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Bluffdale Ground Keeps Moving; 139 Earthquakes So Far

BLUFFDALE, Utah — The series of small earthquakes in the south end of the Salt Lake Valley continued Monday with monitoring stations recording several more small tremors.

Since the seismic activity started on Feb. 13, there have been 139 earthquakes centered in the Bluffdale area, according to the University of Utah Seismograph Stations. The largest was a 3.7 magnitude on Feb. 15.

“I consider it a foreshock, mainshock, aftershock sequence,” said Jim Pechmann, a seismologist at the University of Utah.

The bulk of the temblors have been aftershocks, Pechmann said, with the largest aftershock hitting early Saturday morning and registering in at 3.1 magnitude—spawning a flurry of small quakes Sunday and Monday.

It’s not clear if the earthquakes are originating from the well-known Wasatch Fault or from a different, yet-to-be-named fault located below Bluffdale, Pechmann added.

The depth of the Bluffdale quakes makes it difficult to determine whether the Wasatch Fault is to blame, but history has shown that the 240 mile-long fault is not known for producing this type of small earthquake.

“Most of the time it likes to kick off magnitude 7 or so earthquakes rather than little earthquakes,” Pechmann said.

Jim Pechmann, Siesmologist at the University of Utah

The biggest misconception about the cluster of earthquakes, Pechmann said, is that it’s somehow delaying a larger, more catastrophic seismic event.

“Small earthquakes do not relieve enough pressure to delay a large earthquake,” he said. “They don’t act as a safety valve. In fact, they do increase the probability of larger earthquakes a little bit.”

The probability is roughly one in twenty that each quake could be a foreshock to a larger earthquake in five days, according to the U’s seismology department.

Since measurements started being recorded in 1962, the largest earthquake in the Bluffdale area was a 4.1 magnitude in March, 1992.

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