Geology Exam 3

What is an earthquake?

Vibrations of Earth produced by the raped release of energy.

How do Surface (L) waves travel?

When P and S waves reach the surface of Earth some of their energy is transformed into Surface (L) waves.

How many 6.0 earthquakes would it take to release the same amount of energy as one 8.0 earthquake?

1,000

What two statements below are correct?

1.) A 7.0 magnitude quake is roughly 32 times more energy than a 6.0 2.) A 7.0 magnitude quake is roughly 1,000 times more energy than a 5.0

What statements are correct regarding seismograph units?

1.) A seismograph instrument works based on the principle of inertia 2.) The seismograph unit must be mounted to solid bedrock

Which four answers below may be used to aid in short-range earthquake prediction?

1.) Animal Behavior 2.) Change in ground elevation 3.) Changes in groundwater levels 4.) Foreshocks

Which three statements below help to explain why fires after an earthquake are a concern in populated areas?

1.) Gas lines may rupture during earthquakes 2.) Water lines may rupture during earthquakes 3.) Electrical lines may be severed during earthquakes

What four statements are true about most earthquakes?

1.) Most earthquakes around the Pacific happen at convergent boundaries 2.) When the energy becomes too great, the crust slips along a fault 3.) Most earthquakes can be explained by the elastic rebound theory 4.) Most earthquake activity occurs along the circum-Pacific belt

What three statements are true regarding earthquakes?

1.) Most earthquakes happen along faults 2.) Energy from an earthquake radiates out in all directions 3.) The epicenter is located on the earth's surface directly above the focus.

Which four statements below are true regarding a tsunami?

1.) Most tsunami result from the rapid displacement of the seafloor along an underwater fault zone 2.) A possible warning of a tsunami is the rapid withdrawal of water from the beaches 3.) A tsunami slows and gain height as it nears land 4.) Tsunami are often associated with fault slip along a subduction zone

What three statements are true regarding P-waves?

1.) P-waves travel the fastest of all earthquake waves 2.) P-waves travel by compressing rocks 3.) P-waves travel around 6 kilometers per second (14,000 miles per hour) through crustal granite

What three statements below are true about the study of earthquakes?

1.) Seismology is the study of earthquakes 2.) Seismographs are instruments used to record earthquakes 3.) Seismographs work based on the principle of inertia.

What four statements are true regarding the San Andreas Fault?

1.) The San Andreas Fault is located in California and mostly separates the North American Plate from the Pacific Plate 2.) The central segment of the fault (located south of San Francisco) creeps along resulting in little to no major seismic activity 3.) The southernmost section of the fault is a seismic gap and may be where the next "Big One" will occur 4.) The San Francisco Bay area has a long-range forecast of a 62% probability of a 6.7 or greater magnitude earthquake by the year 2032.

Liquefaction is likely to occur during an earthquake in areas where:

1.) The Sediments are unconsolidated 2.) The ground is saturated

What four statements are true of S-waves?

1.) They can travel through the body of the earth 2.) They can produce up-and-down and sideways motion of the earth 3.) P-waves travel about 1.7 faster than an S-wave 4.) S-waves cannot travel through liquids

What three statements are true regarding surface waves?

1.) They travel slower than P and S-waves 2.) They may have an up and down or side to side motion 3.) They typically cause the most amount of damage.

Which three statements are true regarding this image? Look at question 14 quiz 7

1.) This image is showing regions of earthquake intensity as defined by the Modified Mercalli Scale 2.) Around the epicenter damage was only slight in specially designed structures 3.) Around the epicenter damage was great in poorly built structures

How much larger is the amplitude (shaking) of an 8.0 earthquake compared to a 5.0?

1000

How many 5.0 earthquakes would it take to release the energy of one 7.0 earthquake? What about 9.0 earthquakes?

1000 and 100,000

How much more energy is released from an 8.0 earthquake than from a 5.0?

32,000

What are foreshocks?

A foreshock is a mild tremor preceding the vident shaking movement of an earthquake.

What are seismic waves?

