ST. GEORGE — An earthquake struck northeast of Pine Valley early Tuesday morning, the first in a series of three quakes to hit the region.
The quake was reported shortly after 3:30 a.m. approximately 14 miles east of Enterprise, measuring magnitude 3.8 by the University of Utah’s Seismograph Station. It was followed 10 minutes later by a second quake measuring magnitude 2.1 and a third measuring 2.7 three hours later.
Emergency dispatch in St. George reported they have not received any calls from residents either reporting or inquiring about the quake. Cedar City emergency dispatch also said they were aware of the quake but have not received any calls from residents reporting it.
Iron County Sheriff’s Lt. Del Schlosser said there were reports that residents in New Harmony and Enterprise felt the quake but that he was not aware of any reports that were called in.
The Seismograph Station had received four reports from people who said they felt the quake, which was strong enough to have created light shaking at its epicenter. Steven Bowman, hazards program manager with the U.S. Geological Survey, told St. George News the epicenter was located in a valley or basin, where the energy waves tend to bounce back and forth and increases the shaking.
Referring to a 3.8 earthquake occurring in that area, Bowman said, “You should feel that.”
Bowman went on to say that the geological make-up of where the earthquake occurs plays an important role in the force or shaking it can produce. If the epicenter is near rock, the force or shaking is dampened as it travels through the hard material. Clay or soil, he said, will amplify the shaking, as there is less resistance as it moves through the soft material.
With Tuesday’s quake having occurred in a valley, he said it caused the shaking to reverberate much like water in a bowl, which can amplify the shaking further.
There are more than 900,000 earthquakes annually worldwide measuring 2.5 or less – which are typically not felt but will register on seismological equipment – and about 30,000 that are between 2.5-5.4 and that are often felt but only cause minor damage, similar to the earthquake reported Tuesday morning.
While Utah is not located on a boundary between tectonic plates, which is where most of the world’s earthquakes occur, it is sitting on the western part of the North American plate, so any interactions with the Pacific plate can cause an earthquake along any one of the faults across Utah.
Bowman said the Wasatch fault is the largest fault in the state, which is capable of producing up to a 7.0 earthquake. He also said that depth is important, since most quakes occur at shallow depths, which generally tend to be more damaging than deeper quakes because the shaking is more intense due to it being closer to the Earth’s surface.
Conversely, seismic waves from deep quakes have to travel farther to the surface, losing energy along the way. While they may be less damaging, they are typically more widely felt, and it also takes depth to create the larger quakes.
The maximum depth of any reported earthquake is roughly 430 miles below the Earth’s surface.
According to The Associated Press, a total of six earthquakes of magnitude 3.0 or greater have happened in the same area as Tuesday’s quake since since 1962, the largest of which was a magnitude 4.2 temblor in 1981.
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