|
|||
  
 
 |
By Earl Scott
NORTH LOGAN -- Many people enjoy getting out in their back yards, digging in their gardens and playing in the dirt in general. Western Geologic has done all the back yard dirt diggers one better. It has dug a trench that runs east to west about 3 feet wide, 8 feet deep and 1,000 feet long into the side of the mountain above North Logan. "We have gotten several calls from residents in the area," said Winona Perry, North Logan City receptionist. "They want to know what is going on up there." What they are doing up there is a geological survey. Western Geologic has been contracted by a developer to see if the East Cache fault lies in the area as it is shown on the maps. "We are just beginning the preliminary work," said Bill Black. a geologist with Western Geologic. "It's way too early to tell if the East Cache fault is running along here." They did find evidence of old landslide activity in the area. "I can't tell how old the landslide deposit is yet," Black said. "It's really, really old though." The fault is split into three traces, or parts, and Western Geologic plans to dig one more trench to the south of the existing trench to cover the entire fault area. "We want to make sure we don't miss anything," Black said. "You don't want to build a house on top of a surface fault." The depth of a fault is an important factor in construction, Black said. The more shallow the fault, the less desirable the area is to build on. It takes about a 6.0 earthquake to break the ground, Black said. Earthquakes are measured on the Richter scale, with each whole number of magnitude equaling about 31 times more energy being released than the previous number. A 5.0 magnitude would be a heavy tremor, while a 6.0 would be considered a major quake. Normally ground fracturing occurs along a fault line and not at the epicenter of an earthquake, so knowing where a fault lies is important, Black said. Cache Valley is full of Lake Bonneville sediment that turns to jelly in an earthquake. "Liquefaction of the soil is bad in an earthquake," Black said. "When it gets shook, the soil loses its ability to support anything." There are many types of fault lines in seismically active areas, Black said. "The valley area has vertical slip faults; the ground moves up and down," he said. "Unlike most of California where the ground moves side-to-side." Western Geologic is not up in the hills above North Logan trying to predict an earthquake or the damage from one. "We're just conducting what's called a hazard engineering survey," Black said. "The developer just wants to know what's going on up here before any houses are built." Utah State University geology graduate students Scott Friedman, Alex Steely and Joe Jacobs have part-time jobs with the company during the project. "It's great field experience doing this," Friedman said. "I worked in Los Angeles for a year. I like this type of geology." Friedman's co-workers from USU echoed his sentiments and were happy to have the opportunity to work in the field. "We are just working as needed," Jacobs said. "We'll be out here for a few more days, but getting the experience is great." The biggest area of concern for an earthquake is from Brigham City to Salt Lake City, Black said. "Cache Valley has had some seismic activity in the past," he said. "The Wasatch Front is the big area of study for quakes right now. That area is probably due for a quake." According to the U.S. Geological Survey, there is a 30 percent chance of a major quake along the Wasatch Front in the next 100 years
NW |
||