7.3 Magnitude Quake Hits North Japan

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Discussion Overview

The discussion centers around a recent 7.3 magnitude earthquake that struck northern Japan, including details about its depth, potential tsunami implications, and comparisons to previous seismic events. The scope includes technical aspects of earthquake measurement, tsunami warnings, and geological context.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • Some participants express concern about the earthquake's impact, noting that a tsunami advisory was issued for Fukushima and Miyagi prefectures, with expected wave heights of up to 1 meter above normal tidal levels.
  • Details of the earthquake's epicenter and depth are provided, with a preliminary depth of 60 kilometers and a preceding 6.4 magnitude quake occurring shortly before.
  • One participant suggests that the depth of the earthquakes may mitigate tsunami risk, depending on the displacement of the ocean floor and water volume.
  • Another participant questions whether the recent earthquakes are aftershocks of the 2011 Great Tohoku earthquake, while also suggesting they may be part of ongoing seismic activity related to tectonic plate interactions.
  • Comparisons are made to the 2011 earthquake, highlighting differences in depth and potential implications for tsunami generation.

Areas of Agreement / Disagreement

Participants express varying views on the nature of the recent earthquakes, with some suggesting they are aftershocks while others argue they are part of ongoing seismic activity. There is no consensus on the implications for tsunami risk or the relationship to past seismic events.

Contextual Notes

Participants reference specific depths and magnitudes of earthquakes without resolving the implications of these factors on tsunami generation or seismic activity. The discussion includes links to external sources for further information.

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TL;DR
7.3 Magnitude Quake Hits North Japan, Tsunami Alert Issued
3-16-2022_quake.JPG
https://www.bloomberg.com/news/arti...e-quake-hits-north-japan-tsunami-alert-issued
 
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Yikes. That's not good...

Although, if it really is only 1 meter above normal tidal levels, that's a lot less than the previous one, right?

https://www.cnn.com/2022/03/16/asia/japan-earthquake-fukushima-intl/index.html

The tsunami advisory was made for Fukushima and Miyagi prefectures in eastern Japan following the quake that had a preliminary epicenter depth of 60 kilometers (37 miles), according to the Japan Meteorological Agency.

The advisory warns of tsunami heights reaching up to 1 meter above normal tidal levels, with the initial waves reaching shore around midnight local time (11 a.m. ET).
 

M 7.3 - 57 km ENE of Namie, Japan​

https://earthquake.usgs.gov/earthquakes/eventpage/us6000h519/executive
  • 2022-03-16 14:36:33 (UTC)
  • 37.702°N 141.587°E
  • 63.1 km depth
The Mag 7.3 was preceded by a Mag 6.4 earthquake occurring only 2 minutes before and slightly shallower.

M 6.4 - 62 km ENE of Namie, Japan​

https://earthquake.usgs.gov/earthquakes/eventpage/us6000h518/executive
  • 2022-03-16 14:34:27 (UTC)
  • 37.633°N 141.685°E
  • 56.3 km depth
An aftershock

M 5.5 - 77 km SE of Ishinomaki, Japan​

https://earthquake.usgs.gov/earthquakes/eventpage/us6000h518/executive
  • 2022-03-16 15:52:31 (UTC)
  • 37.853°N 141.827°E
  • 67.2 km depth (slightly deeper than the Mag 7.3)
 
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Those earthquakes are very deep.
Maybe they are aftershocks of the big tsunami earthquake.
 
Baluncore said:
Those earthquakes are very deep.
Maybe they are aftershocks of the big tsunami earthquake.
I would consider that a moderate depth, but perhaps enough to mitigate a tsunami. Of course, it all depends on how and how much of the ocean floor and volume of ocean water is displaced.

In contrast, the 9.1/9.2 Mag Great Tohoku earthquake of 2011 was at a depth of 29 km.
https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/executive

M 9.1 - 2011 Great Tohoku Earthquake, Japan​

  • 2011-03-11 05:46:24 (UTC)
  • 38.297°N 142.373°E
  • 29.0 km depth
Rather than aftershocks, the current quakes are simply part of the ongoing seismic activity induced by the flow of the seafloor under crust of which Japan is a part, i.e., subduction of the western edge of the Pacific Plate under the Okhotsk Plate.
https://en.wikipedia.org/wiki/Japan_Trench#Seismicity
https://en.wikipedia.org/wiki/Okhotsk_Plate
https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/dyfi/intensity
 

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