Ch. 4 - HW (Plate Tectonics and Earthquakes)

If Alaska and California are ignored, the list of 10 largest U.S. earthquakes shows ____________.

10 events affecting at least 10 different states

California accounts for _______ of all U.S. earthquakes of magnitude 3.5 and above.

23%

Paleoseismologic analysis of trenches cut across faults and folds in the New Madrid, Missouri, area has led the U.S. Geological Survey to forecast a 25% chance of a magnitude __________ earthquake here within the next 50 years.

6 to 7

Several recent earthquakes in Washington's Puget Sound region were caused by movement of the subducting ______________ Plate.

Juan de Fuca

The __________ Rift is the rift below the New Madrid region and is responsible for the seismic activity in the area.

Reelfoot

Which state listed below is most likely to have a magnitude 9 or larger earthquake in the next several hundred years?

Washington

Prehistoric earthquakes may be interpreted using faulted pond sediments. The amount of offset of sediment layers from one earthquake is proportional to the ________________.

earthquake magnitude

When rock heats and liquefies into magma its volume _____________.

expands, and neighboring brittle rock must fracture and move out of the way

Earthquake epicenters east of the Rocky Mountains are in random locations and do not cluster in certain areas.

false

Earthquakes below Kilauea volcano are dominantly deep events in the mantle.

false

Eastern U.S. damages may be experienced over a smaller area than they would be for an equivalent-sized earthquake in California.

false

Historic earthquakes in the Rio Grande Rift area have had only small to moderate magnitudes, but the continental lithosphere continues to compress and shorten, thus presenting a real hazard for large earthquakes.

false

In the last 30 million years, the region between the eastern Sierra Nevada in California and the Wasatch Mountain front in central Utah has contracted in an east-west direction, so Nevada is now half of its former width.

false

Much of Utah's population lives within sight of the scarps of the 370-km-long Wasatch Front, the zone of reverse faults separating the mountains from the Great Basin.

false

On 28 October 1983, the Lost River Fault broke free for a magnitude 7.3 MS event, moving Borah Peak, Idaho's highest point, 4 m lower.

false

The Imperial Valley sits on an actively closing ocean floor.

false

The New Madrid and San Francisco earthquakes were of similar magnitudes, but the felt area of the New Madrid quakes was much smaller.

false

The bounding faults on the eastern side of the Great Basin are mostly down to the east, whereas the bounding faults on the western side (in eastern California and western Nevada) are down to the west.

false

The duration of shaking in 1985 in Mexico City was decreased due to seismic energy being trapped within the soft sediments.

false

The sizes of the felt areas of large earthquakes in North America are always the best indicator of earthquake magnitude.

false

The southernmost segment of the San Andreas Fault, from San Bernardino to the Salton Sea, is a complex zone that has generated several truly large earthquakes in historic times, but it has no locked zones within it.

false

Thrust faults that do not reach the surface are called dark thrusts.

faults

Which of the following states has the lowest earthquake risk?

florida

The Great Basin region between the eastern Sierra Nevada in California and the Wasatch Mountains in Utah ______________________ in response to plate-tectonic forces.

has expanded in an east-west direction

When compared to California, seismic energy in the eastern U.S. is transmitted __________.

more effectively in the older, more solid rocks

Another class of active faults is created by southern California pushing into the "Big Bend" of the San Andreas Fault; these faults are __________.

mostly east-west-oriented thrust faults (reverse faults)

Earthquakes in Hawaii are mostly related to ________________.

movement of volcanic magma beneath the ground

The dominant type of faulting in the Great Basin region is ______________.

normal faulting

Which of the following states has the highest earthquake risk?

Arkansas

We know that the part of California on the Pacific Plate will not break off in a giant earthquake and sink into the Pacific Ocean because ______________________.

of isostasy

The New Madrid earthquakes are apparently related to an old buried ____________.

rift zone

Which four states account for 91% of all U.S. earthquakes of magnitude 3.5 and above?

California, Alaska, Hawaii, and Nevada

When magma is on the move at shallow depths it commonly generates a swarm of __________.

small earthquakes referred to as harmonic tremors

The crustal thickness in the Great Basin is __________ than mid-continental North American crust.

thicker than oceanic crust and thinner

The large left step in the San Andreas Fault in the Los Angeles area causes compressive ruptures along east-west-oriented ________ faults as in the 1971 San Fernando and 1994 Northridge events.

thrust

Adjustments related to plate-tectonic activity cause earthquakes from Washington to New Mexico, from Montana to California, and at other points throughout the West.

true

Aftershocks of the 1811-12 New Madrid, Missouri, earthquakes are still occurring today.

true

As much as 20% of the relative motion between the Pacific and North American Plates may be accommodated by the extensional stretching of the Basin and Range province, leaving numerous north-south-oriented mountain ranges separated by down-dropped, sediment-filled basins.