A general term encompassing all waves generated by an earthquake. They are generated by the sudden slippage results in the shaking.

What is a tsunami?

A large sea wave that is usually produced by an earthquake, but can also result from submarine landslides and volcanic eruptions.

Are there ever any warning signs a tsunami is approaching?

A warning can be the sudden withdrawal of the sea.

Describe the asthenosphere

A weak zone. Convection within this soft asthenosphere is thought to be the driving force of plate motion. It is roughly 100km to 410 km deep.

These are caused by adjustments in the crust after a large earthquake........

Aftershocks

What are aftershocks?

Aftershocks are continuing adjustments along a fault that may generate a series of earthquakes.

Measurement of how intensely the ground shook during an earthquake (measured on seismogram)

Amplitude

What is a seismograph?

An instument used to record earthquakes. This helps seismograph by isolating a heavy weight fromthe rest of the earth.

Soft rock zone located from about 100 km to 660 km below Earth's surface

Asthenosphere

Discuss the theory on how the earth became layered?

Gravity produced the contracting and accretion (the coming together) of the nebular dust and gases. The heat generated, along with heat from radioactive decay produced (near) melting. The melting allowed differention (the separation of a mixture into distinct parts) as the heavier elements sank to the core and the lighter elements floated "to the top"

The time lag between the first arrival of the P-wave and first arrival of the S-wave can be used to determine:

How far away the earthquake was from the seismic station

How does a seismologist locate the epicenter of an earthquake? Seismograms from how many stations are needed?

If the P-S time intervals are known fromat least three seismograph stations, then the epicenter of any earthquake can be determined.

Zone comprised predominantly of solid iron

Inner Core

What is intensity of an earthquake?

Intensity is a subjective or qualitative measure of the kind of damage done by an earthquake as well as peoples reaction to it.

What is liquefaction?

It is a saturated soil due to the inability of water to compact.

Describe the Modified Mercalli Intensity Scale.

It is a scale with values from 1 to 12 used to characterize earthquakes based on damage.

What is the Moho?

It is a seismic discontinuity between the crust and the mantle.

Describe the amplitude of L waves compared to the body waves?

It is generally more severe resulting in more damage

Describe the S-wave shadow zone

It is the result of S-waves not being able to travel through the liquid outer core. It incorporates the same area as the P-wave shadow zone (the ring) plus the area inside the ring

Describe the P-wave shadow zone.

It is the result of the large refraction when a P-wave enters the liquid outer core. It forms a ring around Earth's on the opposite side of Earth from wherever the Earthquake occurred.

What is the continental crust?

It is thicker, less dense, and felsic to intermediate in composition. It primarily forms at a subduction zone.

This phenomenon may occur in saturated unconsolidated materials during an earthquake

Liquefaction

What type of material can S-waves NOT travel through?

Liquids and Gases

Richter scale unit used to describe the size of an earthquake

Magnitude

12-level scale used to describe earthquake intensity

Modified Mercalli

Boundary located between the mantle and crust

Moho

What is the oceanic crust?

It is thinner, more dense, and mafic in composition and forms from the partial melting of the upper mantle primarily at spreading centers.

Fastest seismic wave

Primary

Scale used to estimate energy released based upon maximum amplitude and distance from epicenter e.g. 6.3

Richter

Famous fault that runs through much of California

San Andreas

Shear body wave that cannot travel through liquids

Secondary

Quiet zones along a fault that are storing energy for future quakes

Seismic gap

What is the current status with earthquake prediction?

Seismic gaps can help us predict where the next earthquake may strike, but does not tell us when.

Why do seismic waves travel in a curved path through the Earth?

Seismic waves increase in velocity as they enter more dense material with depth. Multiple retractions is why there are curved path.

What are seismic gaps?

Seismically quiet regions where stress is (apparently) building

Record obtained from a seismograph

Seismogram

Instruments that record seismic waves

Seismographs

The study of earthquake waves

Seismology

What is the geothermal gradient/

Shows that Earth's temperature increase with depth.

These seismic waves are the most destructive and are referred to as L-waves

Surface

What is this map showing? Question 20 quiz 7

The amplitude of seismic waves increases in soft mud

What causes magnetic reversals?

