The Hot Springs, Virginia area is the largest concentration of thermal springs in the eastern United States. The region's anomalous geophysical and geological character is indicated by: (1) apparent low heat flow, (2) an “earthquake shadow” of considerable extent, (3) great crustal thickness, (4) a structural transition zone between the central and southern Appalachians, and (5) the presence of Eocene igneous intrusives.
As a first step toward geophysical study of the area a 10-day reconnaissance microearthquake survey was conducted. Seven sites were occupied to collect a total of 438 hr of low-noise data. A 4-day swarm of 43 events was recorded at one site (20 km northeast of the Hot Springs) while the other six sites exhibited no activity. Continuation of this type of study is needed to define the seismic regime of this important area.