Some felt earthquake, others didn't
Although several Belen residents who live near the presumed epicenter of Friday's earthquake felt their houses shake, rattle and roll, refined seismic data now place the epicenter several miles to the northwest.
The earthquake, originally recorded at 3.5 magnitude by the U.S. Geological Survey, the federal agency that measures seismic activity, has also been downgraded to 2.8 magnitude by New Mexico scientists.
"We produced a refined location today (that) puts the earthquake about seven miles northwest of the USGS location," said Richard Aster, a professor of geophysics at the New Mexico Institute of Mining and Technology, in an e-mail to the News-Bulletin on Monday. "The local duration magnitude was 2.8 (I think that the USGS magnitude was overestimated)."
Several people who live near the original epicenter site, a vacant field between Main Street and Don Felipe Road in north Belen, described the brief jolt in vivid terms. One family even ran outside.
Cathy Fragua, who lives near Mesa Road, at first thought the loud bang and shock might have been caused by two trains hooking up.
"It was pretty loud," Fragua said, adding that she was surprised by the intensity of the noise.
Fragua, her husband and their 8-year-old daughter ran out of the house, but later — somewhat sheepishly — they would laugh about it.
Her husband thought something had happened to pipes under their house, she said.
"He was really worried," she said.
It was their little girl who first asked, "Was that an earthquake?"
"No, of course not," answered her parents.
Fragua said the earthquake lasted only a few seconds but "definitely shook our house."
She wasn't the only one who thought the quake might have been railroad related.
"That was an earthquake!" responded Trinity Ortega when asked about the jolt. "That's kind of cool.
"But seriously," he continued, "it literally just lasted two seconds. It gave everyone's house around here a good shaking. It felt like the trains were stopping."
Apparently no one suffered any injuries or reported property damage. Some laughed about their reactions afterward.
"I just thought my daughter was messing around downstairs," said Elaine Luchette, who was upstairs in her two-story house on Abby Lane at the time. She said the house shook, but not long enough to scare her.
Two men, an uncle and nephew who live on Don Felipe Road close to the presumed epicenter, had a decidedly different reaction. Both responded in exactly the same way when asked about the quake.
"Really?" they said incredulously. "An earthquake? I didn't even know about it."
Aster, a scientist with the Geophysical Research Center and Department of Earth and Environmental Science at NMIMT in Socorro, described the earthquake as an isolated event.
"We have seen no significant aftershocks at this point," he said. "We are studying it today for more detailed information using our seismographic data recorded here in New Mexico."
He provided the News-Bulletin with a seismic printout recorded near Lemitar that clearly shows the earthquake striking the area less than a minute before 7 p.m. Friday. The printout also showed a few tiny aftershocks that Aster said he and his colleagues "are examining in detail."
Other signals visible on the printout were the result of the ground shaking from trains throughout the day, which indicates just how sensitive the seismographs are.
Although New Mexico does not lie over the juncture of tectonic plates — the shifting of which often causes earthquakes — there are faults lining the Rio Grande Valley, which interact with the inflating Socorro Magma Body, Aster said. This produces elevated seismic activity.
Friday's earthquake was outside the area generally considered part of the Socorro Magma Body, but not far. Over the past few decades, the general area has been a frequent producer of small earthquakes.
Earthquakes of magnitude 2.5 to 3 are generally the weakest felt by humans. A 2.8 is considered mild.
The USGS received 13 calls from the public following the earthquake, including one from Rio Rancho and two from Albuquerque. Most of the calls, however, came from closer to home: six from Belen, three from Los Lunas and one from Bosque Farms.
Originally, the epicenter was placed at six kilometers below the surface of the earth at 34.67 degrees north latitude and 106.67 degrees west longitude.
Meanwhile, three earthquakes shook North Texas over the weekend. The USGS said a magnitude 2.1 quake occurred Sunday night near Dallas. A day earlier, 3.4 and 3.1 magnitude quakes jolted the same area, with no reports of damage or injury.
Most earthquakes in New Mexico are concentrated in the Rio Grande Valley between Socorro and Albuquerque. About half of the mild to moderate earthquakes that occur in the state are centered along the river.
In December 1935, Belen experienced a series of earthquakes. In one, loud subterranean sounds accompanied a strong shock that cracked the brick wall of an old public school building. People also reported fallen plaster and objects knocked off shelves.
The area around Los Lunas was affected by a series of earthquakes in 1893 that lasted about three months. Some were felt as far away as Sabinal in Socorro County.
The earliest reported earthquake in New Mexico struck near Socorro in 1855. In the years that followed, Socorro was struck by numerous low to moderate intensity earthquakes. Most caused little or no damage and were felt over a small area.
However, from July 1906 to well into 1907 the area was affected by shocks almost daily, including one that knocked down some adobe walls and cracked others.