U of U Seismograph Stations Research: Basic Information about Active Faults of Utah

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Active Faults in Utah The surface of the Earth in the region of the Great Basin has been profoundly affected by, and in fact created by, faults similar to the Wasatch Fault. It is interesting to compare the Earth's surface in the region known as the Great Basin with other areas of the western U.S. on a digital relief map*. Take a moment to examine this map and note the differences in the surface of the Earth in the region of western Utah and Nevada. Most of Utah's population lives on the edge of this geographic region called the Great Basin or "Basin and Range country". There is a direct link between the earthquake activity of Utah and the landforms that occur in the Great Basin. If you haven't already done so, note the definite north-south trends to the mountains and valleys of the Great Basin. There is a reason for this pattern in these landforms. * This map is provided at the website of Andrew Birrell and subject to his copyright. See more information about this and other relief maps of the United States. The Earth's crust throughout the Great Basin is being extended in an East-West direction. The Basin and Range topography (mountain-valley-mountain-valley) that we know today was created by earthquakes. As a result of the tension in the crust, the block of rock above the fault drops down relative to the block of rock below the fault. As the repetition of earthquakes over long time periods cause the blocks of rock to slide by each other along the fault within the Earth's crust, the surface of the Earth is affected. Repeated earthquakes move one block of rock continously upward, at the same time the block of rock on the opposite side of the fault continously moves downward. Below is a diagram representing a simple model of how blocks of rock move on normal faults.     The surface of the Earth is changed over geologic time as the block of rock which rises creates a mountain range, and the block of rock which drops creates a valley. The Wasatch Fault, along with the associated Wasatch Mountains and Salt Lake Valley, are an example of one specific fault which is active in this process forming the Great Basin, where extension in the Earth's crust is resulting in associated mountain building on the Earth's surface. The Wasatch Fault is very similar to most other active faults in Utah and can be used as a representative model for most active faulting in Utah. This fault intersects the surface of the Earth at the base of the Wasatch Mountain range. As the fault is followed down into the Earth's crust, it begins to curve into less steep angles and then flattens out as it extends west, under the Salt Lake Valley. Thus the Wasatch Fault is not a vertical fault; instead, it dips westward and the surface along which earthquakes can occur lies everywhere under the valleys west of this fault. For a diagram showing what scientists think the Wasatch Fault looks like at depth, click here http://www.ugs.state.ut.us/fmodel.gif The north-south trending mountains and valleys of the Great Basin all have their origin related to north-south trending faults which run parallel to the base the each range. Although the Wasatch Fault is a well known part of northern Utah, there are many other known active faults of the Wastach Front region and throughout the Great Basin. Almost all active faults in Utah have the same type of geometry as the Wasatch Fault and they all underlie the valleys located to the west of the faults to some degree that varies with the size of the specific fault. The exact size of all faults in Utah, including the Wasatch Fault, are not well known and are one of the lines of research that the University of Utah Seismograph Stations continuously works on. To see fault maps for Davis, Salt Lake,Utah, and Weber counties, click here.