction at depth.

Scarp

A relatively steeper slope separating two more gentle slopes. Scarps can form as a result of earthquake faulting.

Sediment

Material that is in suspension, is being transported, or has been moved from its site of origin by water, ice, or wind, and has come to rest on the earth’s surface either above or below the sea level.

Sedimentary Rocks

Rocks formed from loose sediment such as sand, mud, or gravel deposited by water, ice, or wind, and then hardened into rock (for example, sandstone); or formed by dissolved minerals precipitating out of solution to form rock (for example, tufa).

Seiche

A standing wave generated in a closed body of water such as a lake or reservoir. Ground shaking, tectonic tilting, sub aqueous fault rupture, or landsliding into water can all generate a seiche.

Seismic Waves

Vibrations in the earth produced during earthquakes.