Research Abstracts Online
January 2009 - March 2010
University of Minnesota Duluth
Swenson College of Science and Engineering
Large Lakes Observatory
PI: David Dolenc
Effects of Shallow Three-dimensional Structure of the Mississippi Embayment on Ground-motion Amplification
The Mississippi embayment region contains the New Madrid Seismic Zone (NMSZ), the most seismically active region in the central and eastern United States. This region is capable of producing M8 earthquakes. At the same time, the embayment region is covered with up to 1 km thick low-velocity unconsolidated sediments that are known to amplify ground motions. Because large earthquakes in the NMSZ are infrequent, the effects of the shallow structure on the wave propagation in the Mississippi embayment remain to be better quantified. This researcher uses finite-difference code WPP with one-dimensional and three-dimensional velocity and attenuation models of the Mississippi embayment to simulate five M4.0-5.2 earthquakes that were well recorded on the regional broadband seismic network. The results are compared to evaluate the effects of the shallow structure on the ground-motion amplification, trapping of the surface waves in the slow velocity structures, and focusing and interference effects at the basin edge. The synthetic waveforms are also compared to the observations to evaluate the three-dimensional velocity model. This study will provide a better understanding of why and where the strong ground motions as well as extended duration of shaking can be expected in the Mississippi embayment due to slow velocity structures. The study will further provide an estimate on the importance of including slow velocity layer as well as three-dimensional structure and attenuation in the numerical simulations within the Mississippi embayment. In addition, the comparison of the synthetics to the observations will be used to evaluate the regional three-dimensional velocity model.