Measuring Waves in Utah

In collaboration with researchers at the Utah Geological Survey, University of Utah, Utah State University, Brigham Young University, San Diego State University, and private industry, the Geologic Hazards Team Intermountain West MegaProject has conducted several high-resolution seismic imaging investigations along the Wasatch front, in order to better characterize earthquake hazards and ground motion in this region. These studies, to date, have been focused in the Salt Lake and Utah Valleys.

To conduct their study, scientists used shaker trucks to model what happens during an earthquake. Two different types of shaker trucks have been used in the studies. The small ones, called “minivibes”, gently shake the ground and provide information about the ground structure down to about 100 feet (approximately 30m) below the surface. The larger-scale shaker trucks, called “Liquidators”, generate long-period (low-frequency) seismic waves that penetrate deeper into the crustal structure down to 1000 feet (approximately 305m). The shaker trucks can shake the ground either in the horizontal direction to generate P-waves, or in the vertical direction to generate S-waves.

From the echoes that are recorded as the seismic waves bounce back to the surface from the various geologic structures beneath, we can create a subsurface image and estimate how fast seismic waves travel beneath a site. Both the image and the wave speeds are important to more accurately determine how the soils and rock will behave during an earthquake.


Source: http://earthquake.usgs.gov/regional/imw/imw_seis/ (public domain)