Magnitude 5+ Earthquakes – Global
5.7 Earthquake hits the Alaska Peninsula.
5.1 Earthquake hits southeast of the Loyalty Islands.
5.0 Earthquake hits Taiwan.
5.0 Earthquake hits Halmahera, Indonesia.
Slippery Clay at Fault in 2011 Japan Earthquake
Slippery clay that looks like scaly black dragon skin is the crucial clue needed to explain the 2011 Japan earthquake’s surprising impact, according to three studies published Dec. 5 in the journal Science.
The clay, which resists slipping just slightly better than a banana peel, lines the shallow part of the massive plate boundary fault offshore of Japan, where the seafloor jumped eastward by a staggering 165 feet (50 meters) on March 11, 2011. The enormous surge gave the ocean a giant slap, generating the destructive tsunami that killed more than 15,000 people.
The Tohoku quake was a magnitude 9.0, but it was like no subduction quake ever seen before. Before the 2011 earthquake, scientists thought subduction zones concentrated their energy deeply, where rocks are strong and plates can stick together between quakes. (Faults store energy between earthquakes kind of like springs, slowly squeezing until the boundary unleashes and everything rips apart.) But the Tohoku temblor was a surprise — the shallow part of the fault shifted twice as much as the deeper part. These soft, muddy rocks were expected to be too weak to store energy between earthquakes.
“We’d never seen such large slip happen at very shallow depth in a subduction zone before.”
The studies conclude the dragon-skin clay was the earthquake’s weak link. The slippery clay helped the plates slide so far during the 2011 temblor.
And because the clay layer is a distinctive marker found buried across the Northwest Pacific seafloor, scientists fear subduction zones near Alaska and Russia may also hide this clay. If so, their potential for powerful tsunamis could be greater than thought.