6.9 Magnitude Earthquake off Okinawa; What Holds Clues to Massive Quakes?

An earthquake of 6.9 magnitude was recorded off the northwest coast of Okinawa, Japan, at noon Tuesday, according to the U.S. Geological Survey. The quake was measured at a depth of 209.5 km (130.2 miles) and its epicenter was 215 km (133 miles) northwest of Naha, Okinawa, and 500 km (310 miles) east northeast of Taipei, Taiwan.

The Pacific Tsunami Warning Center did not issue any alerts, saying the quake did not generate any tsunamis. An Associated Press report stated that there were no reports of damages or injuries.

The northeastern region of Japan was hit by a 9.0 magnitude quake on March 11, which left nearly 23,000 dead or missing. It also cut power to the Fukishima nuclear power plant; the resulting meltdown was one of the most severe in history.

Does the Costa Rican Sea Floor Hold Answers?

According to scientists, pieces of rock chipped off the floor of the Pacific Ocean off Costa Rica could explain what made the March 2011 quake so intense. Both Japan and Costa Rica fall within the Ring of Fire around the Pacific, making both nations among the world's most seismically active areas.

Scientists believe the Ring of Fire to be formed by volcanic arcs and oceanic trenches surrounding the Pacific Basin; a region often struck by quakes and volcanic eruptions.

Researchers have collected sediment cores (cylinders of earth drilled out from the ground) from almost a mile deep, off the Costa Rican coast. An examination of these cores reveals comprehensive records of about 2 million years of tectonic activity, along a nearby seismic plate boundary; this marks the location where one plate dives under another, making it a subduction zone. According to Insidecostarica, it could have been the crack of a subduction zone that generated the March 2011 earthquake in Japan.