geology exam 2 study guide 2

ch 13, 9, 8 and interlude D

fault

fracture which one body of rock slides past another

seismicity

earthquake activity

seismic waves

waves of energy emitted at the focus of an earthquake

displacement

amount of movement or slip across a fault plane

fault scarp

a small step on the ground surface where one side of a fault has moved vertically in respect to another

stress

push, pull or shear that a material feels when subjected to a force

elastic rebound theory

earth quakes happen because of stress built up causing rock adjacent to a fault to bend elastically until breaking

stick-slip behavior

stop-start movement along a falut plane caused by friction, prevents movement til stress builds up

mainshock

largest earthquake during a succession of earthquakes

foreshock

smaller earthquakes that precede major earthquake

focus (hypocenter)

location where a fault slips during earthquake

epicenter

point on the surface of the earth directly above the focus of earthquake

body wave

siemsic wave that pass through interior of the earth

surface wave

seismic waves that travel on surface of the earth

compressional wave

waves where particles move back and forth parallel to the direction in which the wave itself moves

shear wave

seismic waves which particles move back and forth perpendicular to direction the wave moves

modified mercalli intensity (MMI) scale

earthquake characterization scale based on the amount of damage an earthquake causes

earthquake magnitude

representation of energy released by an earthquake, indicated by the amplitude of seimsic waves

richter scale

a scale that defines earthquakes on the basis of the amplitude of the largest ground motion recorded on a seimsogram

seismic belt

relatively narrow strips of crust on the earth under which most earthquakes occur

seismic zone

region in which earthquakes happen fairly frequently

megathrust earthquakes

largest type of earthquake, can trigger large tsunamis

wadati-benioff zone

slopping band of seismicity defined by intermediate and deep focus earthquakes that occur in the downgoing slab of a convergent boundary

intraplate earthquakes

occur away from plate boundaries

sediment liquefaction

pressure in the water in the pores push sediment grains apart, and sediment becomes able to flow like a liquid

earthquake early warning system

communications network that provides an alert within microseconds after the first waves arrive but before damaging vibrations reach population centers

seismic ray

changing position of an imaginary point on a wave front as the front moves through a rock

reflection

when energy bounces off a boundary, the incoming angle and outgoing angle are equal

refraction

bending of a ray as it passes through a boundary btwn two different materials

low velocity zone

asthenosphere underlying oceanic lithosphere where seismic waves travel slowly

seismic tomography

computers create a three dimensional image of variations in seismic wave velocities within the earth

viscosity

resistance of a material to flow

the more silica in the magma the

higher its viscosity

felsic magma

has the most silica, high viscosity, lower temp and explosive eruptions

mafic magma

higher temp, low silica, low viscosity and effusive eruptions

orogen

a linear range of mountains

orogeny

a mountain building event

stress

push, pull or shear that a material feels when subjected to a force

joints

naturally formed cracks in rocks

vein

a seam of minerals that forms when dissolved ions carried by water solutions precipitate in cracks

strike

the compass of a horizontal line on a plane

fault

a fracture on which one body of rock slides past another

displacement

amount of movement or slip across a fault plane

dip-slip fault

a fault in which sliding occurs up or down the slope of the fault

reverse fault

a steeply dipping fault on which the hanging wall block slides up

thrust fault

a gently dipping reverse fault, hanging wall moves up

normal fault

fault in which the hanging wall block moves down the slope of the fault

strike slip fault

a fault in which one block slides horizontally past another

oblique slip fault

fault where sliding occurs diagonally along the fault plane

fault scarp

a small step on the ground surface

slickensides

polished surface of a fault caused by slip on the fault; groves indicate the direction of the fault movement

axial surface

the imaginary surface that encompasses the hinges of successive layers of a fold

anticline

a fold with an arch like shape in which the limbs dip away from the hinge

syncline

a trough shaped fold whose limbs dip toward the hinge

monocline

a fold in the land surface whose shape resembles that of a carpet draped over a stair step

foliation

layering formed as a consequence of the alignment of mineral grains, or compositional banding in a metamorphic rock

suture

contact defining the boundary of what were two separate crustal blocks, prior to collision

accretion

the addition of new crust to a continent by collision of island arcs and oceanic plateaus

isostasy

the condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling the lithosphere down

orogenic collapse

the process in which mountains begin to collapse under their own weight and spread out

shield

older, interior region of a continent

regolith

any kind of unconsolidated debris that covers bedrock

mass wasting

the gravitationally caused downslope transport of rock, regolith, snow or ice

landslide

sudden movement of rock and debris down a non-vertical slope

creep

gradual downslope movement of regolith

soliflucation

type of creep characteristic of tundra regions; permafrost melts and then the soggy weak layer of ground flows slowly downslope

slump

semi-coherent volume of regolith that slipped down a slope above a spoon shaped failure surface at slow to moderate speed

failure surface

a weak surface that forms the base of a landslide

debris slide

sudden downslope of movement of material consisting only of regolith

debris flow

downslope of movement of mud mixed with larger rock fragments

talus

sloping apron of fallen rock along the base of a cliff

turbidity current

a submarine avalanche of sediment and water that speeds down a submarine slope

angle of repose

angle of the steepest slope that a pile of uncemented material can attain without collapsing from the pull of gravity

riprap

loose boulders or concrete piled together along a beach to abosrb wave energy before it strikes a cliff face