Are recent quakes a warning?
From Brian Todd
WASHINGTON (CNN) -- At Hollywood Park racetrack, the horses didn't cause the commotion.
"That wasn't thunder, ladies and gentleman, that was the ground shaking!" the announcer said as an earthquake struck Thursday.
In Inglewood, Yucaipa, and throughout Southern California, residents dodged injury and serious damage - this time.
"We do have earthquake insurance and I can say that I'm really glad that we have it," says one Yucaipa woman.
Seismologists cannot tell her if she'll need that policy in the future but they're keeping a close eye on Yucaipa, where Thursday's 4.9-magnitude quake hit between two plates of the San Andreas Fault.
Add that to three other quakes in California or offshore, including an aftershock registering 6.6, a massive and deadly earthquake that rocked northern Chile, another in a series of tremors in the Aleutian Island chain off Alaska, plus a moderate earthquake in the tsunami-ravaged Aceh province, in Indonesia, which all occurred this week.
Are they connected?
"They are really not connected in any sort of obvious way except that the earth is a dynamic earthquake-producing body. All around the Pacific we have earthquakes every week," says Michael Blanpied of the U.S. Geological Survey.
Experts say many of these quakes are on different fault lines.
But they're also in the so-called Ring of Fire in the Pacific Rim. And seismologists say when an earthquake occurs it relieves geological stress in one place and builds that stress in another.
In California, events in this kind of succession revive the inevitable question: Is that massive quake predicted along the San Andreas Fault on the way?
"'The Big One' is always on the way in California because we know that the faults in California are capable of producing great earthquakes that will do considerable damage. ... However, the occurrence of these moderate earthquakes this week does not mean in any kind of obvious way that we understand that there is a 'Big One' immediately on the way," says Blanpied.
Some experts are more worried about the Sumatran coast in Indonesia, the general area where the tsunami hit last December.
That event, plus another massive offshore quake nearby in March, they say could foreshadow an earthquake in that region that could get up to a magnitude 9.0.