All Shook Up

The earth shook around the world overnight, not only across the Indian subcontinent, but Greece, Japan, Mexico and here in the United States.

Fifteen minutes before a massive quake rocked the entire Indian subcontinent, a minor earthquake in northeastern Ohio cracked walls, set off alarm bells and knocked dishes off shelves.

Some residents said it felt like a train running through their homes.

"I thought a house blew up," homeowner P.J. Macchia said.

Within half an hour of the Indian quake, southwestern Greece felt a small temblor. Hours later Japan felt a small quake as well. No injuries were reported.

The Ohio quake occurred at 10:03 p.m. ET Thursday and lasted several seconds. It had a preliminary magnitude of 4.2 on the Richter Scale, meaning it was strong enough to cause minor structural damage, said Michael C. Hansen of the Ohio Seismic Network.

The National Earthquake Information Center said the quake was centered in Lake Erie, in the same area where a slightly milder quake was reported last week.

Ohio has had 120 earthquakes in the past 200 years, most of them minor.

In Greece, the undersea temblor struck at 10:37 p.m. ET off the coast about 115 miles west of the capital of Athens, with an estimated magnitude of 4.1 on the Richter Scale.

The Japan quake struck at 3:42 a.m. ET and was centered near an island between southern Japan and Okinawa. Japan's Meteorological Agency says there is no danger of a tsunami - a tidal wave that can be triggered by undersea earthquakes or volcanoes.

In Mexico, a magnitude-5 quake shuddered through southern coastal areas at 8:19 a.m. (11:19 a.m. EST). Centered on the coast of the southern state of Oaxaca, the quake was felt as far away as Mexico City, about 220 miles to the north, where some buildings swayed slightly.

In the coastal Oaxacan municipality of Jamiltepec, the quake cracked walls and left minor fractures in the structures of about 200 houses, city hall and the local church, Mayor Martin Echeverria said.

The number of quakes making the news Friday, and the recent major quake in El Salvador and minor tremors in Los Angeles and New York City, raise the question of whether the seismic events are related.

'There is no relation," Mary Lou Zoback, chief scientist with the U.S. Geological Survey's Earthquake Hazards Program, told CBSNews.com. "The earth's surface is broken into a number of different plates. These earthquakes were on different quakes."

Those massive plates that make up the earth's crust glide on the molten material than forms the lower layers of Earth. Sometimes, as two plates moving in opposite directions press or grind against one another, pressure builds up. An earthquake happens when one or both plates slip suddenly, sending ripples of force outwar.

As for the number of quakes making headlines Friday, Zoback said, "We have that everyday." Indeed, experts say they routinely track 50 minor quakes a day.

It is possible that the minor quakes in Japan, Greece and elsewhere are "foreshocks," which precede a larger quake. But scientists can't tell — yet.

"We usually don't recognize it as a foreshock until we have a bigger earthquake," said Zoback. "As it turns out, very few earthquakes have foreshocks."

"If they did, we'd be much better at predicting earthquakes," she said.

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