Earthquake Hit Texas Near San Antonio, Says USGS

A magnitude 4.5 earthquake has rattled southern Texas in the vicinity of San Antonio, the U.S. Geological Survey (USGS) reported. The quake struck at 9.26 p.m. on Wednesday, at a depth of about 2.3 miles beneath its epicenter on the surface, which lay roughly 12 miles east-northeast of Falls City. The main shock was followed a few hours later by a magnitude 2.6 tremor 10.5 miles south-southeast of the city of Stockdale. According to the USGS website, the Falls City quake is likely the main shock of an earthquake sequence that began with four other smaller tremors (with magnitudes between 1.6–2.9) in the first couple of weeks of January. The magnitude of earthquakes is measured on a logarithmic scale. This means, for example, that the amplitude of the seismic waves at a given distance from the epicenter is 10 times larger for a magnitude 5 quake than they would be for a magnitude 4 one. Around 500,000 quakes with a magnitude between 2.5 and 5.4 occur around the globe each year—the tremors from which are often felt, but typically cause only minor damage. The USGS website has logged 642 reports of people feeling the Falls City quake—mostly in the immediate vicinity of the epicenter and east of San Antonio, but also as far north as the area around the city of Killeen. Reports of Texas residents feeling the quake have also been posted to X. User @remi_ur_angel, for example, asked: "yall feel that earthquake?? im right near down town san antonio", while @erotescry posted: "Um. Just felt my first earthquake ever and I live in San Antonio 😭 hello???"

Earthquakes occur as a result of the constant—but, to us, imperceptibly slow-paced—movement of tectonic plates across the Earth's surface. Most quakes occur near to the boundary of these plates, the result of the slow buildup of stress in the crust. When this stress overcomes the strength of the rock to create a fault, or the friction along existing fault planes, the ground slips—releasing waves of energy. Being located far from the boundaries of the North American Plate, Texas is not a state where, from a tectonic point of view, geologists would expect to see much seismic activity. Tremors can occur within the center of tectonic plates, the result also of tectonic stresses and the development of zones of weakness in the crust. However, seismologists have linked an increase in Texan quakes with oil and gas operations, which can affect the stress state of the subsurface.

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