Tohoku Earthquake

First Posting | Summary
Posting Date: March 11, 2011, 9:00:00 AM

A massive earthquake struck near northeast Japan early this morning about 70-80 kilometers off the coast of Honshu, violently shaking dozens of cities along a 2,100-kilometer span of coastline and triggering a powerful tsunami that delivered crashing waves up to 10 meters tall to the northeast coast. Hardest hit by the tsunami was Miyagi prefecture, where residents had just 15 minutes to evacuate before the tsunami waves reached land. The waves swept cars, boats and debris inland; 200-300 people have been reported dead in the prefecture’s capital, Sendai (population 1,031,704 as of 2008). To the north, in Iwate prefecture, four villages were submerged and more than 300 homes collapsed. According to the United States Geological Survey (USGS), today’s earthquake had a moment magnitude of 9.1, revised from an earlier estimate of 8.9, and occurred at a shallow depth of 20 kilometers. It was the largest earthquake since recordkeeping in Japan began but reported ground shaking is less than the estimated ground shaking from the 1923 Great Kanto Earthquake (M7.9) because of its distance from the shore. The Japanese Meteorological Agency (JMA) issued a major tsunami alert for the east coast of Japan and reported it could not rule out the possibility of more tsunamis hitting coastal areas of the country. Maximum wave heights were reported at 10 meters in Fukushima prefecture and 7 meters in Miyagi prefecture. Tsunami warnings—some of which have been lifted—were issued in at least twenty countries following today’s initial wave. As of 14:32 UTC today, the Pacific Tsunami Warning Center (PTWC) indicated tsunami warnings were still in place for countries including Japan, Russia, Taiwan, the Philippines, Guatemala, El Salvador, Costa Rica, Nicaragua, Panama, Honduras, Chile, Ecuador, Colombia, and Peru, as well as the U.S West Coast and the state of Hawaii. Early this morning, the tsunami waves began impacting the Hawaiian island chain, hitting Kauai first. Though the PTWC does not predict the tsunami in Hawaii will be a major damaging event for the Hawaiian island chain, it will cause scattered damage. There were mass evacuations in Hawaii last night. In the last two days, Japan has been hit by a swarm of what are now considered foreshocks, beginning with an M7.2 earthquake on Wednesday, March 9, off the coast of Honshu, and three earthquakes greater than M6.0 on the same day. Today’s earthquake occurred in the subduction zone of the Japan Trench where the Pacific plate subducts under the Honshu island of Japan, part of the Okhotsk plate, at a rate of about 8 centimeters per year. The subduction zone at the Japan Trench is one of the most seismically active subduction systems on earth. On average, more than one earthquake of magnitude 7 occurs every decade in this subduction zone system, which is about 800 km long and located offshore of Honshu Island. Five earthquakes exceeding M7.5 occurred here in the last century, including M7.5 (1915) and 7.6 (1978) earthquakes in the same epicentral area as today’s quake, and the M8.0 Sanriku earthquake (1933), which generated huge tsunami waves. Today’s earthquake is the largest event ever recorded in the subduction zones surrounding the Japanese island. It may have ruptured over 400-450 kilometers of plate interface at the Japan Trench. Based on preliminary seismological data, the earthquake ruptured four of the five segments defined by Japanese seismologists. Earthquake insurance penetration in Japan is relatively low (ranging between 14 to 17 percent nationwide). About 70% of all residential construction is estimated to be of wood and about 25% of concrete. Commercial construction consists of more than 50% concrete, about one-third light metal or steel, and less than 10% wood. Residential structures in the region of Japan impacted by today’s quake are generally resistant to earthquake shaking. Some vulnerable structures do exist; they are comprised of non-ductile reinforced concrete frame and heavy wood-frame construction. At this time, a picture of damage from the quake, which was followed by more than ten aftershocks of at least M6.0, is still unfolding, though it is clear that at least minor damage occurred as far away as Tokyo, 373 kilometers from the epicenter. The following sections provide an overview of reported damage.

Human Cost:

• The death toll, expected to rise, stands at 200-300 bodies • Deaths reported in Miyagi, Iwate, Fukushima and Ibate prefectures • A ship carrying 100 people was swept away off the northeastern coast • At least 200 people were caught in a landslide in the province of Sendai

Property Damage:

• Building collapses, including a nursing home, reported in Fukushima prefecture; many collapses in Iwaki-city and Fukushima-city • Building collapses reported in Ibaraki prefecture • Three buildings collapsed in Kurihara-city in Miyagi prefecture • Building collapses in Chiba prefecture’s Narita city • Many residential homes washed out by the tsunami in Miyagi and Iwate prefectures • Oil tanks were damaged in Miyagi prefecture • More than 300 houses collapsed or were washed away in the coastal city of Ofunato

Fire Damage:

• Fire damage in the following prefectures, particularly at chemical plants, nuclear plants and oil refineries: Iwate, Miyagi, Akita, Fukishima, Ibaraki, Tochigi, Chiba, Tokyo and Kanagawa • Chiba prefecture: fire and explosion at an oil refinery and fire at a steel plant • Kanagawa: fire at a mid-rise building and a fire at an industrial facility • Fire at one office building in Tokyo

Infrastructure Damage:

• All highways closed around Kanto and Tōhoku • More than four million buildings were without power in Tokyo and its suburbs • Sendai airport inundated by the tsunami • Haneda airport stopped all departures • Narita airport stopped all departures • Ibaraki airport stopped all departures • The Japanese railway stopped all trains in Kanto and Tōhoku; other private railroads stopped trains • Cooling systems at the Fukushima Daichi nuclear power plant were damaged. Three-thousand residents near the plant were being evacuated early this morning. • Electronics giant Sony Corp. and carmaker Toyota shut down production at several of their plants The AIR earthquake team is analyzing the seismological data for this event as it becomes available and AIR will continue to provide information as events unfold.

First Posting | Downloads
Posting Date: March 11, 2011, 9:00:00 AM