The answer to that would be "the ground" for some folks on the southwestern fringes of our viewing area, in particular around Richmond and Anson counties, where two minor earthquakes have been recorded in the past three days, the second occurring around 1:44 am this morning, the first at 7:22 am on Friday Sep 22nd. No damage or injuries have been reported with either quake, both having very similar magnitudes of 3.6 on Friday and 3.5 earlier today. The quakes were in the same general area, but their hypocenters were several miles apart and located about 3 miles below the surface. The epicenters of the two quakes, those being the points on the surface directly above the hypocenters, were about 55 miles west-southwest of Fayetteville on Friday and about 59 miles southwest of Fayetteville today.
These quakes were located in an area that has experienced similar magnitude tremors on rare occasion in the past, but are not within any of three more concentrated areas of more frequent earthquake occurrences in our general region. These somewhat more active areas are known as the East Tennessee, Central Virginia, and Charleston Earthquake Zones, respectively, and you can see them on a map that is part of a good summary of earthquake activity around our region provided by the NC Geological Survey.
For more details on the two recent earthquakes just south of the border, see this map from the US Geological Survey. Clicking on the squares that indicate the location of each quake will bring up a page with all the measured parameters. Those pages also have a "did you feel it?" link. Clicking that will show a "shake map" indicating where the quake was felt and with what intensity. Some of you may recall a magnitude 4.5 quake on Dec 9, 2003 that occurred in the Central Virginia Zone northwest of Richmond. That one was felt as far south as central parts of our viewing area - you can see an intensity map for that event here.
Finally, you can always quickly check for recent earthquakes worldwide at this USGS site.
