36 aftershocks have been recorded in quake-devasated Japan since 6 a.m. ET Saturday, the largest of which measured magnitude 7.1. John Adams, a seismologist with Natural Resources Canada in Ottawa, says the earth could continue to rumble for months -- and not just around the area where Friday's magnitude 8.9 earthquake struck.
“Some of those aftershocks are quite close to Tokyo, so it's possible a magnitude 7 to 7.5 earthquake about 100 kilometres from Tokyo could happen,” he says. “That would be quite strong shaking for Tokyo.”
With strong aftershocks comes the possibility of more tsunamis. The tsunami triggered by Friday's quake spread across the Pacific Ocean over a period of about 20 hours, and seismic instruments may still detect it “sloshing around” for some time, Adams says. It's unlikely that an aftershock will cause another tsunami to go racing around the globe, but a large aftershock of magnitude 7.5 close to the coast could cause another tsunami in Japan.
“There is a possibility in Japan that a smaller tsunami could come onshore,” Adams says.
Assessing the global earthquake risk
With strong earthquakes occurring recently in Japan, New Zealand and Chile, other countries along the earthquake-prone Pacific “Ring of Fire“ are wondering if they could be next in line for a major shake.
Adams says earthquakes are nearly impossible to predict, but places that have not had a large earthquake for 100 or more years should always be on high alert.
“(They) do have to be concerned about quakes -- maybe not as large as the Japan one, but high sevens and eights,” he says, adding that includes California's San Andreas fault, which last ruptured in 1857.