(CNN)Several million earthquakes occur annually, but most are unnoticed because they're so small, the U.S. Geologic Survey says.
Ecuador and Japan earthquakes: Are they related?
But three recent earthquakes -- on Thursday and Saturday morning in Japan and Saturday night in Ecuador -- have gotten lots of attention because of the great destruction.
Here are five things to know about those quakes.
It's way too early to tell, said Paul Caruso, a geophysicist with the U.S. Geological Survey.
"It's one day after the Ecuador earthquake and two days after the Japanese earthquake, so no real research has been done on these quakes as far as they're being connected," he said Sunday.
"Usually we don't think earthquake are connected across the ocean," Caruso said, but there's ongoing research in "remote triggering," the idea that a big quake can cause another quake a long distance away.
The distance between Japan and Ecuador: 15,445 kilometers, or about 9,590 miles.
Both quakes occurred in this horseshoe-shaped area the National Geographic Society defines as "a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean."
It may seem more than coincidental that the quakes occurred a few days apart. But it's also true that the large majority of the world's earthquakes -- about 90% -- occur in the Ring of Fire, per the National Geographic Society.
The Ecuador earthquake was almost 16 times stronger than the Saturday morning quake in Japan.
That figure comes courtesy of the "Try It Yourself" calculator on the USGS website. Ecuador was hit by a magnitude-7.8 quake, Japan by a magnitude-7.0 quake. Plug those numbers into the calculator, and you come up with 15.848. (The Thursday Japan quake was magnitude-6.2.)
If you're a math geek and want to see the formula, it's on the USGS website.
No. On January 31, 1906, a magnitude-8.8 quake occurred off the coast of Ecuador and Colombia, generating a tsunami that killed 500 to 1,500 people, according to the USGS website. The quake was first measured at magnitude-8.2.
On May 14, 1942, a magnitude-7.8 earthquake occurred 43 kilometers south of the site of the recent quake.
The Saturday quake is the deadliest to hit the nation since March 1987 when a 7.2-magnitude temblor killed 1,000 people, according to the USGS.
Quakes with a magnitude between 7.0 and 7.9 occur about 15 times a year, according to information collected by the USGS over the decades.
The bigger ones -- magnitude-8 and over -- happen about once a year.