Earthquakes

Which of the following are true? Check all that apply.

- The footwall block moves down relative to the hanging-wall block for a reverse fault. - the footwall block underlies a fault - Stress builds up on a fault during the "stick" phase of stick-slip behavior.

Which of the following are elastic? Check all that apply.

- the up-and-down and/or side-to-side movement of the ground surface during the passage of a seismic wave - the warping of rocks adjacent to a fault prior to movement on the fault - the compression of a spring below a critical level of stress

Body waves can be further divided into

1) Compressional (P) waves 2) Shear (S) Waves

Earthquakes and other sources of vibration in the Earth (explosions, rock falls etc.) produce waves that

1) Go through the volume of the Earth, called Body Waves 2) Go along the surface of the Earth, called Surface Waves

dip-slip fault

A fault in which the movement is parallel to the dip of the fault. the dominant motion involves moving up or down the dipping (tilting) fault plane. rock above the fault - hanging wall or headwall rock beneath - footwall

A seismogram is

A graph record of the ground motion

A seismograph is

A seismometer connected to a seismograph to produce a record of ground motion

sag ponds

A typical attribute of the strike-slip fault, linear shallow ravines called sag ponds follow their trace

Which of the following terms does not belong with the others?

A. surface waves B. love waves C. rayleigh waves D. p-waves The correct answer is P-waves

rupture

An episode of slip on a fault

A seismometer is

An instrument that detects the motion of the ground

What can and cannot transmit P and S waves?

Can: Solid objects (metals, rocks, ice) Cannot: Liquids and gases do not have a definite shape (that is, they have no shear strength

What causes volcanic earthquakes?

Earthquake produced by landslide or lahar or pyroclastic flow Earthquake produced by magma migration or bubbling Earthquake produced by fault movement caused by weight of volcano Earthquake produced by volcanic explosion (blast)

slip

If a fault yields to external stress, and the motion of rocks on two sides of it is fast

Fault fracture

If rocks on one side of the break shift relative to rocks on the other side

reactivated faults

If stress develops in the area again, the weakest spot is going to be along preexisting inactive faults, and that is where new movement is most likely to occur.

creep

If the motion is so slow that no seismic waves are generated

joint fracture

If there is no movement of one side relative to the other, and if there are many other fractures with the same orientation

Two types of surface waves

Love waves and Rayleigh waves

Which of the following seismic waves travel the fastest?

P-waves

A left-lateral strike-slip fault trends East-West. Which of the following quadrants are compressional? Select all that apply.

SE, NW

A right-lateral strike-slip fault trends East-West. Which of the following quadrants are dilatational? Select all that apply.

SE, NW

A right-lateral strike-slip fault trends East-West. Which of the following quadrants are compressional? Select all that apply.

SW, NE

elastic deformation

Stress (or pressure) is force per unit area Higher stress produces higher strain region where the material will return to its original shape when the stress is removed

Three types of stress

Tensional stress (pulling apart), compressional stress (pushing together) shear stress (one side moves past the other horizontally)

Fermat's Principle

The principle states that the path taken by a ray of light between any two points in a system is always the path that takes the least time. This is why seismic waves are curved

fracture

When rocks break in response to stress, it is the resulting break

Seismograph

a device that measures the strength of an earthquake seismometer plus recording device records vibrations of the Earth, especially earthquakes. Seismograph generally refers to the seismometer and a recording device as a single unit

inactive fault

a plane or a zone separating different rocks, but with no evidence for recent activity.

active fault

a structure that shows recent movement (e.g., a stream is offset).

waves

a traveling disturbance that carries energy, but does not transport matter

Surface waves

a type of seismic wave that forms when P waves and S waves reach Earth's surface waves that move close to or on the outside surface of the Earth rather than through the deep interior like the faster P or S waves. Two principal types of surface waves, Love and Rayleigh waves, are generated during an earthquakes. Rayleigh waves cause both vertical and horizontal ground motion, and Love waves cause horizontal motion only. They both produce ground shaking at the Earth's surface but very little motion deep in the Earth. Because the amplitude of surface waves diminishes less rapidly with distance than the amplitude of P or S waves, surface waves are often the most important component of ground shaking far from the earthquake source.

