Earthquake Relocations in the Eastern Tennessee Seismic Zone: The Control of Ancient Basement Structure on Present-Day Seismicity in an Intraplate Setting
Abstract
We present three-dimensional P- and S-wave (Vp and Vs) velocity models and hypocenter relocations for the active eastern Tennessee seismic zone (ETSZ) based upon arrival time data from more than 1000 local earthquakes. The most striking result is the change in hypocenter density on either side of a pronounced, NE-SW trending, linear magnetic anomaly; many more earthquakes occur SE of the magnetic lineament than NW. The magnetic anomaly is part of the extensive New York - Alabama (NY-AL) magnetic lineament and is attributed to a structural boundary in Grenville basement rocks. A distinct change in crustal velocity also occurs across the magnetic lineament; high Vp and Vs (relative to a 1D starting model developed specifically for the seismic zone) occur to the SE and low Vp and Vs occur to the NW. This strong velocity contrast persists over the depth range 4 - 12 km in the Vp model and 4 - 24 km in the Vs model. The strongest velocity contrast corresponds to the steepest portion of the magnetic gradient defining the NY-AL lineament and with the greatest number of earthquakes. Relocated hypocenters suggest the presence of vertical, NE trending faults, in agreement with previous studies of focal mechanism solutions. The distribution of relocated hypocenters together with the velocity solutions attest to the strong influence that Grenville basement structure has on present day seismicity.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.S21B2025P
- Keywords:
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- 7230 SEISMOLOGY / Seismicity and tectonics