Southern Idaho Still Having Quakes, Scientists Don't Know Why

Months After a M6.5 Earthquake Struck Idaho, the Southern Part of the State Is Still Shaking and Scientists Don’t Know Why

By

 Strange Sounds

Months after a magnitude 6.5 earthquake struck Idaho, the southern part of the state is still shaking.

And scientists have no clues why…

But the region hasn’t stopped shaking since. The area has experienced a string of aftershocks in the months following the quake, some registering as high as magnitude 4.8.

The shaking has been so strong, in fact, that a popular beach along Stanley Lake in the Sawtooth National Recreation Area has sunk into the water.

“The most probable cause for the ‘disappearing’ of the inlet delta is a combination of liquefaction and compaction of saturated sediments and some possible sliding and later spreading on the delta toward the deeper part of the lake,” said Claudio Berti, director and state geologist of the Idaho Geological Survey.

Sawtooth Fault

The March 31 earthquake occurred 16 miles north of the Sawtooth Fault, a 40-mile stretch of fault line discovered nearly a decade ago. Geologists have largely believed the fault was inactive, but the latest round of quakes have reinvigorated interest in the region.

Geologists are puzzling over exactly what caused an earthquake in the otherwise quiet region. Some researchers suspect the Sawtooth Fault is actually longer than expected. Others believe the fault is now taking advantage of openings in Earth’s crust and is slowly pushing north. One theory suggests energy from the Sawtooth Fault could have jumped to a nearby unknown fault, spurring the recent series of earthquakes.

For now, the race is on to collect more data about the region, so that geologists can paint a clearer picture of what’s happening below surface. In addition to gathering seismic readings and analyzing soil samples, researchers will use LIDAR to hunt for signs of movement in the area.

In the aftermath of a major earthquake, it’s common for a series of smaller earthquakes, called aftershocks, to occur.

Aftershocks, which usually originate on the same fault line, can last for days, weeks, months and even years following the main shock. The larger the earthquake, the longer it’ll take the fault to get all that shaking out of its system.

In some cases, seismic energy along a fault line will build up over a long time. A 2009 paper in the journal Nature suggested earthquakes that occur far away from tectonic plate boundaries may be lingering aftershocks from temblors that happened centuries earlier. The pace at which two tectonic plates slide past each other could dictate how long aftershocks may last, with slower movement leading to longer last bursts of related seismic activity.