Powerful Earthquake Strikes Honshu, Japan

Japan Quake Update [June 18, 2008]

• Death toll: At least 10 people
• Missing: 12 people
• Injured: About 250 people
• Evacuees: About 300 people spent Saturday night in evacuation centers

Recent quake history:

• October 2004. A magnitude 6.8 earthquake struck Niigata prefecture in northern Japan, killing 65 people and injuring about 3,500 others.
• January 1995. A Mw 6.8 [the Moment magnitude scale, USGS,] struck the city of Kobe in 1995, killing 6,434 people, many were injured and up to 500,000 people lost their homes.
• September 1923. The worst earthquake in Japan, the Great Kantō earthquake, estimated to have had a magnitude between 7.9 and 8.4, claimed up to 142,000 lives. The biggest cause of death was the fires which spread rapidly due to high winds from a typhoon. In the worst single incident, up to 40,000 people who had fled their homes and businesses gathering in an Army Parade Ground in central Tokyo were incinerated by a firestorm. Tokyo, the port of Yokohama, neighboring prefectures of Chiba, Kanagawa, and Shizuoka were devastated by the quake. the quake caused the equivalent of about $200 billion in damage, more than 2.5% of Japan’s GDP that year.

6.8Mw Quake Occurred Near Akita, Japan

A Magnitude 6.8 Earthquake struck Japan’s Iwate prefecture, east of the main island of Honshu Saturday, June 14, 2008 at 08:43:46 AM local time. At least six people have been killed with 8 others missing and more than 200 injured.

The mainshock was followed by a cluster of aftershocks including at least 12 strong aftershocks measuring between 4.5 to 5.5Mw as of 07:11:57 PM (time at epicenter.)

A highway bridge lies in ruins in Ichinoseki city, Iwate Prefecture, June 14, 2008. A powerful earthquake rocked rural northern Japan on Saturday sparking huge landslides that blocked roads and isolated residents. REUTERS/KYODO. Image may be subject to copyright. See FEWW Fair Use Notice!

The following details were reported by USGS:

• Magnitude: 6.8
• Date-Time: Friday, June 13, 2008 at 23:43:46 UTC
  Saturday, June 14, 2008 at 08:43:46 AM at epicenter
• Location: 39.103°N, 140.668°E
• Depth: 10 km
• Region: EASTERN HONSHU, JAPAN
• Distances: 80 km SSW of Morioka, Honshu, Japan
  85 km SE of Akita, Honshu, Japan
  95 km N of Sendai, Honshu, Japan
  390 km NNE of TOKYO, Japan

Image: USGS

Map of Japan. Source: USGS

The local news sources in Japan have reported the quake as 7.2 magnitude [presumably using the old, or the revised JMA magnitude scale.]

Tectonic Summary
The Mw 6.8 Honshu earthquake of June 13th 2008 occurred in a region of convergence between the Pacific Plate and the Okhotsk section of the North American Plate in northern Japan, where the Pacific plate is moving west-northwest with respect to North America at a rate of approximately 8.3 cm/yr. The hypocenter of the earthquake indicates shallow thrusting motion in the upper (Okhotsk) plate, above the subducting Pacific plate, which lies at approximately 80 km depth at this location.

The earthquake occurred in a region of upper-plate contraction, probably within the complicated tectonics of the Ou Backbone Range, known to have hosted several large earthquakes in historic times. The largest of these events occurred in 1896, approximately 70km north of the June 13th event, and killed over 200 people in the local area. [Source: USGS]