Geology 1403 Exam 3

What is an earthquake

seismic waves or vibrations caused by the sudden release of energy, usually as a result of the displacement of rocks along faults

What causes earthquakes

energy released at plate boundary interactions

What are the locations of earthquakes

primarily along plate boundaries

-80% Circum-Pacific or Ring of Fire

-15% Mediterranean-Asiatic belt

examples: Japan, Chili & Haiti

-5% within plate interiors

examples: Missouri & small quakes in U.S., Australia

Examples of plate margin interactions

Africa, New Zealand, San Andres Mountain Ranges, CA

What is elastic rebound

the mechanism by which energy is released during earthquakes.

ex. 1906 San Francisco earthquake displaced a fence 15'

What is the Focus

hypocenter or the point within the Earth where fracturing or rupturing begins is first released at this point

seismic waves move from the focus

What is the Epicenter

the point on Earth's surface directly above the focus

What are the categories and focal depths of earthquakes

-Shallow focus is less than 70km at the crust and upper mantle

-intermediate-focus-is 70-300km at the astenosphere

-deep-focus is greater than 300km at the asthenosphere and possible lower mantle (only felt by seismic recordings)

What is a seismic wave

energy released at the focus of an earthquake radiates outward in all direction from the focus. This energy travels in the form of seismic or vibrating waves

What are the types of seismic waves

-Body waves travel through the solid body of the earth

Primary or P and Secondary or S Waves

-Surface waves travel along the ground surface and are slower

Rayleigh or R and Love or L Waves

What are P Primary Waves

-Fast

-Compressional or push-pull (slinky)

-move material back and forth in the direction of the wave

-travel through solid, liquid, gas or all mediums

What are S Secondary Waves

-slower than P-waves

-shear

-move material perpendicular to the direction of the wave producing shear stress

-travel through solids only

S's--slow, shear and solids

What are the Surface Waves

-R waves and L waves

What do surface waves do

generally produce a rolling or swaying motion, similar to standing on a boat

What type of wave is used to locate an earthquake

Body waves

What is intensity

a subjective measure of the kind of damage done and people's reactions to the quake. This is used by insurance companies

What is magnitude

the total amount of energy released by an earthquake at its source. This is measureable and might change with more information. ex. Richter magnitude scale measures

What does the Mercalli Intensity Scale do

provides a visual inspection of the damage and is qualitative

What are the destructive effects of earthquakes

-ground shaking or rupturing

-fire

-Tsunami

-Ground failure or landslides

-Liquifaction

What is ground shaking

ground moves or opens as a result of an earthquake. example Turkey earthquake 1999

What causes fire

results from earthquakes when gas and electrical lines break, more buildings in CA destroyed by fire

What is a Tsunami

Seismic sea wave caused by the disruption of the sea floor. Its energy is concentrated on shorelines and barely noticed in open seas. It travels great distances and causes damage far from its source

What is ground failure

land or mudslides caused by earthquakes, often in mountainous regions. Responsible for large numbers of deaths and destruction

ex. Madison River or Earthquake Lake

What is liquifaction

dependent on different types of geology where ground is liquified and can't support structures

ex. sand volcanoes, Niigata, Japan and Nuclear reactors in Japan 2011

What do successful earthquake predictions include

-timeframe for the occurrence

-location

-strength of the earthquake

results are mixed because of humannature

What is refraction

wave's direction and velocity change as it passes from one material to another of different density and elasticity. ex. light wave passing from air to water--straw in a glass of water

What is reflection

a wave is reflected back to the surface when encountering a boundary separating materials of different density or elasticity

ex. shiny surface-light bounces off and comes back

What is discontinuity

a boundary which occurs where there is a significant change in earth's material or properties

-basis for subdividing earth's interior into concentric layers

What is moho

boundary between earth's crust and mantle

What is seismic tomography

technique for mapping seismic wave paths so that slow and fast areas of earth's travel can be detected

