Two buildings on the San Jose ca

共用题干
A Great Quake Coming?

Everyone who lives in San Francisco knows that earthquakes are common in the Bay Area一and they
can be devastating. In 1906,for example,a major quake destroyed about 28,000 buildings and killed
hundreds,perhaps thousands of people.Residents now wonder when the next"Big One"will strike.It's
bound to happen someday. At least seven active fault（断层）lines run through the San Francisco area. Faults
are places where pieces of Earth ' s crust（地壳）slide past each other. When these pieces slip , the ground
shakes.
To prepare for that day,scientists are using new techniques to reanalyze the 1906 earthquake and pre-
dict how bad the damage might be when the next one happens.
One new finding about the 1906 earthquake is that the San Andreas fault split apart faster than scientists
had assumed at the time. During small earthquakes,faults rupture（断裂）at about 2.7 kilometers per second.
During bigger quakes,however,ruptures can happen at rates faster than 3.5 kilometers per second.
At such high speeds,massive amounts of pressure build up,generating underground waves that can
cause more damage than the quake itself. Lucky for San Francisco , these pressure pulses（脉冲）traveled
away from the city during the 1906 event.As bad as the damage was,it could have been far worse.
Looking ahead,scientists are trying to predict when the next major quake will occur. Records show that
earthquakes were common before 1906.Since then,the area has been relatively quiet.Patterns in the data,
however,suggest that the probability of a major earthquake striking the Bay Area before 2032 is at least 62
percent.
New buildings in San Francisco are quite safe in case of future quakes.Still,more than 84 percent of the
city's buildings are old and weak.Analyses suggest that another massive earthquake would cause extensive
damage.
People who live there today tend to feel safe because San Francisco has remained pretty quiet for a
while.According to the new research,however,it's not a matter of"if" the Big One will hit.It's just a mat-
ter of when.

Earthquakes rarely happened in San Francisco before 1906.
A:Right
B:Wrong
C:Not mentioned