My research interests center on understanding why earthquakes occur in continental, intraplate seismic zones. I approach this interesting problem using local travel time tomography to investigate the seismic velocity structure of the crust hosting the seismic activity. To date, P wave and S wave velocity models and Vp/Vs ratios have been determined for four intraplate zones: the Charlevoix seismic zone located near Quebec, Canada, the 2001Bhuj India aftershock zone, the eastern Tennessee seismic zone (ETSZ) and the New Madrid seismic zone (NMSZ). A common observation in all four zones is that strong velocity contrasts are present and that these contrasts appear to control the distribution of seismicity. The results suggest that earthquakes in intraplate seismic zones tend to occur in rocks where strain energy is concentrating. The Vp/Vs results for the NMSZ are particularly interesting. Low Vp/Vs ratios are associated with the main branches of seismicity. The cause for the low ratio values remains an open question. I am also using gravity and magnetic data to investigate crustal structure associated with the ETSZ. Results suggest that the seismicity is associated with a Grenville-age suture zone that juxtaposed crustal masses with different lithological properties. Ongoing research projects involve application of double-difference tomography to determine source locations and velocity structure in the ETSZ and the NMSZ.
Langston, C., Powell, C., and Patterson, G. (2002), Strong ground motion in the New Madrid seismic zone and lifeline vulnerability, Proceedings of the Fourth China-Japan-USA Trilateral Symposium on Lifeline Earthquake Engineering, Qindao, China, edited by Y. Hu, S. Takada, and A. S. Kiremidjian.
Vlahovic, G., and Powell, C. A., Three-dimensional S-wave velocity structure and Vp/Vs ratios for the New Madrid seismic zone (2001), Jour.Geophys. Res. v. 106, 13,501-13,514.
Graduate Student Opportunities: Please contact me for specific projects related to intraplate seismicity, local and teleseismic velocity inversion, and potential field projects.