By Xinhua,
Los Angeles : An unusually intense swarm of earthquakes has struck beneath a small suburb of Reno in Nevada, leaving residents shaken and scientists puzzling over the cause, the Los Angeles Time said on Thursday.
Totaling more than 1,000 over the last two months, more than 20quakes of magnitude 2 or higher have hit on some days, and the intensity and frequency of the quakes have been increasing rather than following the normal pattern of tailing off, according to the paper.
Researchers say they have never seen anything quite like the “Mogul earthquake sequence,” as they have named it.
“We don’t know what is going to happen next,” said geologist James Dolan of University of Southern California, who has been watching the unfolding seismic activity. But a swarm like this “makes you perk up your ears and start considering the possibility that you might be in a heightened period of hazard.”
The swarm of quakes has unnerved the roughly 3,000 residents who live around Mogul, a sparse community of ranch homes about two miles (3.6 kilometers) west of Reno, the report said.
The Mogul sequence began Feb. 28 with a small tremor about a mile (1.6 kilometer) beneath the town. Over the following weeks, repeated small quakes struck the area.
About every third day or so, there would be a quake with a magnitude greater than 2 mixed in with the smaller temblors, said Nevada state geologist Jonathan Price.
The number of daily quakes grew slowly, and then a shift in the pattern occurred April 15, when magnitude 2 quakes began occurring about three times a day, according to the report.
On April 24, the area suffered a magnitude 4.2 quake, and the number of magnitude 2 quakes, which are slight but noticeable, jumped to 20 a day or more, Price said. Before April 22, there had been more than 400 quakes. Last week alone, there were 500, the report said.
The biggest series of quakes struck Friday evening — a magnitude 3.3 temblor, followed 11 seconds later by a magnitude 4.7, the strongest in the Reno area in more than half a century — and then a 3.4 three minutes after that, said the report.