Where do earthquakes occur?

along plate boundaries and preferentially within narrow regions known as seismic belts

Basin and Range

an example of an extensive normal fault system

The current understanding of the way earthquakes happen...

based on the recognition that Earth's crust contains narrow zones of weakness, termed faults, that allow large masses of rock forming the crust to move relative to each other. In many respects, faults are simply very large cracks in the otherwise solid Earth's crust.

Hanging-wall (HW) block

block above fault

Footwall (FW) block

block below fault

faults

breaks (fractures) along which one side slides past other side

What is triangulation?

can be used to locate an earthquake with seismometers

Reverse fault

caused by compression block above fault (hanging-wall block) moves up relative to block below fault (footwall block) This requires side view (cross-section view) pushes the hanging wall up relative to the footwall. Reverse faults shorten and thicken the crust results in duplication of rock units and thickening • 3 sectors • Central compressional sector • Both arcs (sector boundaries) have same trend

oblique-slip fault

caused by shearing and tensional stress A fault with both strike-slip and dip-slip components. combines elements of strike-slip faults with normal or reverse faults

Strike-slip fault

caused by shearing stress a type of fault where rocks on either side move past each other sideways with little up or down motion (pass each other) fault motion is entirely horizontal (no up or down) and is only observed in top views (map views) also form fault zones 4 equal-sized sectors • Sector boundaries are two perpendicular lines

Normal fault

caused by tension block above fault (hanging-wall block) moves down relative to block below fault (footwall block) This requires side view (cross-section view). crust undergoes extension 3 sectors • Central dilatational sector • Both arcs (sector boundaries) have same trend

ductile deformation

continuous deformation; no fractures present more likely where temperatures and pressures are high

Which type of plate boundary is associated with a deep-sea trench?

convergent

The thinnest of Earth's layers is the __

crust

The lithospheric plates are composed of the ___.

crust and the asthenosphere

Horst Fault

development of two reverse faults causing a block of rock to be pushed up

Brittle deformation is

discontinuous deformation

At which type of plate boundary is new lithosphere added?

divergent

Which type of plate boundary involves plates that move apart?

divergent

A seismic ray with a dilatational first motion produces a(n) ____ deflection on a seismogram, and a seismic ray with a compressional first arrival produces a(n) ___ deflection.

downward; upward

Rocks behave as ___ material near the Earth's surface

elastic

Ductile deformation is mostly associated with low temperature and low pressure.

false

Left-lateral, left-handed, sinistral

far block (opposite) moves to left relative to near block

Right-lateral, right-handed, dextral

far block (opposite) moves to right relative to near block

fault zone

formed when a region undergoes tension or compression, those stresses tend to be spread out over a number of different faults

Concept of elastic rebound background

formulated by H.F. Reid, a member of the "State Earthquake Investigation Commission". The commission studied the effects of the 1906 San Francisco earthquake, and made some key observations of the lands deformed by the earthquake,

Snell's Law

governs how waves go through (refract) and/or bounce off (reflect) boundaries between materials with different properties.

material is called elastic if

if it will recover its original shape after it has been deformed (strained) by a force (stress).

Permenant Deformation

if we strain spring too much, it will not return to original shape when stress is removed • Some deformation is permanent • Stress at which deformation starts to become permanent is known as yield strength or elastic limit

Seisometer

instrument that can measure passage of seismic waves can detect waves emitted by even the smallest earthquakes can register faint vibrations in the ground

deformation

involves change in position, change in orientation, change insize, and change in shape

Earthquakes

involves sudden release of energy, most commonly produced by movement along faults (surfaces along which one side of rock moves relative to the other side).

Graben Fault

is a depressed block of the Earth's crust bordered by parallel faults

joint set

joints with a common orientation

Epicenter

location on ground surface directly above hypocenter

exfoliation joints

make the rock appear to be flaking off in sheets, occurs when a body of rock expands in response to reduced pressure, such as when overlying rocks have been removed by erosion.

