Strong earthquake aftershock strikes northeast Japan

by Artemis on April 7, 2011

A significant aftershock has struck the northeast of Japan within the past hour. The earthquake was said to be between 7.1 and 7.4 on the richter scale, to put that into perspective it is about 1,000 times less powerful than the earthquake on the 11th March in the same region.
However, tsunami warnings have been issued for areas on the northeast coast of Japan, including Sendai area which was one of the worst affected by the 11th March quake and tsunami and also Fukushima where the stricken nuclear power plant is situated.

Residents of the area have been told to evacuate to higher ground and to expect a tsunami of around 1m in height. There are unconfirmed reports of damage to another nuclear power station at Onagawa in Miyagi prefecture.

Ground shaking was strong on the coast nearest the quake and the aftershock was felt in Tokyo. It’s unlikely that shaking would be strong enough to worry catastrophe bonds as they are targeted on Tokyo area incidents.

Map showing the location and ground motion from the USGS below. USGS information available here. We will update this article as further information becomes available.

Update: There has been no news of any tsunami damage at this time. This aftershock struck at 11.30pm local time which will make it difficult for the authorities to confirm whether a tsunami indeed struck land until daylight tomorrow. The nuclear power station at Onagawa has not sustained damage according to NHK but the power has been switched off (which happens automatically after large quakes) and it is running on back-up generators (as are some other nuclear power stations in the northeast). This is a precautionary move which is automated.

There are some early reports of blackouts in coastal areas and a fire in Yamagata area. However, due to the damage suffered on the 11th March, any insured losses from this aftershock are expected to be limited as the area is already so devastated.

Update 2: The Japan Meteorological Agency reports that all tsunami watches and warnings are cancelled.

Update 3: The New York Times has a report regarding Japan’s nuclear power plants after this aftershock.

Update 4: The BBC reports that at least 3 people died in the quake and over 100 injuries were reported. It’s safe to assume that there has been some damage to buildings in the northeast. Reuters reported that the Onagawa nuclear plant had developed a water leak/spill (potentially coolant?) but that radiation levels were normal and there was no need for concern. Approximately 2.8m people have been without power overnight in northeast Japan.

Update 5: Risk Management Solutions have issued a report on the 7.1 magnitude aftershock which occurred yesterday:

On Thursday, April 7 (11:32pm local time) a magnitude Mw7.1 earthquake occurred offshore the east coast of Honshu, Japan – a powerful aftershock of the Mw9.0 earthquake on Friday, March 11.

The United States Geological Survey (USGS) has reported a fixed focal depth of 30.4 miles and an epicentral location around 40 miles east of the epicenter of the Mw9.0 earthquake, and 41 miles east of Sendai, Japan, the area worst affected by the Mw9.0 earthquake. Shaking from the earthquake was felt as far away as Tokyo, 205 miles south-southwest of the Mw7.1 aftershock.

The Japanese Meteorological Agency issued a local tsunami warning for Miyagi Prefecture with an expected wave height of up to 2m, though the advisory was lifted 90 minutes later and no earthquake generated waves were reported along the east coast of Japan.

There are initial reports of several buildings being destroyed and power outages to over 3.5 million homes. Three fatalities have been attributed to this aftershock. Workers at the damaged Fukushima nuclear power station temporarily evacuated the plant, though quickly resumed efforts to stabilize the reactors damaged from the Mw9.0 earthquake. No new leaks or damage has been reported from any of the nuclear facilities impacted by this latest aftershock.

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