AIR’s Initial Analysis of Japanese Quake

June 17, 2008

Boston-based AIR Worldwide has issued a bulletin on the earthquake that struck northern Japan on Saturday, June 14 (See IJ web site – The quake struck in a sparsely populated region, about 390 kilometers (243 miles) north of Tokyo.

AIR estimated “that total insurable property value within the affected area—which spans four prefectures—is about JPY 3.8 trillion [$351 billion]. However, it should be noted that take-up rates (the percentage of properties that actually carry earthquake insurance) are relatively low.”

While first reports put the earthquake at magnitude 7.2, AIR said that both the “USGS and the Japan Meteorological Agency (JMA) have reported a moment magnitude of between 6.8 and 6.9 for the event. Depth was estimated at 10 kilometers [6 miles].”

“The earthquake occurred in a region of northern Japan where the Pacific Plate and the Okhotsk section of the North American Plate converge,” explained Mehrdad Mahdyiar, director of earthquake hazard at AIR Worldwide. “The Pacific plate moves west-northwest with respect to North America at a rate of 8.3 cm/yr [approx. 5 inches]. This is a region of upper-plate contraction. More than likely, it is also located within the complicated tectonics of the Ou Backbone Range, the site of several large earthquakes throughout recorded history, the largest of which occurred in 1896. That quake struck some 70km north of Saturday’s event and killed more than 200 people.”

He added that the “focal mechanism indicates that the current event was a shallow thrust earthquake. It may have ruptured an active fault called the Detana Fault. Within a 100km [60 mile] radius, 15 earthquakes exceeding M6.0 have occurred since 1800; since 1900, there have been 56 exceeding M5.0.”

AIR also noted that more than 470 aftershocks have occurred since the main quake, “making it difficult for rescue workers to access roads and search for survivors. About 3,500 homes remain without water and some 3,000 households have no electricity. A semiconductor plant in Iwate prefecture suspended production for 2 or 3 days. Elsewhere, in nearby Fukushima prefecture, the earthquake spilled radiation contaminated water from a collecting pool owned by Tokyo Electric Power Co, Asia’s biggest power utility.”

AIR also pointed out that Japan’s strict building codes – and their enforcement – prevented the quake from becoming a major disaster, as “most modern buildings remained intact, in large part due to the country’s strict construction codes.”

According to the most recent information from Japan’s Fire Disaster Management Agency (FDMA),” four structures collapsed and 6 others were severely damaged. In the current report, about 200 structures sustained some degree of damage from this event.”

Source: AIR Worldwide –

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