What is the largest, most voluminous part of the Earth?

mantle

What causes earthquakes?

movement of plates Motion along new or existing faults Volcanic eruptions Landslides Meteorite impacts Nuclear detonations

Where a region is under tensional stress ____ is likely to occur

normal faulting

What type of faults are divergent?

normal faults

half-graben

occur where slices (fault blocks) with normal faults on one side "slide" downwards. Alternatively, where the rocks are more rigid, a series of horsts (hills) and grabens (valleys) will form

fault scarp

offset of earth's surface produced by movement along fault during earthquake

plastic deformation

permanent change in shape by bending and folding

Shear (S) waves

propagate as distortions of shape, but do not cause significant changes in volume

Compressional (P) Waves

propagate as pulses of compression, i.e. they change the volume of material through which they go

What type of faults are convergent?

reverse faults

strike-slip fault examples

san andreas fault or the Anatolian Fault of Turkey. The North Anatolian Fault marks part of the complex boundary between the Eurasian, Arabian, and African Plates. It has been responsible for many deadly earthquakes, and threatens major cities including Istanbul.

Body waves

seismic waves that travel through the Earth's interior waves that move within the Earth's interior or within a body of rock. P and S waves are body waves.

Hooke's Law

states that the strain is directly proportional to stress. Earth's surface rocks will follow this law if stressed (strained by a force).

What causes faults to develop?

stress

elastic rebound theory continued

stress builds up, rock bends, reaches critical value,and then breaks and moves suddenly while unbending, releasing energy as seismic waves radiating outward from rupture location

Rayleigh waves

surface waves that move in an elliptical motion, producing both a vertical and horizontal component of motion in the direction of wave propagation

Love waves

surface waves that move parallel to the Earth's surface and perpendicular to the direction of wave propagation.

brittle deformation

the cracking and fracturing of a material subjected to stress discontinuous deformation; fractures / cracks are present more likely where temperatures and pressures are low

amplitude

the maximum disturbance or distance from the constant point. On a seismogram the horizontal time line is flat until there is a ground disturbance which is recorded as wave, or seismogram. The amplitude of a seismic wave is the amount the ground moves up or down. Amplitude is one-half the distance between the crest and trough of one wave length Height of a waves crest

S waves continued

the primary body wave; the first seismic wave detected by seismographs; able to move through both liquid and solid rock..Also called compressional or longitudinal waves, they compress and expand (oscillate) the ground back and forth in the direction of travel, like sound waves that move back and forth as the waves travel from source to receiver. P wave is the

P Waves continued

the primary body wave; the first seismic wave detected by seismographs; able to move through both liquid and solid rock..Also called compressional or longitudinal waves, they compress and expand (oscillate) the ground back and forth in the direction of travel, like sound waves that move back and forth as the waves travel from source to receiver. P wave is the fastest wave

Seismogram

the record of an earthquake's seismic waves produced by a seismograph set of wiggles recorded by seismograph. • Seismic waves would arrive first at location 1 and later at location 2, which is farther from hypocenter. A real-time record of earthquake ground motion recorded by a seismograph. Seismograms are the records (paper copy or computer image) used to calculate the location and magnitude of an earthquake..

fault rupture

the sudden displacement of rocks on either side of a fault that begins at the focus and spreads out across the fault

Hypocenter (focus)

the underground focus point of an earthquake. location where disturbance originates; it is from here that seismic waves radiate outward.

elastic rebound theory

theory that rocks that are strained past a certain point will fracture and spring back to their original shape if a volume of rock experiences stress that is acting to deform it, it will initially change shape (strain), and eventually will reach the strength limit and break. Some pre-existing zone of weakness is likely to yield first. These zones of weakness in the Earth's crust are known as faults.

Continental crust is thicker and less dense than oceanic crust

true

The average rate of movement of Earth's tectonic plates is

up to 15 cm per year

seisimic waves

vibrations that travel through Earth carrying the energy released during an earthquake Energy moves outward as expanding sphere of waves

seismic waves

vibrations that travel through Earth carrying the energy released during an earthquake Propagation of waves outward from the source may be described by a wavefront. Alternatively, it may be described by rays.

When does an earthquake occur?

when sudden movement along a fracture (break or crack)releases energy that radiates outward from the point of rupture as a series of waves that temporarily cause shaking of Earth's surface The shaking is not the earthquake; the earthquake is the event that caused the waves, which cause the shaking.

nucleation point and origin time

where and when the rupture starts

magnitude

• Intensity of quake is known as magnitude. All other things being equal, larger quake would produce taller wiggles on seismogram.