Magnitude 7.1 - NEAR THE EAST COAST OF HONSHU, JAPAN

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2011 April 07 14:32:41 UTC

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Earthquake Details

  • This event has been reviewed by a seismologist.
Magnitude7.1
Date-Time
Location38.253°N, 141.640°E
Depth49 km (30.4 miles)
RegionNEAR THE EAST COAST OF HONSHU, JAPAN
Distances66 km (41 miles) E of Sendai, Honshu, Japan
114 km (70 miles) E of Yamagata, Honshu, Japan
116 km (72 miles) ENE of Fukushima, Honshu, Japan
330 km (205 miles) NNE of TOKYO, Japan
Location Uncertaintyhorizontal +/- 13.1 km (8.1 miles); depth +/- 7.2 km (4.5 miles)
ParametersNST=426, Nph=427, Dmin=358.4 km, Rmss=0.75 sec, Gp= 32°,
M-type=regional moment magnitude (Mw), Version=B
Source
  • USGS NEIC (WDCS-D)
Event IDusc0002ksa
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Earthquake Summary

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Felt Reports

Two people killed, 132 injured and several roads damaged in the Ishinomaki-Onagawa area. One person died in Yamagata when a power outage interrupted oxygen supply. Felt (VII) at Sendai, (V) at Misawa and (IV) in the Tokyo-Yokohama area. Felt (V) at Sapporo, Hokkaido. Felt widely in central and northern Honshu and in southern Hokkaido. Recorded (6U JMA) in Miyagi.

Tectonic Summary

The April 7, 2011 earthquake near the east coast of Honshu, Japan occurred as a result of thrust/reverse faulting on or near the subduction zone plate boundary between the Pacific and North America plates. At the latitude of this earthquake, the Pacific plate moves approximately westwards with respect to the North America plate at a rate of 83 mm/yr, and begins its westward descent beneath Japan at the Japan Trench. Note that some authors divide this region into several microplates that together define the relative motions between the larger Pacific, North America and Eurasia plates; these include the Okhotsk and Amur microplates that are respectively part of North America and Eurasia.

The epicenter and focal-depth of the April 7 earthquake are consistent with the event having occurred very close to the main interface thrust-fault of the subduction zone plate boundary. Preliminary focal-mechanisms, however, imply slip on a fault with steeper dip than that of the main interface thrust-fault, which may imply an intraplate source is more likely.

This earthquake can be considered an aftershock of the March 11, 2011 Mw 9.0 Tohoku earthquake. The aftershock sequence of that event has been ongoing since March 11, and has included 58 earthquakes of M 6 or greater up until April 7 2011, two of which were greater than M 7 (M7.7 and M7.9, both on March 11). Over the two days preceding the March 11 earthquake, a series of large foreshocks had occurred, beginning on March 9th with a M 7.2 event approximately 40 km from the epicenter of the March 11 earthquake, and continuing with another three earthquakes greater than M 6 on the same day. Prior to March 9 2011, the Japan Trench subduction zone had hosted nine events of magnitude 7 or greater since 1973. See the tectonic summary of the March 11 event for more details of the historic seismicity in this region.

Earthquake Information for Asia

Earthquake Information for Japan