All shook up: Concerns and explanations on the recent quakes

Between Feb. 11 and Feb. 13, the citizens of Lehi claimed to have felt the Earth move under their feet, and unlike those of us who have sung karaoke to Carole King before, they were being completely serious.  On Friday and Sunday, the city of Lehi and surrounding rural areas reported feeling a total of three quakes. According to the University of Utah Seismograph Station, the first quake struck roughly around 7:38 p.m. on Friday night with a reported magnitude of approximately 2.5. The second, a 2.6, jolted residents awake around 2:25 a.m. on Sunday morning, and the third, a 2.8 and the biggest of the three, rattled residents one final time, concluding the triplet at 6:09 p.m. So while the rest of Utah County were gathering up roses and boxes of Russell Stovers in preparation for Valentine’s Day, some of the constituents of Lehi were gathering up food storage and 72-hour kits in alertness of a possible impending natural disaster.

Although some of us may be privy to the exact causes and explanations of a quake, many people may dismiss it as some unknown phenomenon related to volcanoes, some kind of movement to do with underground plates, or one of the innumerable apocalyptic theories that have been circulating around in the mainstream lately. According to geologists, there are two main types of earthquakes: tectonic earthquakes and volcanic earthquakes. Tectonic earthquakes are caused by tectonic activity, which triggers when the Earth’s crust, comprised of many floating plates, becomes subjected to and moves freely because of strain. During these strain-induced movements, the plates can come towards each other, move away from each other or try to slide past one another. The first and third are the main causes of the earthquakes that we feel, being most commonly near the plate’s margins or a fault – a break in continuity along planes of rock.  The causes of the Lehi quakes are related to faults, and according to Mark Milligan of the Utah Geographic Survey, we’re host to quite a few of them, and possibly a single massive one.

“All of the faults within Utah County are related to the great Wasatch Fault that runs parallel to the Wasatch Mountains all throughout Utah.” says Milligan. “The quakes that have taken place in Lehi were due to one of the numerous smaller faults, most possibly due to ones that are under Utah Lake, as there are quite a few of them there.”

While we commonly feel tectonic earthquakes the most often, volcanic earthquakes are the sort which get the most spotlight and coverage in Hollywood films. Volcanic earthquakes are seismic motions that are caused by the sporadic movement of magma usually underneath the Earth’s crust and within the mantle, inducing pressure changes in the areas of rock in which the magma goes under stress. They usually occur above or around “hot spots” – specific regions within the mantle where the temperature is comparatively higher than the areas surrounding it. Although Utah has no “hot spots,” there is a significant one pretty near by – the Yellowstone Park Caldera.

“Hot spots are basically long volcanisms within the mantle and oceanic lithosphere,” says Henry Heasler, PhD volcanic geologist and coordinating scientist for Yellowstone National Park. “It’s a very complex process to what exactly happens underground, but basically the plates are moving above very centered and focused heat sources, where rocks are melted and magma is generated. In turn, these [plates] push against the subsurface continental layers and produce clusters of earthquakes otherwise known as ‘earthquake swarms.’”

Many citizens, like those in Lehi who were caught in a brief physical example of all of this geological jargon, have reported that they’re afraid that the two types of quakes may be interconnected – specifically, it may be a warning sign of a fabled, gargantuan 8.0 quake. Moreover, they fear that the recent quakes may be connected to a possible volcanic eruption. Are these legitimate concerns and worries, and should we start preparing for a cataclysmic disaster? Before you start crying “2012!” or consulting a van-dwelling Woody Harrelson on the hillside, you should know that while experts don’t dismiss it entirely, they do say the majority of the alarmism is just irrational speculation.

“The Wasatch Fault is in no way connected to Yellowstone whatsoever. The quakes that the people of Lehi felt are produced from localized faults and happen very often; we just don’t feel them the majority of the time,” says Milligan. “As far as the frequency of occurrence, [earthquakes] happen randomly; they haven’t been increasing or decreasing. They have no trend.”

As for the big expected eruption of the Yellowstone Caldera, Heasler reassures us that we shouldn’t be expecting it at all. “There are no concrete predictors or change of behavior recently as far as the caldera is concerned,” replies Heasler. “So there’s no need for alarm. At the same time we shouldn’t rule an eruption out. What we study is what happens down a hundred miles beneath the Earth’s surface. The farther away something is, the harder it is to sense it or see it. We’re pushing very advanced technologies to the limits, and as those instruments improve, the view improves and then there’s no doubt there’ll be modifications to theories or hypotheses – science is always a progress report.”

We now know that the small quakes are very common, that we are in no way connected to Yellowstone and that Yellowstone itself is the same as it always has been. But what about the “big one” that people have been claiming should happen any day now, which some have theorized could be at an 8.0 level?

“For the SLC segment,” replies Milligan, “there’s been a major earthquake every 1200 to 1300 years. On a geologic time scale, the next big earthquake could be as soon as a hundred years, maybe a little more. For the Provo segment, there’s a much longer interval, and they occur less frequently. Plus, the last one occurred less than a thousand years ago, so Utah County shouldn’t be expecting any major events within the near future.  In the meanwhile, the usual small quakes will continue occurring as they always have.“

After all of this, it looks like we won’t be seeing the Hollywood-sized natural catastrophe that we were all expecting. However, experts say that they are not impossible; they just have a very miniscule chance of happening anytime soon. We don’t have to return our 72-hour kits, nor keep them bedside. We can go back to worrying about the day-to-day and occasionally entertain our favorite imaginary (and in this case more plausible) zombie apocalypse scenarios. Business as usual.

One Response to "All shook up: Concerns and explanations on the recent quakes"

  1. Riaz Hussain Rajper   March 3, 2011 at 7:08 am

    This earthquake swarm may be triggered by human activities which induced in-equilibrium in local subsurface geology of the area. it may be due to withdrawal of huge quantity of groundwater through pumping for irrigation/domestic purpose, which caused rapid drop in the water table. Massive limestone beds at depth are also causing development subsurface caves through infiltration and percolation of acidic rain water/waste water, rapid movement of air trapped in subsurface caves may also trigger local seismic tremors during the flood seasons. Injection of untreated industrial/municipal waste-water may also accelerate the soil creeping movement or block movement along local normal fault plane. Keeping in view the above factors studies may be carried out regarding the evaluation of induced seismicity to diagnose the factors behind these local tremors and remedy steps may be taken to avoid…

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