Seismotectonics of the Wasatch Fault Zone

Haiyan Fu

Dina Freedman

8.30.11

The Wasatch Fault

• The Wasatch Fault is a normal active fault

• Transition between from the Basin and Range province to the Colorado Plateau

• Visible below the highest shoreline of Lake Bonneville

Figure 1: The Wasatch Fault visible near American Fork Canyon (UGS)

Earthquakes and Utah

• The Wasatch Fault is “Aseismic”• Probability of an earthquake M>7.5 is 25% during the

next century

Figure 2: The past 6000 years show 19 surface-faulting earthquakes (UGS, 1996)

Earthquakes

• Earthquakes in Utah are common

• Last major quake on the SL segment was 1200 YA

• On the Wasatch Fault, an earthquake in Herriman in 1992 was a magnitude 4.3

• The time between earthquakes or “clock” is unknown

Figure 3: Earthquakes in Utah (Chang and Smith, 2002)

Flooding Consequences

• Chang and Smith (1998) - flooding from the GSL would likely occur with a normal fault earthquake

• It could displace the lakeshore southward up to 3.5 miles

• Not only flood danger exists but soil liquefaction extending 100 miles from the center of a M 7.5 quake (USGS, 1996)

Figure 5: Effects of a 2 meter slip and a lake level rise to 4212’ in SLC on flooding. Adapted from Chang and Smith, 1998.