What are faster seismic waves

-cold rocks

-beneath the older and interior parts of the continent

-no tectonic activity

What are slower seismic waves

-hot rocks

-beneath volcanic areas and mid-ocean spreading ridges-Hawaii

What do seismic tomography results tell us

a better picture of the earth's interior or a way to look at convection and how it relates to plate tectonics

What are the temperature estimates of the earth

-Base is hot

-Core to Mantle is hotter

-Center of core is hottest and closest to the temperature of the surface of the sun

What is the structure and composition of continental crust

-higher elevation

-thick

-less dense

-cannot be subducted

-felsic

-silica rich

-old

What is the structure and composition of oceanic crust

-below sea level

-thin

-more dense

-may be subducted

-mafic

-silica poor

-young

What is an ophiolite

slivers of oceanic crust and underlying mantle material preserved on the continents

-they don't match anything around them

What are the parts of continental margins

-continental shelf is the shallow area or

gentle sloping area between shore and slope

-shelf slope break is point of angle change or

where the angle of dip of the seafloor increases abruptly

-continetal slope is the relatively steep area between the shelf slope and and continental rise

-continental rise is gently sloping area from the base of the seafloor upwards towards the continental slope

What are the parts of deep ocean basins

-oceanic trenches are the site of subduction zones near convergent plate boundaries

-abyssal plains are flat, featureless surfaces of the seafloor

-oceanic ridges are mountainous at divergent margins and may develop a rift

-fractures are major offsets of the crust at transform margins

-submarine hydrothermal vents are at spreading ridges

-aseismic ridges are long, narrow ridges higher than the ocean floor without activity ex. Jan Mayen Ridge in N. America

-features of volcanic origin which differ in size ex. seamounts, guyots, abyssal hills

What are seamounts, guyots and abyssal hills

all of volcanic origin and differ in size

-seamounts Hawaii and volcanic island

-guyots are flat topped like the Hawaii Emperor's sea mount chain

-abyssal hills are hilly and smaller

What are turbidity currents

underwater flows of dense sediment-water mixtures

What are turbidity currents responsible for

the majority of sediment transport and deposition on the seafloor beyond the shelf-slope break

-gravity pulls sediment down and drops at abyssal plain with velocity, so it is formed by deposition of sediment based on gravity

Characteristics of turbidity currents

-gravity driven

-flow down submarine canyons

-base of the slope

-graded bedding

Describe Active Continental margins

-has tectonic boundary

-at convergent margins with subduction zones

-narrow continental shelf

-no continental rise

-slope descends into trench

-seismically and volcanically active

-young mountain range

ex. W coast of S. America, N. America and Andes Mountains

Describe Passive Continental margins

-no tectonic boundary

-develops within a plate, not at a boundary

-broad continental shelf

-slope & rise present

-abyssal plains are next to the rise

-lacks seismic and volcanic activity

-old mountain range, if present

ex. E coast of N. American, S. America and Appalachians

What are the conditions of the sea floor

dark, cold, pressure

What is pelagic

a term indicating the sediment settled from suspension far from land

-pelagic clay is red or brown

-pelagic ooze is mostly shells of marine organisms

What are reefs

mound-like, wave resistant structure composed of the skeletons of marine organisms close to continents in shallow water

ex. coral reefs or coral sponge, Cayman Islands, Key West, FL

What are the shapes of reefs

-fringing

-barrier

-atolls

What is deformation

a general term referring to any changes in the shape, volume or both of rocks

What is stress

the force applied to the rock to deform it

What is strain

deformation that results from stress

-strain and deformation can be the same

What are the 3 types of stress

-compression

-tension

-shear

What is compression

forces directed toward one another --><--, results in shortening of the rock layer by folding or faulting

What is tension

forces directed away from each other <-- -->

along the same line, resulting in lengthening or pulling apart of rock layers

What is shear

forces parallel but in opposite directions

-- >

<--

results in displacement of adjacent layers along closely spaced planes

What are the 3 types of strain

-elastic

-plastic

-fracture

What is elastic strain

deformed rocks return to their original shape when the stress is released

What is plastic strain

deformed rocks are folded and do not return to their original shape at great depths

