Gregory D. Bensen
Graduate Research Assistant
Center for Imaging the Earth's Interior
Department of Physics
Campus Box 390
University of Colorado at Boulder
Boulder, Colorado 80309-0390
Tel: 303-819-0523
gbensen@colorado.edu
Current Research
Technical aspects
My research focuses on surface wave tomography studies of North America. Primarily, I've been working with my colleagues to develop the procedure of creating surface wave Green functions through cross-correlation of long noise timeseries. These cross-correlations of long noise time-series, or Empirical Green Functions (EGFs), are like recorded Rayleigh and Love wave earthquake surface wave signals but with certain specific differences. Advantages include
- accurate measurements to short periods, providing information about shallower structures
- shorter average path length, constraining velocity on a smaller region
- high path density over potentially large regions
- reliable signals in regions generally devoid of earthquakes
- precise knowledge of source and receiver location
- precise knowledge of initial phase
- new utilization of existing data
Some downsides also exist relative to earthquake signals. Long period measurements are more difficult due to poor signal quality. We generally can compute good cross-correlations between 6 and 75 seconds period for Rayleigh waves and 6 and 25 seconds period for Love waves.
Science questions to address
Below is a map of the study area for my research with permanent and temporary stations used marked with black triangles. Two years of data from about 200 stations were used to compute nearly 20,000 EGFs. Lower station density in the central and eastern US limit the resolution achieved in those regions. New stations installed as part of the USArray experiment are being used by my collaborator, Morgan Moschetti, for a similar study.
Working towards the goal of a 3D shear wave velocity model of North America, it is important to think of what lingering scientific questions can be addressed with our results. In our 2D dispersion maps, we observed an improvement in resolution of 5 to 10 times compared to teleseismic surface wave tomography. This improvement in resolution will translate into 3D therefore providing new information about the velocity structure of the crust and upper mantle of our study area.