Geology Terms From Chapter 8 Of Essentials Of Geology

Front 1

Earthquakes:

Define the epicenter

Back 1

The point on the surface of the Earth that lies directly above the hypocenter.

Front 2

Earthquakes:

Define displacement

Back 2

The amount of slip on the fault.

Front 3

Earthquakes:

Define what a fault scarp is

Back 3

In places where an active normal or reverse fault intersects the ground, movement on the fault displaces the ground surface and generates a small step.

Front 4

Earthquakes:

Define the Elastic-Rebound Theory

Back 4

The concept that earthquakes happen in a region of lithosphere because stresses build up, causing rock to bend elastically until slip on a fault occurs, at which time elastic bending decreases.

Front 5

Earthquakes:

Define foreshocks

Back 5

Small earthquakes that occur before a major earthquake.

Front 6

Earthquakes:

Define aftershocks

Back 6

Smaller earthquakes that follow a major earthquake. May occur for days after or even weeks after.

Front 7

Earthquakes:

Define seismic waves

Back 7

Earthquake waves. You can feel an example of them if you touch one end of a brick and tap the other with a hammer.

Front 8

Earthquakes:

Define body waves

Back 8

Waves that pass through the interior of the Earth.

Front 9

Earthquakes:

Define surface waves

Back 9

Waves that pass along the surface of the Earth. These are the waves that cause the most damage.

Front 10

Earthquakes:

Define what a seismograph is

Back 10

Can systematically record the ground motion from an earthquake happening anywhere on Earth.

Front 11

Earthquakes:

Define a seismogram

Back 11

The waves traced by the pen on a seismograph provides a record the earthquake called a seismogram.

Front 12

Earthquakes:

Define magnitude

Back 12

A number that indicates its relative size as determined by measuring the maximum amplitude of ground motion recorded by a seismograph.

Front 13

Earthquakes:

What is the Richter Scale?

Back 13

A concept of defining and measuring earthquake magnitude. Developed by Charles Richter.

Front 14

Earthquakes:

What are seismic belts?

Back 14

They define plate boundaries. Earthquakes within these belts are plate-boundary earthquakes

Front 15

Earthquakes:

What is liquefaction?

Back 15

The abrupt loss of strength of a wet sediment (either sediment or clay) in response to ground shaking.

Front 16

Earthquakes:

What are seismic gaps?

Back 16

A locked fault segment that has not experienced seismic activity for a long time. Because stress tends to accumulate in seismic gaps, they often become the sites of major earthquakes.

Front 17

Earthquakes:

What is a normal fault?

Back 17

-hanging wall goes down relative to the footwall
-due to crustal stretching

Front 18

Earthquakes:

What is a reverse fault?

Back 18

-hanging wall goes up relative to the footwall
-due to crustal shortening
-slope (dip) of fault is steep

Front 19

Earthquakes:

What is a thrust fault?

Back 19

-hanging wall goes up relative to the footwall
-due to crustal shortening
-slope (dip) is not steep

Front 20

Earthquakes:

What is the Mercalli Intensity Scale?

Back 20

A scale designed to measure the degree of intensity of earthquakes, ranging from I for the lowest intensity to XII for the highest. The classifications are based on human perceptions

Front 21

Earthquakes:

How does faulting cause earthquakes?

Back 21

When stress is applied to a rock, it will bend but won't break until more stress is applied. Small fractures then occur and join together and then causes the rock to break in 2. Vibrations from the rock create an earthquake.

Front 22

Earthquakes:

What is a strike-slip behavior on pre-existing faults?

Back 22

Stick-slip behavior.When slipping takes place, bumps on fault generate vibrations. Alternations between stress buildup, when no slip occurs, and slip events (earthquakes).

Front 23

Earthquakes:

How is energy stored ahead of an earthquake?

Back 23

Energy is created when the breaking of a rock occurs either when a new fault initiates, or when protrusions on an existing fault break during sliding.

Front 24

Earthquakes:

How do P- and S- waves move?

Back 24

P-waves: move back & forth parallel to the direction in which the wave itself moves.

S-waves: move back & forth perpendicular to the direction in which the wave itself moves.

Front 25

Earthquakes:

Which wave moves faster? (P-or S-)

Back 25

P-waves

Front 26

Earthquakes:

Which wave cannot travel through liquid? (P- or S-)

Back 26

S-waves

Front 27

Earthquakes:

How do the different speeds of the P- and S- waves allow us to estimate quake locations?

Back 27

P-waves are felt about 2400 miles from the epicenter 4 minutes after the quake has started. S-waves are felt 12 minutes.

Front 28

Earthquakes:

What is the difference between comparing earthquake magnitudes and intensities?

Back 28

Magnitude estimates the amount of energy
released at the source of the earthquake.Intensity a measure of earthquake shaking
based on the amount of damage.

Front 29

Earthquakes:

Why use two different systems? (Mercalli Intensity Scale and the Richter Scale)

Back 29

The Mercalli scale shows you how much damage was done so you can picture it in your mind. The Richter scale tells you scientifically what happened. These numbers don't always match due to population of the area.

Front 30

Earthquakes:

How are earthquakes distributed as a result of plate tectonics?

Back 30

Divergent-Seismicity along mid-ocean ridges takes place at shallow depths.
Convergent- host intermediate and deep focus earthquakes.
Transform-have shallow focus (larger ones on land cause disaster)

Front 31

Earthquakes:

By what mechanisms do earthquakes cause damage?

