Natural Hazards & Disasters exam 1

natural hazard

a natural process and event that is a potential threat to human life and property.

natural disaster

hazardous event that occurs over a limited time s[an within a defined area.

catastrophe

massive disaster that requires significant expediture of money and a long time (often years) for recovery to take place.

risk

the product of the probability of an event occuring multiplied by the consequences should it occur.

as a concept, rick is the product of hazard, exposure, and vulnerability.

magnitude-frequency concept

that the frequency of an event is inversely related to the magnitude. ie, high magnitude events are rare while low magnitude events are common.

mitigation

the avoiding of, lessening, or compensation for anticipated harmful effects of an action, especially with respect to the natural environment.

geology

interdiscipllinary science that studies the history, composition, internal structures, surface features, and natural processes of the earth.

catastrophism

geologic view that the earth is shaped by catastrophic events.

gradualism

geologic view that the earth is shaped by gradual changes over long periods of time.

principle of uniformitarianism

Principle that the same natural processes that we observe now are the same ones that have always occured. Suggests that “the present is the key to the past” and implies that “the present is the key to the future”

natural service functions

benefits that arise from a natural events; ex: nutrients in a floodplain, flushing pollutants, damn formations.

lithosphere

The outer layer of earth, approximately 100km (~60mi) think, which comprises the tectonic plates that contain the ocean basins and continents; includes both Earth’s crust and the solid, upper part of the mantle.

(lithos = “rock”)

asthenosphere

Upper zone of Earth’s mantle, located directly below the lithosphere; a hot, slowly flowing layer of relatively weak rock upon which tectonic plates move.

(asthenos = “without strength”)

Mohorovičić discontinuity

(aka the “Moho”)

The compositional boundary that separates the less dense crust from the higher-density rocks of the mantle below.

mantle convection

The driving mechanism of plate tectonics. The verticle transfer of heat and material within the Earth’s mantle, where how, less dense fluid rises and cooler, denser fluid sinks.

continental drift

Hypothesis proposed by Alfred Wegender, in 1915, that states the continental landmasses of the world “drift” about the surface of the globe and were once united to form a single super-continent, Pangaea. Wegener’s primary evidence for it was based on the congruity of the continents’ shapes and the similarities of fossils on different continents.

seafloor spreading

The plate tectonic concept that new crust is continuously added to the edges of lithospheric plates at divergent plate boundaries as a result of upwelling of magma along mid-ocean ridges (Earth’s interior center rises to fill the void space and then cools, adding to new oceanic lithosphere to the plate edge.)

hotspot

A hypothesized, nearly stationary heat source located below the lithosphere that feeds overlying volcanic processes near Earth’s surface.

earthquake cycle

Proposes that there is a drop in elastic strain after an earthquake and an accumulation of strain before the next strain. Would explain the periodic nature of earthquakes on a given fault.

normal fault

Identified by downward movement of the hanging wall relative to the footwall. Caused by tensional stress, results in extension & thinning of Earth’s crust typical of divergent plate boundary.

reverse fault

Identified by an upward relative movement of the hanging wall due to compression which results in shortening * thickening of Earth’s crust typical of convergent plate boundaries. A low-angle reverse faul is called a thrust fault.

strike-slip fault

A fracture or fracture system along which a block of Earth’s crust moves horizontally relative to the block on the opposite side of the fracture.

focus

In an earthquake, the point or location in Earth of the initial break of rupture, and from which energy is first released; during an earthquake, seismic energy radiates out from this point or location. aka, hypocenter

epicenter

The point on Earth’s surface directly above the focus of an earthquake; the focus is the area that first ruptures on a geologic fault in an earthquake.

seismic waves

Released stored elastic strain from when a fault ruptures and rock breaks apart suddenly and violently. They radiate outward from the focus. Seismic waves are what are perceived as the earthquake.

seismograph

Instrument that records earthquakes through the movement of the earth at a specific location, aka seismometer.

seismogram

A written or digital graphic record made by a seismograph.

moment magnitude

A numerical assessment from the 1970s that is used to determine the absolute size of an earthquake by measuring the actual energy released during the earthquake. Can take days to months to calculate properly.

Mercalli intensity scale

A scale with 12 divisions, expressed in Roman Numerals, on which the amount and severity of shaking and damage from an earthquake can be ranked.

material amplification

Increase in the amplitude of seismic shaking caused by some earth materials. Such increase is generally associated with soft sediments, such as silk and clay deposits. Strongly influences the amount of ground motion felt.

liquefaction

transformation of water-saturated granular material from the solid state to a liquid state.