Magnitude 7.7 earthquake off Sanriku brings a tsunami to Kuji

An earthquake measured at magnitude 7.7 struck off the coast of Sanriku, Japan. A tsunami followed. The wave was reported at 80 centimeters, or 2.6 feet, in Kuji, in Iwate Prefecture. The shock and the wave were reported on April 20.

Magnitude measures the energy of an earthquake. A 7.7 shock is a major earthquake. Sanriku is the coastal region of northeastern Japan along the Pacific, a stretch long associated with offshore quakes. A tsunami is a sea wave set in motion when an earthquake disturbs the ocean.

Eighty centimeters is a wave height of a little under a meter. That is lower than the catastrophic tsunamis that have hit the same coast in other years, and the report does not compare it with those events or give a death toll. Kuji is the town in Iwate where this height was reported. The figure is the height given for that place, not a claim about every harbor.

Iwate Prefecture is one of the prefectures of the Tohoku region on Honshu. An offshore epicenter can produce a tsunami even when the strongest shaking is at sea. The report does not give the depth of the quake or the exact distance from shore. It gives the magnitude, the Sanriku location, and the wave at Kuji.

Tsunami warnings and evacuation orders are the usual official response to a shock of this size off Japan. Those steps are not itemized in the brief report. No count of damaged houses is included. The established facts are the magnitude, the coast, and the 80-centimeter wave.

A magnitude 7.7 earthquake off Sanriku produced a tsunami that reached about 80 centimeters in Kuji. The town is in Iwate Prefecture. No casualty figure was attached to this first account. The quake was reported on April 20.