Exam 5: Earthquakes Throughout the United States and Canada

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

The San Andreas fault's earthquakes in historic time include which of the following?

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

Human activity has induced powerful earthquakes (magnitudes > 6).

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

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

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

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 ______________________.

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

How does a locked zone of a large strike-slip fault catch up with a creep zone?

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.

When rock heats and liquefies into a magma its volume _____________.

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.

The ________ segment of the San Andreas fault is the only one not to have a long rupture in historic time.In prehistory,it has ruptured every 250 years on average,but the last big movement was in 1680.

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

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.

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

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

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.

Which of the following states has the highest earthquake risk?