ATM OCN 140 - Earthquakes Unit

Acceleration during an earthquake is usually measured relative to ____

Acceleration due to gravity

The Richter magnitude scale uses the ______ of seismic waves to determine the amount of shaking and thus the size of an earthquake

Amplitude

Big earthquakes do not happen every year in the United States, but their cumulative financial effects are forecast using ____

Annualized earthquake losses

The decrease in velocity of both P and S waves at about 100 km depth marks the top of the ____

Asthenosphere

The damage done to this house was most likely due to ____

Horizontal ground movement

Better understanding of fault movements largely comes from ____

Improvements to field equipment and instrumentation

In general, earthquake ____ decreases with distance from the epicenter

Intensity

Why is the USGS Did You Feel It program so important?

It allows for the quick collection and dissemination of useful data concerning shaking during earthquakes

What does the word slip refer to when used to describe earthquakes?

It means movement has occurred along a fault

Why is the Richter magnitude scale less reliable for large earthquakes that occur far away?

It uses short-period seismic waves

The next major movement along the Hayward fault is projected to ____

Last about 22 seconds and have about 2 meters of slip along 13 km of fault

Which law of physical geology can be used to determine that these rock layers were deformed into folds after they were deposited?

Law of original horizontality

Earthquake magnitude is strongly influenced by the ____

Length of the fault rupture

What tectonic action has occurred in western North American over the last 5.5 million years that is responsible for the earthquakes in central and southern California?

The Gulf of California has opened up in a rifting action that has caused the land west of the San Andreas fault to attach to the Pacific plate

How did the Nazca plate move with respect to the South American plate to cause the largest earthquake ever recorded?

The Nazca plate moved eastward and downward beneath the South American plate, causing ruptures along a long and wide stretch of subduction zone

Charles Richter based his earthquake magnitude scale on the idea that ____

The bigger the earthquake, the greater the shaking of the Earth

First recognized by J. Tuzo Wilson in 1965, ____ faults are a special type of horizontal-movement fault that connects the ends of two offset segments of plate edges

Transform

What kind of fault is shown here?

Transform

True or false: The greater the magnitude of an earthquake, the greater the intensity

True

True or false: every single US state has experienced earthquakes

True

Which building is likely to have the longest period?

A 35-story skyscraper

What is a strike-slip fault?

A fault where the slip is predominantly horizontal and parallel to the fault plane

Why are powerful earthquakes projected to hit Mexico City in the near future?

A large seismic gap exists along a nearby subduction zone

What caused the large tsunami that struck Indonesia on 26 December 2004?

A long (1,500 km) fault rupture at a convergent plate boundary where a plate is being subducted

Without a detailed working theory on the behavior of faults, it appears that we may never be able to determine ____

A method of short term earthquake prediction

The largest earthquake ever recorded was caused by ____

A rupture along the Nazca plate as it was converging with the South American plate

To study earthquakes, seismologists must record the movement of earthquake waves in ____ directions

Three

The block above the fault plane in this image is referred to as the ____

Hanging wall

Similar to sound waves passing through a trombone, the shorter the rupture length along a fault the ____ the frequency of the seismic waves that are generated

Higher

An earthquake occurs along a south-moving fault. According to the process of directivity, the largest amount of energy should be directed to the ____

South because more energy is sent in the direction of fault movement

The acceleration due to gravity is ____, which is referred to as 1.0 g

The 9.8 m/sec squared

A fault-rupture length of 10 km produces approximately a magnitude ____

6

In eastern North America, large earthquakes ____

-Lack significant recent faulting -Are associated with low-strain regions -Mostly occur at the sites of failed rifts

What describes a Primary Wave?

-Moves in a push-pull fashion -The first to reach a recording station -Can travel through any material

What statements accurately describe the 1964 earthquake event in Alaska?

-The earthquake had a magnitude of 9.2 -The ground shook for a long time, causing many mass-wasting events and a large tsunami -It occurred on Good Friday, 27 March

Order the steps involved in the tectonic history of North America with respect to the Pacific Ocean basin

-The opening and widening of the Atlantic pushes North America westward -Subduction of Pacific Ocean crust occurs along the west coast -North America collides with spreading centers in the Pacific Ocean near Los Angeles -A transform fault, the ancestor of the San Andreas fault, connects spreading centers to the north and south of LA

The 1964 earthquake in Alaska was very powerful, yet the loss of human life was not as high as it could have been. What factors helped to limit the loss of life?

-The tsunami struck when the tides were low -Above average temperatures helped to prevent cold-related deaths as heating systems were being repaired -Relatively few people lived in the area at that time of the year

What are the problems posed by the widespread use of concrete floor slabs in Haiti?

-They are heavy -They are supported by flimsy concrete columns that fail in earthquakes -They are weak in earthquakes

The two largest New Madrid earthquakes occurred in the years ____ and ____

1811 and 1812

How many states in the US have experienced earthquakes?

50

Seismic waves that pass through the interior of the planet are called ____ waves, whereas those that travel across the surface are called ____ waves

Body; surface

How do scientists identify the depth to the top of the asthenosphere in the Earth's interior?

Both P and S waves slow down

How is earthquake magnitude measured?

By analyzing the seismic wave traces on a seismogram

The first Great Shakeout Event was held in ____ to help prepare residents for the next large earthquake

California

In terms of characteristic, earthquakes of eastern North America most closely resemble those that occur in ____

Central North America

Movements occur in succession for several years and then do not occur again for decades or centuries describes ____

Clustered type of fault movements

A building constructed of ____ is likely to have a shorter period

Concrete

Tectonic plates collide due to ____ motions, move away from each other due to ____ motions, and slide past one another at transform faults

Convergent; divergent

The USGS has developed a program called ____ that encourages people to report shaking experiences to better measure Mercalli Intensity of earthquakes

Did You Feel It?

