Mw 7.0 Earthquake strikes Japan in the same region

Mw 7.0 Earthquake strikes Japan in the same region

  • Earth In The News
16 Apr 2016

Less than 48 hours after Japan was struck by a magnitude-6.2 earthquake, or M6.5 according to the Japan Meteorological Agency (JMA), a second event of Mw 7.0 (M7.3) occurred in the same region on 16 April 2016.  

This is Japan’s largest inland earthquake since the Mw 6.9 (Mj 7.3) Great Hanshin earthquake (also known as the Kobe earthquake) in 1995, and the Mw 6.9 (Mj 7.2) Iwate earthquake in 2008. 

Because the earthquake on 14 April 2016 is smaller in magnitude, that earlier earthquake is now considered to be a foreshock to today’s mainshock. Preliminary data show that the epicentres of both earthquakes are located in close proximity to each other. Their aftershock sequences are closely aligned to the Futugawa-Hinagu fault system, indicating that it is likely that the Futugawa fault is the source of the Mw 7.0 earthquake. 

Scientists from the Earth Observatory of Singapore (EOS) have noted that both earthquakes’ aftershock distribution patterns are similar to each other, although the aftershocks from the Mw 7.0 event appear to extend further along the active Futagawa fault towards Mount Aso, Japan’s largest active volcano. Researchers in Japan are now closely monitoring the activity of Mount Aso to see if this morning’s earthquake would trigger its volcanic activities further.

Based on early information obtained from the United States Geological Survey, Japan’s National Research Institute for Earth Science and Disaster Prevention, and JMA, EOS scientists believe that the earlier rupture at the Mifune fault triggered today’s rupture at the Futagawa fault. The findings from geological investigations indicate that the Futugawa fault has not undergone a rupture for thousands of years. 

According to EOS Research Fellow Dr Wang Yu, Japanese researchers had for some time identified the Futugawa fault as one of the top 20 faults likely to rupture within the next 30 years, based on the average recurrence interval of 3,100 years and that the last major earthquake event at the Futugawa fault occurred many thousands of years ago.

Using data from seismometers around the world, it has been determined that both the Mifune and Futugawa ruptures occurred close to the earth surface. Japanese geologists are already on their way to ascertain if the ruptures have in fact broken to the surface.  If indeed they have, extensive damage to buildings and other infrastructure along the active fault can be expected.

The aftershock distributions after the Mw 6.5 foreshock on 14 April 2016 (yellow) and the Mw 7.3 mainshock (blue). (Data source: Active Fault Database of Japan & NIED Automatic Earthquake Catalog)

Cover image credit: US Geological Survey

Related news: Mw 6.2 Earthquake Strikes Japan

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