Very strong aftershocks (seashocks) in the northern part of Honshu, Japan

Last update: April 21, 2011 at 3:40 am by By

UPDATE 3:31 UTC : JMA has not listed the current aftershocks. Other international seismological services (USGS, EMSC) are picking up the signals though.

UPDATE 3:18 UTC : As the current aftershocks are coming near to Hokkaido, here are some historical earthquakes which have struck Hokkaido in the past : The region has been rocked by an catastrophic earthquake/tsunami of Magnitude 9 in 1667 A.D., a magnitude 8.2 in 1952, a 1968 quake measuring 8.3 Mw, and one in 2008 measuring 7.1, all bearing the name Tokachi-Oki and a 1973 quake to the immediate north along the Kuril Trench plate boundary, called the 1973 Nemuro-Oki Earthquake.

UPDATE 3:10 UTC : Historical seismicity shows 2 massive shallow earthquakes to the north of the current epicenter

UPDATE 2:58 UTC : We fear that a new section of the subduction zone is becoming unstable with the risk of many aftershocks

UPDATE 2:55 UTC : The epicenter lies along the same subduction zone responsible for the massive March 11 earthquake.

April 21 2011 earthquake (aftershocks) hazard map

UPDATE 2:52 UTC : The epicenter of the aftershocks is coming a lot closer to Hokkaido

UPDATE 2:50 UTC : Maximum intensity for both aftershocks = 3 (on a scale from 0 to 7).

2 very strong aftershocks on top of the subduction zone of northern Honshu but luckily at a safe distance out of the coast. The location of the epicenter is surprisingly more to the north of 90% of the other aftershocks.
Epicenter is at least 150 km from the coastline and this NOT dangerous.
There was NEVER a tsunami danger.

Most important Earthquake Data:
Magnitude : 6.0
UTC Time : Thursday, April 21, 2011 at 01:54:40 UTC
Local time at epicenter : Thursday, April 21, 2011 at 11:54:40 AM at epicenter
Depth (Hypocenter) : 3.7 km
Geo-location(s) :
187 km (116 miles) E of Hachinohe, Honshu, Japan
226 km (140 miles) ENE of Morioka, Honshu, Japan

Links to important maps
USGS Did You Feel It Map
Google satellite map of the area showing the kind of terrain the earthquake took place
USGS historic earthquakes map
USGS Seismic hazard map
USGS Impact on Population map
USGS Shaking map
LIVE SEISMOGRAM (nearest Seismograph station)
GDACS GREEN earthquake report

Data of aftershock 1
M 5.8      2011/04/21 00:39     Depth 15.0 km      OFF THE EAST COAST OF HONSHU, JAPAN
10:39:04 AM at epicenter
Very strong aftershock on top of the subduction zone of northern Honshu but luckily at a safe distance out of the coast.
169 km (105 miles) E of Hachinohe, Honshu, Japan
217 km (134 miles) ENE of Morioka, Honshu, Japan
Satellite map of the greater epicenter area

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