Geologists measure the orientation of tilted rock layers. ____ is the angle of inclinations from the horizontal of a tilted rock layer, and ____ is the compass bearing of a rock layer where it pierces the horizontal plane

Dip; strike

When a rupture moves along a fault, it tends to send more energy in the direction it is moving. The phenomenon is called ____

Directivity

What is the cause of the tectonic stress that results in earthquakes in Turkey?

Due to the northward movement of the Arabian plate into Eurasia, Turkey is being rotates and moved westward in what is called escape tectonics

Why are scientists predicting a large earthquake for the Pacific Northwest of the United States?

The Cascadia subduction zone occurs there and appears to be overdue for a large earthquake

A(n) ____ is the vibrations we feel when sudden movement occurs along a fault

Earthquake

The August 2011, 5.8 earthquake along the ____ of the United States took people by surprise when it shook the ground and caused building damage in New York and Washington DC

East Coast

Which of the following statements best describes elastic rebound theory?

Energy builds up as elastic strain in rocks. When the applied stresses become overpowering, the rocks at the fault rupture

Despite being located away from active plate edges, the "stable" central and eastern United States is home to clusters of ____

Epicenters

A rift that starts to rip a continent apart but then stops before the continent split is a(n) ____

Failed rift

True or false: earthquake early warning systems can predict when an earthquake will occur with a great accuracy

False

True or false: the central US is the only region of the country that is not threatened by earthquakes

False

Our understanding of how ____ movements work is continually being advanced through field equipment and instrumentation improvements

Faults

The block below the fault plane in this image is referred to as the ____

Foot wall

Smaller earthquakes that precede the main shock are called ____, and those that follow the main shock are called ____

Foreshock; aftershock

The number of waves passing a given point during one second is referred to as ____

Frequency

According to elastic-rebound theory, rocks do not constantly move in response to stress because their rough and irregular surfaces generate ____ that retards movement

Friction

Surface waves are referred to as ______ waves because they take more time to complete one cycle of motion and are the slowest moving

Long

Our ability to forecast earthquakes on a(n) ____ term timescale is fairly good, but we have no ability to predict earthquakes on ____ term timescales

Long; Short

The location of the epicenter and hypocenter of an earthquake can be determined by ____

Looking at the difference in arrival times of different types of seismic waves

Similar to a rupturing fault, when the path of sound waves through a trombone is extended the frequency is _____ and the tone is lower

Lower

_____ is a measure of the amount of energy released during an earthquake

Magnitude

The largest earthquake in a series that occurs on the same portion of a fault is called the ____

Main shock

The ____ scale is a descriptive scale based upon the effects of an earthquake on people and buildings

Mercalli Intensity

Why is it of greater concern to design buildings to withstand horizontal ground movement than to design them to withstand vertical ground movement?

Most buildings are already designed to handle the vertical forces associated with their own weight

From 1811 to 1812, the ____ earthquakes occurred in quick succession and numbered in the thousands, with several measuring 7-plus in magnitude

New Madrid

The Richter magnitude scale is only useful for assessing earthquakes that ____

Occur nearby and are moderate in size

The 2002 Denali earthquake is very similar in its characteristics to the hypothetical California earthquake scenario, with one major exception: the Denali earthquake ____

Occurred in a remote area, while the California earthquake will directly affect millions of people

An analysis of earthquake probabilities suggests that it is most likely that the next major California earthquake will occur ____

On the southern San Andreas fault

The majority of earthquake hazards in the US are connected to ____

Ongoing subduction along the west coast of North America

The law of ____ states that sediments deposited in water form as horizontal layers

Original horizontality

The arrival times of which two types of seismic waves are used to calculate the location of an earthquake's epicenter

P and S

Earthquake early warning systems work on the principle that ____

P waves travel faster than S waves and surface waves but do little damage

The combined movements of the ____, ____, and ____ plates account for most of the seismic activity experiences in North America

Pacific, North American, and Farallon

Annualized earthquake losses are calculated from a number of factors, including ____

Population size, building types, shaking potential

Major movements occur at approximately the same time intervals describes ____

Quasi Periodic type of fault movements

Fault-movement timing groups fall into one of three classifications: ____ movements, ____ movements, and ____ movements

Quasi-periodic, clustered, and random

No definable pattern and inherently unpredictable describes ____

Random type of fault movements

The ____ rift is ancient, having formed about 550 million years ago

Reelfoot

Subduction-zone earthquakes are ____

Sometimes extremely powerful

Another term for an earthquake is a ____

Seism

The energy released when a fault ruptures radiates outward from the hypocenter as ____

Seismic waves

The study of earthquakes is known as ____

Seismology

Strike-slip faults form in response to which type of stress?

Shear

The enormous movements that occur along a fault when an earthquake occurs are referred to as ____

Slips

Which of the following accurately summarizes the earthquake hazard in Turkey?

Strong earthquakes and poorly constructed buildings built on top of soft sediments combine to make earthquakes in Turkey extremely hazardous

What is the cause of the powerful earthquakes and the resulting large tsunamis that occur in the area of Indonesia?

Subduction of an oceanic plate

Which type of tectonic setting has the largest number of strong earthquakes?

Subduction zones

Which type of tectonic setting listed below has the largest number of strong earthquakes?

Subduction zones

Why does short-term earthquake prediction currently appear impossible?

The detailed behavior of fault movements appears to be too unpredictable

Earthquakes in the region of Mexico City are caused by ____

The movements of the Cocos plate as it subducts along a downward thrust fault under the North America plate

The distance between two waves, labeled A in this figure, is called the ____. The height of a wave above its starting point, labeled B in this figure, is called the ____

Wavelength; amplitude