【on.cc東網專訊】 美國加州小城聖拉蒙（San Ramon），在過去一周內發生250多次地震，震級均在黎克特制3.6級以下。惟地震專家指，發生大地震的可能性很低，民眾不必驚慌。
聖拉蒙位於三藩市以東約57公里，人口約7.3萬。由10月13日起，小城已連續發生了250多次地震，震級從0.8級至3.6級，震感最強時波及鄰近城市。雖然居民對大多數地震毫無知覺，財物亦無遭到大損壞，但如此密集的地震還是令人不安。
有民眾擔心，不斷的小地震會導致大地震到來。地震學家敏森對此並不認同。敏森指，聖拉蒙所處的斷層，正在不斷透過小地震釋放壓力。雖然這樣密集地震的確不尋常，但該地區發生6.7級以上地震的可能性很低，未來30年只有7%。 美國地質勘探局曾預測，三藩市灣區未來20年發生6.7級以上地震的機會是72%。
www.zerohedge.com
As CBS LA reports, JPL experts predict a possible 5.0 magnitude quake in Los Angeles, but say it very well could be stronger.
JPL geophysicist Dr. Andrea Donnellan, along with seven other scientists, has been using radar and GPS to measure Southern California’s chances for a sizable earthquake, and has made a sobering hypothesis about another big one.
“When the La Habra earthquake happened, it was relieving some of that stress, and it actually shook some of the upper sediments in the LA basin and moved those a little bit more,” Dr. Donellan said.
However, according to Dr. Donnellan, those strains remain, with enough power to produce an even larger quake in the same epicenter in La Habra.
“There’s enough energy stored to produce about a magnitude 6.1 to 6.3 earthquake,” Dr. Donnellan described.
The new NASA-led analysis of a moderate magnitude 5.1 earthquake that shook Greater Los Angeles in 2014 finds that the earthquake deformed Earth's crust across a broad region encompassing the northern Los Angeles Basin and northern Orange County. As Fox LA adds rather ominously,
The shallow ground movements observed from this earthquake likely reflect strain accumulated on deeper faults, which remain locked and may be capable of producing future earthquakes.* * *
"The earthquake faults in this region are part of a system of faults," said Donnellan. "They can move together in an earthquake and produce measurable surface deformation, even during moderate magnitude earthquakes. This fault system accommodates the ongoing shortening of Earth's crust in the northern Los Angeles region.
Tectonic motion across the Los Angeles region is distributed on an intricate network of horizontally and vertically moving faults that eventually release accumulated strain in the form of earthquakes, such as the destructive 1994 magnitude-6.7 Northridge earthquake.
Donnellan said a future earthquake to release the accumulated strain on these faults could occur on any one or several of these fault structures, which may not have been mapped at the surface. "Identifying specific fault structures most likely to be responsible for future earthquakes for this system of many active faults is often very difficult," she said.
Seismologists at the US Geological Survey have questioned that probability, suggesting it may in fact be slightly lower, stating: “…the accepted random chance of a (magnitude five) or greater in this area in three years is 85 percent, independent of the analysis in this paper.”
USGS uses different methods from radar and GPS, such as fault maps and models, to develop their results.
Regardless of the discrepancy in percentage, scientists agree that the probability of at least a moderate-sized earthquake in Los Angeles over the next three years is high.
“We all need to be prepared. That’s not new for LA.”
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