The curie point

What information can be derived from the time interval between the first arrival of the P-waves and the first arrival of the S-wave on a single seismogram?

The distance in time between the first arrival of the P-wave and the first arrival of the S wave at any given seismic stations is proportional to the distance between the earthquaked epicenter and the seismic station.

What information can be derived from the time interval between the first arrival of the P and S waves, and the maximum amplitude recorded on a single seismogram?

The energy released or the magnitude.

These large water waves are often generated by earthquakes occuring under the ocean

Tsunami

How do P-waves travel?

They travel by compression through Earth. They travel through crustal granite at about 6 km/s (13,000 mph)

How fast do S-waves travel compared to other seismic waves?

They travel slower P-waves but faster than surface waves. They only travel through solids.

How fast do L waves travel compared to other seismic waves?

They travel slower than P and S waves

How do S-waves travel?

They travel through Earth by a shearing motion. They travel through crustal granite at about 3.6 km/s (8,000 mph)

Minimum number of seismic readings necessary to locate the epicenter of an earthquake

Three

Theory used to explain the behavior of rocks in relation to how they generate earthquakes

Elastic Rebound

Point on Earth's surface directly above the focus

Epicenter

Due to new technologies, most earthquakes are successfully predicted 48 hours before they occur. True or False

False

Seismic gaps are regions along a fault where earthquake activity never occurs. True or False

False

Fracture in earth's crust where earthquakes may occur

Fault

What is a fault creep?

Fault creep is the name for the slow, constant slippage that can occur on some active faults without there being an earthquake.

Location on a fault where energy is released causing an earthquake

Focus

What is the difference between the focus (hypocenter) and epicenter of an earthquake?

Focus is the original point of rupture along a fault. The epicenter is the surface point directly above the focus.

Moment magnitude is best used for describing very large earthquakes. True or False

True

Belt of most of the world's seismic activity (hyphenated words)

Circum-Pacific

Most earthquake activity occurs along what belt?

Circum-Pacific Belt

This crust is lighter in color, less dense, and thicker than the other type of crust

Continental

This is the main way heat travels through the mantle

Convection

What is the difference between convection and conduction?

Convection is the driving force of plate motion. it is also believed that convection within the outer core is responsible for creating Earth's magnetic field

Where is Earth's magnetic field created?

Convection within the outer core is responsible for creating Earth's magnetic field.

Because of multiple retractions seismic waves take this type a path through the earth.

Curved

What are seismic discontinuities?

Distinct seismic boundaries (largely defining the layers of the Earth) are referred to as seismic discontinuities.

What type of plate boundary has shallow, intermediate, and deep-seated earthquake activity?

Divergent, Convergent, and Transform

A vibration of earth produced by the rapid release of energy

Earthquake

What is the relationship between earthquake magnitude and yearly occurrence within that magnitude range?

The larger the earthquake magnitude the less it occurs during the year.

What is the magnitude of an earthquake?

The magnitude of an earthquake is determined by the amplitude of the shaking and the distance to the epicenter.

How does a seismograph work based upon inertia?

The principle of inertia says that an item at rest will stay at rest until an outside force is acted upon it.

Why are fires often associated with earthquakes in populated areas?

The shaking of the earthquake severed many of the electrical and gas lines.

What is seismology?

The study of earthquakes.

How are the inner and outer cores similar? How are they different?

They are both computationally the same, both composed predominantly of iron, however, physically the inner core is a solid while the outer core is liquid. Even though thte inner core is hotter than the outer core, it is solid due to the higher pressure, with greater depth. Early in Earths history there was no inner core (all the core was molten) but as Earth loses heat the molten iron solidifies and sinks to the center forming the solid inner core.

How fast do P-waves travel compared to other seismic waves?

They are the fastest seismic waves and one that can travel through solids, liquids, and gases.

Why are tsunamis so dangerous?

They can travel across an entire ocean and cause devastation far from its source.

Can earthquakes be predicted with reliability?

They cannot be predicted with reliability.