What is fracture strain

deformed rocks are brittle and break and do not return to original shape at shallower depths

What determines elastic, plastic or fracture

rocks at depths are always more ductile than the same rocks at the surface

-stress applied

-pressure

-temperature

-time

-rock type

How do geologists describe the orientation or attitude of rock layers

-strike

-dip

What is strike

the compass direction of a line formed by the intersection of the horizontal and the rock unit/surface

What is dip

the measure of the angle between the horizontal plane and the rock unit

What are geologic structures

features resulting from deformation or strain to the shape or volume of rock units

What are the 2 types of geologic structures

-folds

-fractures

What are the 3 types of basic folds

-monocline

-anticline

-syncline

What is a monocline

a simple bend in horizontal or uniformly dipping layers, 1 bend

ex. Negev Desert, Israel

What is an anticline

an up arch

-convex

-rock layers dip away

-oldest rocks at the core

ex. Sheep mountain, WY

What is a syncline

a down arch

-concave

-rock layers dip toward

-youngest rocks exposed at the core

What are the parts of a fold

-axis or center of the fold

-axial plane or divides the fold into halves

-limb or half of a fold

What type of folds are anticlines and synclines

elongate folds where their length greatly exceeds their width

What types of folds are circular or oval

-dome or layers dip outward

-basin or layers dip inward

What are the 2 types of fractures

-joints

-faults

What are joints

fractures with no movement along the fracture surface, break apart

ex. Arches National Park, UT

What are faults

fractures with movement along the fracture surface, break and move

What are the parts of a fault

-fault plane or surface where movement takes place

-hanging wall or rock overlying or hanging over the plane

-foot wall or rock beneath the plane

What are the types of faults

-normal

-reverse

-thrust

-strike slip

-oblique slip

What is a normal fault

-hanging wall down

-lengthens

-tension pull apart

ex. Sierra Nevada range

What is a reverse fault

-hanging wall up

-shortens

-compression

ex. convergent plate margins

What is thrust fault

-reverse fault with a very low dip angle

-compression and plate margin interactions

ex. Lewis Overthrust, MT

What is strike-slip fault

exhibit horizontal movement

-common at transform plate margins

ex. San Andreas fault

What is oblique-slip faults

least common

-combination of strike-slip and dip-slip movements

What causes mountain building

all large mountain ranges on continents result from compression at convergent plate margins, plate tectonics

What are the examples of active convergent margin mountain ranges

-Andes

-Rocky mountains

-Japan

-Phillipines

-New Zealand

-Meditteranean Belt

What is a mountain

an area of land which is significantly higher than the surrounding land

ex. Grand Teton

What is a mountain range

a linear association of peaks and ridges which are related in age and origin

ex. Teton range

What is a mountain system

a complex, linear zone of deformation and crustal thickening that may contain several or many mountain ranges

ex. Rocky mountains or Himalayas

What is orogeny

an episode of mountain building with

-intense deformation

-regional metamorphism

-igneous activity

-thickening of the earth's crust

What are the 3 types of convergent plate margin interactions

-oceanic to oceanic

-oceanic to continental plate boundaries

-continental to continental plate boundaries

What is oceanic to oceanic plate interaction

forms an island arc

ex. Japan

What is oceanic to continental plate interaction

active volcanism and a submarine trench offshore

ex. Andes Mountains

What is continental to continental plate interaction

no subduction zone and extreme crustal thickening

ex. Himalayas

What is continental accretion

a process which adds material to the continent during an orogeny

-sediments added

-terranes

-ophiolites

What is a terrane

blocks of continental crust which do not match the surrounding crust

What is ophiolites

slivers of oceanic crust which are scraped off the subducting plate and preserved on another continent

What is the principle of isostasy

idea that the earth's crust floats in the mantle, floating equilibrium like wood in water

What is isostatic rebound

response of the earth's crust to change in the weight of the crust either from erosion of sediments or melting of continental glacial ice