Exam 5: Earthquakes Throughout the United States and Canada

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

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 near settlements including Albuquerque,Socorro,and Las Cruces in New Mexico,El Paso in Texas,and Ciudad Juarez in Mexico.

The creeping movements along some segments of the San Andreas fault are shown by millimeters per year of offset of sidewalks,fences,buildings,and other features.

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.

The spreading-center segment at the southern end of California's Salton Sea is marked by all but which of the following?

The New Madrid earthquakes are apparently related to ______________.

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.

The duration of strong ground shaking in the 1964 Alaskan Good Friday earthquake was 3 to 4 minutes.

The 1985 Mexico City earthquake was caused by eastward subduction of a small plate,the Cocos plate,beneath the North American plate.Other small plates are subducting beneath North America at the Cascadia subduction zone.

Recent work has shown that the last major earthquake in the Cascadia subduction zone occurred about 9 p.m.on 26 January 1700 and was about magnitude 9.This is known by __________________.

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

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

When the part of California west of the San Andreas fault plows into Alaska it _______________.

Another class of active faults is created by southern California pushing into the "Big Bend" of the San Andreas fault.These faults are __________________.

The biggest earthquake ever recorded instrumentally occurred on 22 May 1960 in southern Chile with a seismic moment magnitude of 9.5.

Because many of the thrust faults in the Los Angeles area do not reach the ground surface,their sound waves do not reach the surface with audible strength,so they are called deaf thrusts.

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

Constraining bends in large strike-slip faults commonly "lock up";thus,movements there tend to be _________________.

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.

Major southern California faults,such as the Imperial,San Jacinto system,Cerro Prieto,Elsinore,and Laguna Salada,also appear to be part of the San Andreas plate boundary fault system carrying peninsular California to the northwest.