U of U Seismograph Stations Research: The Earthquake Clock Throughout the Wasatch Front Region

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Active Faults in the Wasatch Front Region Although the Wasatch Fault is a well known part of northern Utah, it is not as well known that this fault is only one of several known active faults of the Wasatch Front region. It is also not often realized that the known active faults are probably not the only faults with earthquake potential. There are several known "blind faults" that are not visible at the Earth's surface and an unknown number of additional "blind faults" that have not yet been detected because they have not had an earthquake within the last 30 years, the time since seismographs have been available in Utah. A map of the known active faults shows that there are potentially dangerous faults throughout the Wasatch Front area, such as in the West Valley City area, under the Great Salt Lake, and just north of the Great Salt Lake. Using mathematical probability calculations, the following table of average recurrence intervals has been established for the Wasatch Front Region. A recurrence interval is the time between earthquakes. These calculations are shown in the table below. The table reveals that the there is a relationship between earthquake size and recurrence interval. The smaller earthquakes occur more frequently. Recurrence Intervals for the Wasatch Front Region Magnitude Range Estimate of Recurrence Interval Time Since Last Earthquake Greater than 3.0 4 months 10 months Greater than 4.0 18 months 28 months Greater than 5.0 8.7 years 11.8 years Greater than 6.0 48 years 25 years Greater than 6.5 120 years 66 years Between 3.5 and 4.5 11 months 10 months Between 4.5 and 5.5 4.6 years 11.8 years Between 5.5 and 6.5 24 years 25 years An earthquake of magnitude 3.0 is generally only felt in the immediate area. An earthquake of magnitude 5.0 or greater is likely to cause damage. An earthquake of magnitude 5.5 is likely to cause significant damage and an earthquake of magnitude 6.0 will be a serious challenge to the Wasatch Front community. Modified from ????????? Using The Table As you can see, earthquakes with magnitudes between 4.5 and 5.5 are estimated to occur quite frequently in northern Utah (about once every 5 years). You can also see that it has been about 12 years since the last earthquake with a magnitude between 4.5 an 5.5 has occurred. Thus, the past pattern of earthquake activity would indicate that northern Utah should experience an earthquake within this magnitude range in the relatively near future. There is no method that allows a more accurate prediction as to exactly when or where, it can only be expressed as a likely probability for the northern Utah region. In a similar manner, earthquakes greater than magnitude 5.5 to 6.5 are estimated to occur about every 24 years somewhere in northern Utah. The last such earthquake was the magnitude 5.7 Cache Valley Earthquake in 1962. Consulting the data table indicates that past earthquake activity would indicate we are overdue for an earthquake between 5.5 and 6.5 in northern Utah. Again, this is a matter of probability and "likelihood", there is no accurate way to predict such an earthquake event in terms of exact time or location. Similar information is shown on the table for earthquakes of other magnitudes. The last column of the table, "Time Since Last Earthquake" is calculated from the current University of Utah Seismograph Stations earthquake data set and thus shows current information.