No injuries or major damage was reported, and the light quake wasn't even noticed by some residents living close to the epicenter, near Karnes City. Yet small vibrations felt in San Antonio did cause occupants to briefly evacuate a downtown federal building as a precaution.
The quake struck at 7:24 a.m. The U.S. Geological Survey said it was the largest earthquake on record for the area, surpassing a magnitude-4.3 shock recorded in 1993.
Thursday's earthquake occurred in a zone that has shaken in the past. From 1990 to 2006, at least a dozen small quakes rattled this region.
"It's an area where we've seen events before," said U.S. Geological Survey seismologist Susan Hough in Pasadena, Calif. "So it's not a big surprise."
Glynda Martinez, an associate municipal judge in Karnes City, said she thought a strong gust of wind or a tractor-trailer driving by was rattling dishes in her kitchen.
"When I saw my grandson this morning the first thing he told me was, `Grandma, our trailer house was shaking,"' said Jaunita Munos, school secretary for the Pawnee school district.
Small earthquakes in Texas are not exceptionally rare, but are seldom felt in this area. The last one recorded around Karnes County was in January 2010 and had a magnitude of 2.6, which is too small for many people to feel.
A September earthquake in West Texas had a 4.4 magnitude and was centered just north of Abilene.
The largest Texas quake occurred in 1931 when a magnitude-5.8 temblor struck near Big Bend. Adobe buildings were severely damaged and brick chimneys toppled, but there were no deaths.