COLUMBIA, S.C.—Yet more earthquakes have struck near South Carolina’s capital city, the ninth and tenth in a series of rumblings that have caused geologists to wonder how long the convulsions might last, or if they could possibly portend future, more serious seismic activity. Early Wednesday, a 2.6-magnitude earthquake struck near Elgin, about 25 miles northeast of Columbia, according to the U.S. Geological Survey. It was measured at a depth of 0.5 kilometers, officials said. About 7 hours later, another earthquake hit the area, this one with a magnitude of 1.5, according to officials. That area, a community of fewer than 2,000 residents near the border of Richland and Kershaw counties, has become the epicenter of a spate of recent seismic activity, starting with a 3.3-magnitude earthquake on Dec. 27. That quake clattered glass windows and doors in their frames, sounding like a heavy piece of construction equipment or concrete truck …