Authorities said neither quake caused major damage or injuries. The tremor late Wednesday afternoon was the third strong one to shake Mexico City in as many weeks and rattled the nerves of weary residents.
The U.S. Geological Survey said Thursday's 6.9-magnitude quake hit the waters between the Baja peninsula and the northern state of Sonora at 12:15 a.m. local time.
People in the city of Hermosillo woke up as their beds swayed and their ceiling fans shook. Luis Enrique Cordova, director of emergency services in Sonora, said confused residents clogged the phone lines of the civil protection office in Hermosillo, capital of the state and home to some 700,000. But Cordova said no major damage had been detected in the region.
"I was on my bed, leaning against the wall, and the fans kept moving non-stop, side to side," said Carlos Morales, a teacher in Hermosillo.
The temblor was centered 82 miles (133 kilometers) northeast of Guerrero Negro and 133 miles (215 kilometers) west of Hermosillo. It hit some 6.4 miles (10.3 kilometers) below the surface.
Hours earlier, a 6.4-magnitude quake struck a sparsely populated area in the mountains of western Michoacan state and caused multi-story buildings to sway more than 200 miles (322 kilometers) away in Mexico City.
A 7.4-magnitude earthquake on March 20 was felt strongly in the nation's capital, and it damaged hundreds of homes and killed at least two people near the border between Guerrero and Oaxaca states. Mexico's seismological service said that quake has been followed by close to 400 aftershocks, including one of magnitude 6.0 that also rocked the capital.
Shortly after Wednesday's temblor hit social networks began buzzing with comments of scared residents.
"We just had another earthquake, this is damn scary," wrote a Twitter user.
On Facebook, doomsday prognosticators posted cartoons of Mayan characters with slogans that read "we apologize for the inconvenience, we are working," in
reference to the belief that the Maya predicted the end of the world for December 2012.
A quake alert application for Blackberrys that Mexico City's government touted last week did not work Wednesday. Mexico City Mayor Marcelo Ebrard said the alert system so far is set up only for quakes centered in the southern states of Guerrero and Oaxaca. He said it will begin to work for any tremors in Michoacan in the next few days.
Scientists said the quakes shaking Mexico have not been triggered by each other and are not signs of impending doom. They say the tremors are simply the result of having three tectonic plates come together off Mexico's Pacific coast.
Don Blakeman, geophysicist with the U.S. Geological Survey, said quakes that hit in different locations are not related and it's simply coincidence that they happen so close together.
"Mexico, Japan, Indonesia and California are seismic reactive areas and they are always going to have earthquakes," Blakeman said. "Places like Mexico, California and Japan are really beautiful places to live because the tectonic plates keep moving and they make mountains and beautiful seascapes, but earthquakes come with this beautiful sceneries and that's the way it is."
Victor Espindola of Mexico's national seismological service said the country is hit with hundreds of small-magnitude earthquakes every year. He said that on average, there is a quake of magnitude 5.0 or more each month.
"What we're experiencing is nothing extraordinary," he said.
That's no consolation for Mexico City residents who still remember a devastating magnitude-8 earthquake that hit in 1985 and killed an estimated 9,000 people and flattened parts of the capital.
"I don't remember having felt so many earthquakes so close together," said Paola Medina, a 26-year-old insurance saleswoman who works on the fourth floor of an office building on the city's main Reforma Avenue. She was born a month after the 1985 quake and grew up hearing about it.
"I will never get used to that horrible sensation of uncertainty you feel when a quake hits," she said.
