EL CENTRO — A strong earthquake, measuring 6.3 on the Richter scale, jolted the Imperial Valley early Tuesday morning, injuring 94 people in the United States and Mexico and damaging some structures. It came just 12 hours after a quake of slightly smaller magnitude struck the same area.
Across the border in the town of Mexicali the Red Cross said a mother and child were killed when they fled a downtown factory during the temblor and were struck by an automobile.
Fifty people were treated for injuries in Mexicali and 44 in Imperial County. Most of the injuries were minor.
The quake was the strongest in California since the Coalinga earthquake of May 2, 1983, which was 6.7 on the Richter scale. The quake hit at 5:16 a.m. and was felt as a rolling motion across Southern California and as far east and north as Phoenix and Las Vegas.
The epicenter of the shock, like the 6.0 quake that struck Monday evening and its numerous aftershocks, was in a lightly populated desert area. Tuesday's epicenter was 14 miles southwest of the small community of Westmorland in Imperial County.
Its distance from populated areas kept damage and injuries down compared to the severe disruption caused by the Oct. 1 Whittier Narrows earthquake, which was only about half as strong but was centered in heavily populated parts of the San Gabriel Valley just east of Los Angeles.
Still, authorities reported that 20 people were treated for various injuries at the El Centro Regional Medical Center and another 20 at El Centro's Valley Urgent Care Center. Another four injuries were reported outside El Centro. Broken bones, sprains, cuts and some mild heart attacks were reported.
The woman reported killed in Mexicali was identified as Carmen Garcia Munoz. The child was not immediately identified.
Officials in the U.S. border town of Calexico said that a furniture store's brick wall collapsed on several automobiles and there was damage to other buildings in the downtown area. Part of a brick wall collapsed on a car belonging to a waitress who had just shown up for her job at an El Centro cafe.
Outside Calexico, mobile home dweller George Jenkins said that when the quake struck, his trailer "started rolling like a baby's cradle. . . . My dogs were barking outside. I woke up my wife and we ran."
Westmorland, population about 1,500, was the town nearest the epicenter.
"This one this morning was the freakiest I've ever been in," said Westmorland resident Donna Ginnis. ". . . My whole bedroom was spinning. The quake knocked our bedroom door to the floor. My little boy was petrified."
An official in Mexicali said that 650 people were evacuated from 35 buildings that appeared to have suffered structural damage. This included about 200 from the 9-year-old municipal hospital, and others from two other hospitals and the badly damaged City Hall. The Mexican army was called in to provide security and schools were closed for the day. A flower shop was destroyed by fire.
At the municipal hospital, Dr. Antonio Gomez Vera, the director, said: "We had several patients who became very anxious and hysterical, but we still evacuated the entire hospital in about 30 minutes. . . . Our biggest challenge right now is giving these people food and drink."
Caltech seismologists said the main shock was on the Superstition Hills Fault northwest of the Imperial Valley and that a 4- to 7-inch horizontal displacement was found on Imler Road, southwest of Westmorland.
The Superstition Hills Fault is believed to be part of the San Jacinto Fault system.
Monday night's 5:53 p.m. quake originally had been assessed at 6.2 on the Richter scale but was downgraded to 6.0 on further evaluation and reclassified as a foreshock Tuesday.
Centered about six miles northeast of the epicenter of the main shock, it occurred on a previously unrecognized fault that runs southwest to northeast under the southern edge of the Salton Sea and perpendicular to the Superstition Hills Fault.
Caltech seismologists called the two-day episode, which also was marked by 5.4 and 5.5 shocks as well as more than 30 above 3.5, the Superstition Hills sequence. Seismologist Kate Hutton said it was a "very rich aftershock sequence" and cautioned, "They'll be feeling shocks for weeks out there."
There were "literally thousands" of aftershocks above magnitude 2, Hutton added.
Hutton noted that the geological forces that powered the quake are the same ones that pulled Baja California away from Mexico to form the Gulf of California.
Tuesday's quake caused numerous power and telephone outages and gas line breaks in an area extending from Westmorland through El Centro and Calexico into Mexicali.
Authorities estimated that 65,000 households and business lost power after the early morning shock, but 95% of the outage was corrected within 20 minutes, according to a spokesman for the Imperial Valley Water District.