8th Grade Science: Overview Earthquakes: Glencoe/McGraw-Hill

The ___________ scale is used to describe the amount of damage an earthquake causes.

Modified Mercalli

Describe the movement of particles caused by a P wave.

P waves cause particle movement by push and pull or compress and stress.

The point on the surface directly above the point which an earthquake occurs

epicenter

The point on the surface of Earth directly above the earthquake's focus.

epicenter

The breaking, tilting, and folding of rocks is called

elastic deformation (or simply deformation)

_______ waves cause the most destruction.

Surface

Isostasy

The balancing of the upward force of the mantle with the downward force of the crust.

Reviewing the picture, where does the energy created by an earthquake originate? In what direction does it travel?

The energy created by an earthquake originates at the focus and radiates outward from the fault in all directions like ripples on a pond.

Reviewing the picture, describe what relationship exists between the focus of an earthquake and the epicenter?

The focus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement. The epicenter is on the earth's surface directly above the focus.

The Richter scale measures the __________ of an earthquake.

intensity

A ____ is a large area of flat land that is raised high above sea level.

plateau

Forces cause sections of Earth's surface, called _____, to move.

plates

Kind of wave that causes particles in rocks to move back and forth in the same direction that the wave is traveling

primary wave

At a _______ fault, rocks above the fault surface move up and over the rocks below the fault surface.

reverse

The rocks above a ________ fault are forced up and over the rocks below the fault.

reverse

In a ________, the hanging wall moves up relative to the foot wall.

reverse fault

Which fault is pictured

rocks above the fault surface move up and over rocks below the fault surface

Which fault is pictured

rocks move past each other

The waves of energy that an earthquake produces.

seismic

Instrument that measures seismic waves

seismograph

Records ground movements caused by seismic waves as they move through the Earth

seismograph

_______ forces can cause strike-slip faults

shear

______ pushes rocks of the crust in two opposite horizontal directions.

shearing

To relieve the ____ caused by the plate movement, rocks tend to bend, compress, or stretch.

stress

_______ pushes and pulls on the earth's crust

stress

At a ________ fault, rocks move past each other.

strike-slip

The rocks on either side of a ________ fault move sideways past each other.

strike-slip

In a _______, blocks of rock slide horizontally past each other.

strike-slip fault, also known as a lateral fault

Wave that moves rock particles in a backward rolling motion and a side-to-side swaying motion

surface wave

The slowest seismic waves that produce the most severe ground movements

surface waves

A downward fold in a rock is called a ______.

syncline

_____ is stress that pulls on rocks of the crust.

tension

Which fault is pictured

tension pulling rock apart

Reviewing the picture, describe what relationship exists between the focus of an earthquake and a fault in the Earth's crust?

A fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture. Earthquakes occur on faults. The focus is the point within the Earth's crust where an earthquake begins on the fault.

Explain how the terms are related: seismograph, seismogram, seismologist, Richter scale

A seismograph is an instrument that measures and records details of earthquakes, such as force and duration. A seismogram is a record produced by a seismograph. Seismologists are Earth scientists, specialized in geophysics, who study the genesis and the propagation of seismic waves in geological materials. The Richter scale is a numerical scale for expressing the magnitude of an earthquake on the basis of seismograph oscillations. A semiologist studies the strength of seismic waves using the Richter scale on a seismogram the was made by a seismograph.

Explain how the terms are related: earthquake and tsunami

A tsunami is giant wave usually caused by an earthquake beneath the ocean floor.

Explain how the terms are related: Primary wave (P wave), Secondary wave (S wave), Surface wave (L wave)

All are seismic waves sent out during an earthquake. P waves travel fastest and are the first to arrive from the earthquake. The different S waves arrive after the P waves. The slowest (and latest to arrive on seismograms) are surface waves, such as the L wave.

Identify the type of stress pictured

Compression, Tension, or Shearing

Identify the types of stress pictured

Compression, Tension, or Shearing

Crust

Earth's rocky outermost layer.

Reviewing the picture, describe what relationship exists between the epicenter of an earthquake and a fault?

Earthquakes occur on faults. The earthquake begins at a point on the fault plane called the focus. The focus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement. The epicenter is the point on the surface directly above the focus.

An earthquake's ______ is the point on Earth's surface directly above the earthquake focus.

Epicenter

The rocks on either side of a _____________ move in different directions.

Fault

How do geologists locate the epicenter of an earthquake?

Geologists measure the difference between the arrival times of P waves and S waves at 3 or more seismographs. Using these differences, they determine the distance of the epicenter for each seismograph and of the distances as circles on a map. The epicenter is located where the 3 circles intersect.

How does isostasy explain this statement: rivers dump sediments to the ocean floor, thick heavy layers of sediments pile up, yet the depth of the ocean water remains essentially constant.

