Geology Final Exam

earthquake intensity

-a representation of the strength of an earthquake
-based on the amount of damage due to the event and on people's perception of ground shaking during the event
-intensity is measured with the Mercalli scale; intensity decreases with increasing distance from the epicenter

Modified Mercalli Intensity (MMI) Scale

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

earthquake magnitude

-a representation of the energy released by an earthquake
-as indicated by the amplitude of specific seismic waves as they would be recorded by a seismometer at a set distance from the epicenter

earthquake amplitude

the amount of up-and-down or back-and-forth motion of the ground—the larger the amplitude
-the greater the deflection of a seismometer pen or needle as it traces out a seismogram

richter scale

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

seismogram

The record of an earthquake produced by a seismometer

travel-time curve

a graph that plots the time since an earthquake began on the vertical axis and the distance to the epicenter on the horizontal axis

Seismologists find that earthquakes take place on

most seismic belts or seismic zones

The majority of earthquakes happen on faults along plate boundaries because

the relative motion between plates causes slip on faults

damaging effects of earthquakes

-building collapse
-buried pipes break
-fires
-liquifaction
-tsunami
-sanitation

fire during earthquakes occurs when

leaked fuel and electrical transmission lines mix

liquifaction

occurs when an earthquake's violent shaking suddenly turns loose, soft soil into liquid mud

tsunami

a giant wave usually caused by an earthquake beneath the ocean floor

S-wave shadow zone

A band between 103° and 180° from the epicenter of an earthquake inside of which S-waves do not arrive at seismograph stations

seismic topography

analysis by sophisticated computers of global seismic data in order to create a three-dimensional image of variations in seismic-wave velocities within the Earth

seismic velocity

velocity

the speed of an object in a particular direction

depth

downward measurement from a surface

crust

The thin and solid outermost layer of the Earth above the mantle

mantle

The layer of hot, solid material between Earth's crust and core

lithosphere

the solid, outer layer of the earth that consists of the crust and the rigid upper part of the mantle
-100- 150 km

asthenosphere

upper mantle and below the lithosphere (200- 500 km); "weak" (soft) sphere

lithostatic pressure

-pressure exerted on rocks by the weight of overlying rocks
-uniform pressure that "feels" the same from all directions

differential stress

stress applied unequally in different directions

force

A push or pull exerted on an object

surface area

the sum of all the areas of all surfaces of a solid

stress

-the push, pull, or shear that a material feels when subjected to a force
-formally, the force applied per unit area over which the force acts

types of stress

compressive, tensile, shear

compressive stress

A stress due to a force pushing together on a rock

tensional stress

occurs when a rock is pulled apart

shear stress

develops when one part of a rock body moves sideways past another
-in general, the stress acting in one direction is not the same magnitude as the stress acting in another direction

deformation

the bending, tilting, and breaking of Earth's crust
-the change in the shape of rock in response to stress

types of deformation

displacement, rotation, change of shape (strain)

displacement

the amount of movement or slip across a fault plane
-a change in location

rotation

change in orientation or position

change of shape (strain) (distortion)

change in shape of a rock

strain

the change in shape of an object in response to deformation
-response to stress

type of strain

elastic, brittle, ductile

elastic strain

change in rock that is not permanent
-when stress is removed rock goes back to original shape
-does not break
-spontaneous recovery
-w/o loss of cohesion
-delta shape

plastic (ductile) strain

the deformational process in which mineral grains behave like plastic
-when compressed or sheared, become flattened or elongated without cracking or breaking
-permanent form after strain
-w/o loss of cohesion
-delta shape

brittle strain

the cracking and fracturing of a material subjected to stress
-loss of cohesion
-permanent

factors that effect type of strain

-heat (temp)
-pressure
-rate (time)
-water

heat

hot - plastic (ductile)
cold - elastic and brittle

pressure

high pressure - plastic (ductile)
low pressure - elastic and brittle

rate (time)

slow - plastic (ductile)
rapid - elastic and brittle

water

weakens rock

vein

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

strike

The compass orientation of a horizontal line on a plane
-an imaginary horizontal line on the plane and the direction to true north

dip

The angle of a plane's slope as measured in a vertical plane perpendicular to the strike

dip direction

the compass direction of the dip measured at right angles to the strike
-always perpendicular to the line of strike

types of faults

normal, reverse, strike-slip, dip-slip

strike-slip fault

a fault in which one block slides horizontally past another (and therefore parallel to the strike line), so there is no relative vertical motion

left-lateral (sinistral)

