More aftershocks feared after M6.5 quake in southwestern Japan

More than 130 aftershocks were recorded by Friday evening after the magnitude-6.5 quake hit Kumamoto Prefecture at 9:26 p.m. the night before, the third-highest number of aftershocks following quakes of similar or stronger intensity since 1995, the agency said.

The initial quake originated at a depth of around 11 kilometers in Kumamoto Prefecture. The agency said strong aftershocks often occur after shallow earthquakes because the earth's crust tends to be more brittle nearer the surface.

Thursday night's quake registered a maximum 7 on the Japanese seismic scale in the town of Mashiki, the first time that level has been recorded on the island of Kyushu, the agency added.

Nine people died in the quake and over 1,000 were injured.

The agency said there is a 20 percent probability of an aftershock measuring lower 6 or higher on the Japanese seismic scale over the three-day period starting at 4 p.m. Friday, and a 40 percent likelihood of one registering higher 5 or greater.

Already an aftershock measuring upper 6 on the Japanese seismic scale struck at three minutes past midnight, and another was recorded as lower 6. Two aftershocks were recorded at lower 5 and 16 at 4.

With rain forecast for the area over the weekend, ground softened by the quake is at risk of giving way to landslides.

In March 2013, the agency began measuring the intensity of ground movement during earthquakes with a long duration. During the upper 6 aftershock in Kumamoto Prefecture, the maximum level 4 on that scale, which indicates ground movement is too intense for people to stay standing, was recorded for the first time in Japan.

According to the agency, the initial quake and subsequent aftershocks occurred along a "strike-slip" fault, where two adjacent areas move against each other horizontally.

A government earthquake taskforce held a special meeting Friday to evaluate the connection between the quake and known fault lines in the area.

Opening the meeting, science minister Hiroshi Hase called on the 19-strong team to "work toward figuring out the mechanism (behind the quake) based on the current data."

"With many active faults still undiscovered, it would not be surprising for a similar quake to occur anywhere in the Japanese archipelago," said Katsuhiko Ishibashi, professor emeritus of seismology at Kobe University.

"There is no guarantee that further shaking won't be stronger than that of Thursday night, so rescuers and evacuees need to be extremely careful," Ishibashi said.

The damage from Thursday evening's quake is concentrated in a narrow area with many older houses that lack seismic reinforcement, reminiscent of the 1995 Great Hanshin Earthquake that killed about 6,500 people and devastated Kobe and surrounding areas in western Japan, said Yoshiteru Murosaki, head of the Education Center for Disaster Reduction at the University of Hyogo in Kobe.

According to the National Research Institute for Earth Science and Disaster Resilience, the maximum acceleration in the initial quake was measured at 1,580 gal.

This is far above the acceleration at the earth's surface due to the planet's gravitational pull, which is defined as an average of 980 gal.
A gal, named after Galileo Galilei, is defined as 1 centimeter per second squared.