Earthquakes U.S and Canada Exam Chapter 5 Solved 100%

In the last 5.5 million years, rifting action tore Baja California and California west of the San Andreas Fault from the_______ - ANSWER-North American Plate and piggybacked them onto the Pacific Plate 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 ______________________. - ANSWER-Of Isostasy When the part of California west of the San Andreas Fault plows into Alaska is will________ - ANSWER-Become part of Alaska's southern margin Today, North America has several small- to medium- sized plates subducting beneath its_______ - ANSWER-Western margin 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 - ANSWER-Thrust Another class of active faults is created by southern California pushing into the "Big Bend" of the San Andreas Fault; these faults are __________. - ANSWER-mostly east-west-oriented thrust faults (reverse faults) Prehistoric earthquakes may be interpreted using faulted pond sediments. The amount of offset of sediment layers from one earthquake is proportional to the ________________. - ANSWER-earthquake magnitude Organic material in sediment layers is dated by measuring the amount of radioactive ________ present. - ANSWER-carbon 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. - ANSWER-Alaska The 17 January 1994 Northridge earthquake in Los Angeles was generated on a _______ thrust fault. - ANSWER-blind If Alaska and California are ignored, the list of 10 largest U.S. earthquakes shows ____________. - ANSWER-10 events affecting at least 10 different states Which state accounts for the greatest percentage of all U.S. earthquakes of magnitude 3.5 and above? - ANSWER-Alaska California accounts for _______ of all U.S. earthquakes of magnitude 3.5 and above. - ANSWER-23% Which four states account for 91% of all U.S. earthquakes of magnitude 3.5 and above? - ANSWER-California, Alaska, Hawaii, and Nevada Which of the following states has the lowest earthquake risk? - ANSWER-Florida Which of the following states has the highest earthquake risk? - ANSWER-Arkansas Which state listed below is most likely to have a magnitude 9 or larger earthquake in the next several hundred years? - ANSWER-Washington Several recent earthquakes in Washington's Puget Sound region were caused by movement of the subducting ______________ Plate. - ANSWER-Juan de Fuca Which of the following represents evidence for major fault movement on the Seattle Fault zone about 1,100 years ago? - ANSWER-All of these choices are correct. The Great Basin region between the eastern Sierra Nevada in California and the Wasatch Mountains in Utah ______________________ in response to plate-tectonic forces. - ANSWER-has expanded in an east-west direction The dominant type of faulting in the Great Basin region is ______________. - ANSWER-normal faulting The crustal thickness in the Great Basin is __________ than mid-continental North American crust. - ANSWER-thicker than oceanic crust and thinner At Hebgen Lake in 1959 an earthquake larger than magnitude 7 greatly affected ____________. - ANSWER-Yellowstone National Park The New Madrid earthquakes are apparently related to an old buried ____________. - ANSWER-rift zone When compared to California, seismic energy in the eastern U.S. is transmitted __________. - ANSWER-more effectively in the older, more solid rocks 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. - ANSWER-6 to 7