Wong, I. Utah Geological Survey. Skip to content. A fault runs through it The Wasatch Fault Zone runs about miles kilometers from Central Utah to Northern Idaho and has been divided into 10 individual fault segments. Wasatch Fault ground shaking attenuates faster than predicted Moschetti and his team compiled a database of ground motion recordings from 59 earthquakes since — nearly half of which came from the Magna earthquake sequence — and identified regional features affecting earthquake hazards.
Author Recent Posts. Latest posts by Temblor see all. A trench usually takes one day to excavate, although this time can vary depending on the size of the trench or if more than one trench is excavated. Corner Canyon site trench excavation. As soon as the excavator does its job, the paleoseismologists get to work cleaning the walls of the trench, much like archeologists cleaning an archaeological site. They want to make the trench walls as "clean" as possible and to prepare a fresh geologic exposure of the sediment layers and the faults that cut and offset these layers.
Preserved in the trench walls is the geologic and tectonic record of paleo-earthquakes at this location along the Wasatch fault zone. The trench is ready now for the scientists to set up a coordinate system on the vertical walls of the trench so that all the information can be precisely recorded. String and nails are used to create a grid on the trench walls. These horizontal and vertical grid lines are spaced exactly 1 meter apart, like a graph-paper overlay.
Next, detailed photos are taken of the entire extent of the trench walls and are pieced together to create a photo mosaic of the trench. In the past this task was done manually and took several dozen person-hours. Recently, new software automatically creates a photo mosaic with more accuracy and requires fewer person hours. The software also creates a 3-dimensional model of the trench that can be rotated and manipulated to reproduce a virtual trench that can be studied long after the real trench has been filled in.
Once the trench grid is set and the trench photo mosaics are printed, paleoseismologists can begin logging the trench. Paleoseismologists examining the trench walls at the Alpine site. View of Flat Canyon site after trench is backfilled with dirt. Thumbnail for the model that was created by Nadine Reitman, U. Geological Survey. Download and interact with 3-D model of the Alpine trench. Model created by Nadine Reitman. A time-lapse video of the excavation of the trench for a paleoseismology research project at Flat Canyon, Utah, along the Wasatch fault zone.
Collecting data at the Flat Canyon site. The trench log is a map of the trench wall drawn on a small-scale paper print out of the trench photo mosaic. Paleoseismologists record details of the trench walls onto the trench logs. These details include the location and type of geologic contacts between layers of sediment a. Careful descriptions of color, grain size, moisture, and density are recorded for each geologic unit. Samples of important geologic units are collected and sent to a laboratory to be age-dated.
The geologic age of a sample is determined by various age-dating techniques, such as carbon dating and luminescence dating. The deformation of sediment, faults, and other features in the trench walls tell the sequential story of past earthquakes at that location, and age-dating informs paleoseismologists when the past earthquakes happened. Collecting all the data to reconstruct the story takes a team of scientists about two weeks in the trench, carefully recording everything onto the trench log.
When the job is done they celebrate with a "trench party", where interested scientists and local citizens are invited to tour the trench and discuss the geologic interpretations before it is filled in. To the west, in urban Salt Lake City , a 4-mile-wide 6 km zone of fault segments called the West Valley Fault Zone stretches north-northwest for 9 miles 14 km beneath the valley. Trenches along a portion of the West Valley fault zone, near Salt Lake City's airport, reveal that both the West Valley and Wasatch faults seem to rupture simultaneously during earthquakes, scientists will report today at the meeting.
While dating techniques can't confirm that the earthquakes were synchronous, instead of within a few days, month or years, modeling suggests they strike at the same time, said Christopher DuRoss, study co-author and a geologist at the Utah Geological Survey. If both fault zones ruptured during an earthquake, it would mean more shaking for Salt Lake City, which sits atop soft lake sediments, the kind that experience liquefaction during severe earthquakes.
In the Christchurch, New Zealand earthquake, liquefaction destroyed the city's downtown core. In Salt Lake City, planners are also concerned about the risk of flooding from waves in the Great Salt Lake and landslides in mountain canyons during a major earthquake.
Geological Survey release updated hazard maps in , which are based on today's presentation and other recent work, DuRoss said. You must be logged in to post a comment. The largest and highest risk fault is the Wasatch fault, which extends from southernmost Idaho, through the Wasatch Front, to south of Nephi.
The Wasatch fault, especially the central part, has been the subject of dozens of detailed scientific studies that demonstrate its high risk. Studies indicate that Utah is due or overdue for a devastating earthquake Utah Geological Survey. These studies show that the central most active part of the Wasatch fault has averaged one very large magnitude 6. The last major earthquake on the central Wasatch fault was on the Nephi segment about years ago.
However, the actual spacing between past major earthquakes on the central Wasatch fault varied greatly from a few years to over years, decreasing our ability to predict earthquakes. Most people have heard of the Wasatch fault, but few are aware that Utah has up to other large faults that could also produce devastating earthquakes; most in the western half of the state.
Very few studies have been done on these other faults, such that we know very little about how often they rupture or how big the earthquake is likely to be.
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