Back 31

-ground shaking & displacement
-landslides
-sediment liquefaction
-fire
-tsunamis
-disease

Front 32

Earthquakes:

Why are R-waves so destructive?

Back 32

They are like ocean waves and have a rolling motion.

Front 33

Earthquakes:

How do we "predict" earthquakes?

Back 33

Long term predictions: based on two pieces of information: the identification of seismic zones and the recurrence interval (average time between successive events)
Short term predictions: detection of foreshocks, laser surveying of the ground, computer models of stress.

Front 34

Earthquakes:

What methods are used to estimate recurrence intervals and probabilities?

Back 34

Recurrence intervals: Examine sedimentary strata near a fault to find layers of sand volcanoes and disrupted bedding in the stratigraphic record.
Probabilities: use predictions

Front 35

Earthquakes:

Define stick-slip behavior

Back 35

Stop-start movement along a fault plane caused by friction, which prevents movement until stress builds up sufficiently.

Front 36

Earthquakes:

Describe the motions of the four types of seismic waves

Back 36

Compressional/P-waves: back and forth motion of coils.
Shear/S-waves: resemble waves in a rope.
L-waves: sideways like a snake
R-waves: like an ocean, rolling waves

Front 37

Earthquakes:

Explain how the vertical and horizontal components of an earthquake are detected on a seismograph.

Back 37

Horizontal waves represent time.
Vertical waves represent amplitude.
They are detected by vibrations moving a pen attached to a weight hanging from a spring.

Front 38

Earthquakes:

What is a Wadati-Benioff zone and why was it important to understanding place tectonics?

Back 38

A deep active seismic area in a subduction zone.
Intermediate and deep focus earthquakes happen partly in response to stresses caused by shear between the down going plate and the mantle.

Front 39

Earthquakes:

What is a tsunami and why does it form?

Back 39

When water from above the upthrust sea floor began moving outward from above the fault zone, a process that generated a series of giant waves.
Forms due to undersea earthquakes and large undersea landslides.

Front 40

Earthquakes:

Explain how liquefaction occurs in an earthquake and how it can cause damage.

Back 40

In beds of wet sand or silt, ground shaking causes the sediment grains to try and settle together. But because the spaces between grains are filled with water, this can't happen; instead, the water pressure in the pores increases and pushes the grains apart and the wet silt become a fluid-like slurry. Buildings can sink, mud fountains can occur, landslides can occur too.

Front 41

Earthquakes:

What types of structures are most prone to collapse in an earthquake? What types are most resistant to collapse?

Back 41

Most resistant- somewhat flexible, with strong supports, steel supported bridge columns, bolting bridge spans to columns.
Most prone to destruction- concrete block buildings, unreinforced concrete and brick buildings.

Front 42

Earthquakes:

What changes do rocks undergo during formation of a mountain belt?

Back 42

Deformation- a process by which rocks bend or break in response to compression, tension, or shearing.
Metamorphism and melting.

Front 43

Earthquakes:

What is the difference between brittle and ductile deformation?

Back 43

Brittle- breaking, shattering, cracking, and fracturing.
Ductile- objects change shape without visibly breaking.

Front 44

Earthquakes:

What factors determine whether a rock will behave in a brittle or ductile fashion?

Back 44

Brittle- many of the bonds break and stay broken, leading to the formation of a permanent crack across which material no longer connects.
Ductile- some bonds break but new ones quickly form. The atoms within grains rearrange, and change shape without any cracks forming.

Front 45

Earthquakes:

How are stress and strain different?

Back 45

Stress- an applied force that tends to deform a body (generates strain)
Strain- describes the change in body length, volume, or shape compared to it's original size or shape (deformation)

Front 46

Earthquakes:

What distinguishes a fault from a joint?

Back 46

Joints- natural cracks in rocks that represent traces of natural cracks along which the rock broke during brittle deformation.
Faults- A fracture in the continuity of a rock formation caused by a shifting or dislodging of the earth's crust, in which adjacent surfaces are displaced relative to one another and parallel to the plane of fracture.

Front 47

Earthquakes:

What types of motions do normal, reverse, and transform faults display?

Back 47

Normal- pull apart
Reverse- squish together
Transform- side by side (lateral)

Front 48

Earthquakes:

How do you recognize faults in the field?

Back 48

Displacement- offset. Layers on side of the fault do not match the layers on the other side.

Front 49

Earthquakes:

What is an anticline?

Back 49

Folds that have an archlike shape in which the limbs dip away from the hinge.

Front 50

Earthquakes:

What is a syncline?

Back 50

Folds with a troughlike shape in which the limbs dip toward the hinge.

Front 51

Earthquakes:

What is a monocline?

Back 51

Folds that go the same direction.

Front 52

Earthquakes:

Describe the principle of isostasy.

Back 52

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

Front 53

Earthquakes:

How do mountains form on convergent boundaries?

Back 53

Along the margins of continental convergent plate boundaries, where oceanic lithosphere subducts beneath a continent, a continental volcanic arc forms, and compression between 2 plates causes a mountain range to rise.

Front 54

Earthquakes:

How do mountains form in continent-continent collisions?

Back 54

Once the oceanic lithosphere between 2 continents completely subducts, the continents themselves collide with eachother.

Front 55

Earthquakes:

How do mountains form in continental rifts?

Back 55

As rifting continues, stretching causes normal faulting in the brittle crust above. Movement on the normal faults drops down blocks of crust, producing deep, sediment-filled basins separated by narrow, elongate mountain ranges that contain tilted rocks.