Isostasy is the balance of two forces: the downward force of the crust with the upward force of the mantle. As sediments accumulate, the oceanic crust floats/sinks a little lower into the mantle. Floating lower on the mantle balances out the accumulating sediments.

How does isostasy explain this statement: an area covered by a large ice cap sinks.

Isostasy is the balance of two forces: the downward force of the crust with the upward force of the mantle. The ice adds weight to the crust. The additional downward force causes the crust in this area to sink.

How does isostasy explain this statement: land areas once covered by ice sheets are slowly rising.

Isostasy is the balance of two forces: the downward force of the crust with the upward force of the mantle. The melting of the ice reduces the weight of material on the earth's crust, thus reducing the downward force of the crust. The force of the mantle using upward on the crust causes the land to rise.

Describe the movement of particles caused by L waves (surface waves)

L waves tumble while going side-to-side

Identify the type of fault pictured

Normal, Reverse (Thrust), or Strike-slip

In what order do the three types of seismic waves arrive at a seismograph?

P waves travel fastest, so would drive first, followed by S waves, and then surface waves.

______ waves are the fastest.

Primary

What kind of waves cause particles in rocks to move back and forth in the same direction?

Primary waves

Which type of seismic wave produces the most severe ground movements?

Rayleigh waves (which are a type of surface wave) produce the largest amplitude and so most severe ground movements during earthquakes. Surface waves produce the most severe ground movements. They produce movements similar to waves in the water, where the water's particles move in a pattern that is almost circular.

The ____________ scale is used to describe the strength of an earthquake.

Richter

A ______ forms when the block of land between two normal faults slides downward.

Rift Valley

Describe the movement of particles caused by an S wave.

S waves move rock particles up and down, side-to-side, or at 90 degree angle.

Kind of wave that causes particles in rocks to move at right angles to the direction of the wave

Secondary wave

What kind of waves cause particles in rocks to move at right angles to the direction of the wave?

Secondary waves

When an earthquake occurs, energy is released in the form of ______.

Seismic waves

What are seismic waves?

Seismic waves are vibrations that travel through Earth carrying the energy released during an earthquake

What kind of waves are responsible for all the damage an earthquake causes?

Seismic waves called Surface Waves

At the very center of Earth is a _____________.

Solid dense inner core

Mantle

The layer of the earth that extends from the bottom of the crust to the core.

Describe the moment magnitude scale, and explain why it is useful in measuring earthquakes.

The moment magnitude scale provides an estimate of the total energy released by an earthquake. It can be used to rate earthquakes of all sizes, regardless of whether they occur close by or far away.

Explain how the terms are related: focus and epicenter

The point beneath the earth's surface where rocks break and move is called the focus of an earthquake. The point directly above the focus of an earthquake on the earths surface is called the epicenter.

Explain how the terms are related: seismic wave and earthquake

Waves of energy produced by an earthquake are called seismic waves.

An upward fold in a rock is called an ______.

anticline

At a reverse fault, _________ forces pushes on rocks from opposite directions.

compression

______ is stress that squeezes the rocks of the crust.

compression

An earthquake that measured X on the modified Mercalli scale would cause ____________ damage.

considerable

The outermost layer, or surface, of the earth is called the _________.

crust

A rounded hill usher up by rising magma is called a __________.

dome

At a normal fault, rock above the fault surface moves ______ in relation to rock below the fault surface.

downward

An _____ is the vibrations produced by the breaking of rock

earthquake

Vibrations produced by the breaking of rock

earthquake

When rocks are stressed beyond their _______ limit they break, move along the fault, and return to their original shapes.

elastic

A break or a crack along which rocks move is call a

fault

Mountains formed by blocks of rock uplifted by normal faults are called _______.

fault block mountains

When rocks break they move along surfaces called ___

faults

The point beneath Earth's surface at which rock under stress breaks and triggers an earthquake

focus

The point where rocks break and release energy in the form of seismic waves

focus

A bend in a rock is called a _________.

fold

The block of rock below a fault is called the

foot wall

Reverse fault diagram

foot wall lower than hanging wall

Normal fault diagram

foot wall up, hanging wall lower

A crack in a rock is called a

fracture

The block of rock above a fault is called the

hanging wall

When the soil becomes more liquid

liquefaction

A measure of the energy released by an earthquake

magnitude

Earth's largest layer is the _________.

mantle

At a ______ fault, tension pulls rocks apart.

normal

In a _______, the hanging wall moves down relative to the foot wall.

normal fault

In a ______, the hanging wall slides over the foot wall.

thrust fault

Ocean wave caused by an earthquake

tsunami

Suppose water along a shoreline moves rapidly toward the sea, exposing a large portion of land that is usually under the water. This is a clue that a ___________ might strike.

tsunami