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)travel 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 earthquake 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 per-cent of the citys buildings are old and weak.Analyses suggest that another massive earthquake would cause extensive damage.
People who live there tend to feel safe because San Francisco has remained pretty quiet for a while.According to the new reseaych,however,its not a matter ofif the Big One will hit.Its just a matter of when.
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