true

Estimated Mercalli intensities of VIII (significant damage) from the new New Madrid quakes of 1811-1812 reached into Ohio.

true

Failed rifts remain as zones of weakness that may be reactivated by later plate-tectonic stresses to once again generate earthquakes.

true

Human activity has likely triggered earthquakes with magnitudes between 3 and 5.

true

In historic time, Nevada has averaged one earthquake with a magnitude in the 6s per decade and one with a magnitude in the 7s every 27 years.

true

In the Pacific Northwest, stresses are transmitted upward from the subducting plates, forming strike-slip faults that rupture the surface, as in Seattle.

true

In the central United States, ancient rift valleys remain from failed spreading centers and these ancient rifts today are zones of weakness whose faults can be reactivated due to long-distance effects of Atlantic Plate spreading and Pacific Plate collision.

true

In the last 6,000 years, a magnitude 6.5 or stronger earthquake has occurred about once every 350 years on one of the Wasatch System Faults, but no large earthquakes have been reported along the Wasatch Front Faults since the arrival of Brigham Young in 1847.

true

In the last three years alone (2014-2016), Oklahoma has accounted for roughly 10% of all earthquakes of states in the top 10 most active earthquakes states.

true

Most North American earthquakes occur in the west along the edges of the active plates, but the central and eastern regions also have earthquakes—not as many but just as large.

true

Nevada has several gaps in the belt of historic seismicity, suggesting residents in these seismic gaps may be in for some future earthquakes.

true

New England has a long record of significant earthquakes.

true

Ocean ridge spreading still occurs offshore of northernmost California, Oregon, Washington, and southern British Columbia, as well as in the Gulf of California.

true

Pumping fluids into Earth has been found to sometimes trigger small earthquakes (magnitudes < 5).

true

Rivers, such as the Mississippi River, have a drainage pattern that flows along a zone of weakness.

true

The 1994 Northridge event was similar to the 1971 San Fernando earthquake in magnitude, number of people killed, and type of faulting.

true

The New Madrid, Missouri, 1811-1812 earthquakes have never been equaled in the history of the United States for the number of closely-spaced, large seisms and for the size of the felt area.

true

The New Madrid, Missouri, 1811-1812 earthquakes were felt from Canada to the Gulf of Mexico and from the Rocky Mountains to the Atlantic seaboard, where clocks stopped, bells rang, and plaster cracked.

true

The Owens Valley quake of 1872 is estimated to have had a magnitude of 7.8 to 8, indicating that big earthquakes can and do happen far away from the coastal zone and the San Andreas Fault.

true

The Rio Grande Rift in New Mexico, Colorado, westernmost Texas, and Mexico is one of the major continental rifts in the world where the continental crust is being heated and stretched from below.

true

The epicenters of the larger New Madrid, Missouri, earthquakes line up along the Mississippi River Valley, possibly because of an ancient rift valley, known as the Reelfoot Rift, formed about 550 million years ago.

true

The subducting Juan de Fuca Plate is only 10- to 15-million-years old and is warm and buoyant. However, as it is subducted, its density increases, causing a buildup of stress.

true

The zone of dangerous faults in Southern California is much wider than in the San Francisco Bay area, largely because the major plate-bounding fault (the San Andreas) is bent so far to the west that it makes it difficult for the Pacific Plate to slide along on its northwestward journey.

true

Which of the following factors is the reason for the increase in Oklahoma earthquakes over the past 3 years?

wastewater disposal

Today, North America has several small- to medium-sized plates subducting beneath its ____________.

western margin

When the part of California west of the San Andreas Fault plows into Alaska it will __________.

become part of Alaska's southern margin

The 17 January 1994 Northridge earthquake in Los Angeles was generated on a _______ thrust fault.

blind

Organic material in sediment layers is dated by measuring the amount of radioactive ________ present.

carbon

Which of the following represents evidence for major fault movement on the Seattle Fault zone about 1,100 years ago?

All of these choices are correct.

In the last 5.5 million years, rifting action tore Baja California and California west of the San Andreas Fault from the ______________.

North American Plate and piggybacked them onto the Pacific Plate

At Hebgen Lake in 1959 an earthquake larger than magnitude 7 greatly affected ____________.

Yellowstone National Park

On 3 November 2002, a large earthquake occurred in __________. Because of its similarity to the 1857 Fort Tejon earthquake on the San Andreas Fault, this event has been compared to the much-anticipated "Big One" in Southern California.

alaska

Which state accounts for the greatest percentage of all U.S. earthquakes of magnitude 3.5 and above?

alaska

The Charleston, South Carolina, earthquake of 1886 occurred along a seismic belt that may be related to _________________.

an adjacent oceanic fracture zone on the Atlantic seafloor