left-lateral (sinistral)
used in describing strike-slip faults if the rock of the other side of the fault moves to the left
-If the block on the far side slipped to your left

right-lateral (dextral)

used in describing strike-slip faults if the rock on the other side of the fault moves to the right
-If the block on the far side slipped to your right

dip-slip fault

movement parallels the dip line, a line going down the slope of the fault surface
-normal and reverse fault

normal fault

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

reverse fault

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

oblique-slip fault

a fault with both strike-slip and dip-slip components

A horizontal plane has a dip of 0 degrees and

a vertical plane has a dip of 90 degree

fold types

anticline and syncline

thrust fault

a gently dipping reverse fault

anticline

Folds that have an archlike shape in which the limbs dip away from the hinge
-represents an arch-like shape
-compression causes anticlines

syncline

A trough-shaped fold whose limbs dip toward the hinge
-represents a trough
-compression causes synclines

relative age (time)

a sequence of events

numerical (absolute) age (time)

The age of a feature given in years
-carbon dating (radiometric dating)
-tree rings
-lichenometry

radiometric dating

method used to determine the age of rocks using the rate of decay of radioactive isotopes

geologic time scale

represents the duration of this history
-scale used by paleontologists to represent evolutionary time

geologic principles for determining relative age

-created by Charles Lyell
uniformitarianism, cross-cutting relations, superposition

uniformitarianism

-created by James Hutton; Lyell made it popular
-means that physical processes we observe operating today also operated in the past, at roughly comparable rates

cross-cutting relations

If one geologic feature cuts across another, the feature that has been cut is older
-if a layer of sediment buries a fault, the layer must be younger than the fault

The principle of superposition:

the principle that in a series of stratified sedimentary rocks the lowest stratum is the oldest
-the layer at the bottom of a sequence is the oldest, and the layer at the top is the youngest

fossil succession

states that the assemblage of fossils in strata changes from base to top of a sequence
-created by William Smith

geologic time scale diagram

era

An interval of geologic time representing the largest subdivision of the Phanerozoic Eon
-paleozoic, mesozoic, cenozoic

period

An interval of geologic time representing a subdivision of a geologic era
-ex: triassic

epoch

An interval of geologic time representing the largest subdivision of a period
ex: holocene of the quaternary period

K-T boundary

the Cretaceous period and rocks of the Paleogene period that provides evidence of a meteorite impact
T= also equals tertiary

Phanerozoic Eon

most recent eon, include the past 542 million years, divided into 3 eras
-paleozoic, mesozoic, cenozoic

Paleozoic Era

the part of geologic time 570-245 million years ago ; invertebrates, fishes, amphibians, reptiles, ferns, and cone-bearing trees were dominant

Cambrian explosion (part of paleozoic era)

A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geologic history; recorded in the fossil record about 545 to 525 million years ago
-big animals evolved

Devonian Period

The Paleozoic age of fishes

silurian period (part of paleozoic era)

The period with the first plants
-rapid evolution of plants

unconformity

a boundary between two different rock sequences representing an interval of time during which new strata were not deposited and/or were eroded

types of unconformities

angular, disconformity, nonconformity

Strata

layers of sedimentary rock

angular unconformity

the strata below were tilted or folded before the unconformity developed

disconformity

an unconformity parallel to the two sedimentary sequences it separates

nonconformity

sedimentary rocks overlie generally much older intrusive igneous rocks or metamorphic rocks

the grand staircase

grand canyon, zion canyon, and bryce canyon

radioactive decay

The process by which a radioactive isotope undergoes fission or releases particles, thereby being transformed into a new element

radioactive parent

an atom of a radioactive isotope that has not yet decayed

radiogenic daughter

the product of a radioactive decay

half life

the time it takes for half of a group of a radioactive element's isotopes to decay

Graphic representation of parent and daughter atoms vs. half life

half life equation

t1/2 = 0.693/k
k= number of atoms/number of decays

2,500 parent atoms and 17,500 daughter atoms requires

3 half lives
t1/2= 20 MY
age= 60 MY

isotope systems

Carbon-14, C^14 Nitrogen-14, N^14
Potassium-40, K^40 Argon-40, Ar^40
Uranium-238, U^238 Lead-206, Pb^206
Rubidium-87, Rb^87 Strontium-87, Sr^87

Determining numerical (absolute) age of sedimentary rocks

-Studying cross cutting relationships between sedimentary rocks and datable igneous or metamorphic rocks.
-The Geologic Time Scale: A scale that describes the intervals of geologic time

age of earth

4.56 Ga

Lord Kelvin (William Thomson)

-1862- 1897
calculated earth was 20 MY old