Niigata-Chuetsu Oki, Japan, Earthquake
The Earthquake
On 16 July 2007, a magnitude 6.6 shallow earthquake occurred near the west coast of Honshu Japan. It was followed hours later by a deep magnitude 6.8 event. The first event was caused by deformation associated with the boundary between the Amur Plate and the Okhotsk Plate. The second quake, however, was the result of faulting associated with the subducted Pacific Plate (United States Geological Survey [USGS] 2007). Two days after the initial earthquakes, an aftershock of magnitude 4.0 occurred. More than 70 smaller aftershocks rattled the Niigata Prefecture and its vicinity over the next few days.
Because the seimic waves associated with shallow quakes can reach the surface without much loss of energy, they produce stronger shaking and usually more damage. Figure 1a presents the shakemap intensity for the magnitude 6.6 event as felt according to the Modified Mercalli Intensity (MMI) scale. This quake is classified as a VI to VIII event on the MMI scale. This MMI corresponds to strong shaking and moderately heavy damage. Figure 1b presents the results of the USGS community internet intensity map. The 6.6 event is classified as having an intensity of VIII.
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The Earthquake
On 16 July 2007, a magnitude 6.6 shallow earthquake occurred near the west coast of Honshu Japan. It was followed hours later by a deep magnitude 6.8 event. The first event was caused by deformation associated with the boundary between the Amur Plate and the Okhotsk Plate. The second quake, however, was the result of faulting associated with the subducted Pacific Plate (United States Geological Survey [USGS] 2007). Two days after the initial earthquakes, an aftershock of magnitude 4.0 occurred. More than 70 smaller aftershocks rattled the Niigata Prefecture and its vicinity over the next few days.
Because the seimic waves associated with shallow quakes can reach the surface without much loss of energy, they produce stronger shaking and usually more damage. Figure 1a presents the shakemap intensity for the magnitude 6.6 event as felt according to the Modified Mercalli Intensity (MMI) scale. This quake is classified as a VI to VIII event on the MMI scale. This MMI corresponds to strong shaking and moderately heavy damage. Figure 1b presents the results of the USGS community internet intensity map. The 6.6 event is classified as having an intensity of VIII.
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