Abstract
The Eastern United States has a complex geological history and hosts
several seismic active regions. We investigate the subsurface structure
beneath the broader eastern United States. To produce reliable images of
the subsurface, we simultaneously invert smoothed P-wave receiver
functions, Rayleigh-wave phase and group velocity measurements, and
Bouguer gravity observations for the 3D shear wave speed. Using
surface-wave observations (3-250 s) and spatially smoothed receiver
functions, our velocity models are robust, reliable, and rich in detail.
The shear-wave velocity models fit all three types of observations well.
The resulting velocity model for the eastern U.S. shows thinner crust
beneath New England, the east coast, and the Mississippi Embayment. A
relatively thicker crust was found beneath the stable North America
craton. A relatively slower upper mantle was imaged beneath New England,
the east coast, and western Mississippi Embayment. A comparison of crust
thickness derived from our model against four recent published models
shows first-order consistency. A relatively small upper mantle low-speed
region correlates with a published P-waves analysis that has associated
the anomaly with a 75 Ma kimberlite volcanic site in Kentucky. We also
explored the relationship between the subsurface structure and
seismicity in the eastern U.S. We found earthquakes often locate near
regions with seismic velocity variations, but not universally. Not all
regions of significant subsurface wave speed changes are loci of
seismicity. A weak correlation between upper mantle shear velocity and
earthquake focal mechanism has been observed.