I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

[mooncliff]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

Ah, yes, if only we had many many small ones... we had one the other day that was like someone drove a car into the building... one big thud and that was it.

Unfortunately, that only released about 1/10,000 of what might be expected. When we really do have a M7.5 in Tokyo, the damage will be enormous. It will not be anything like what happened in March, which in Tokyo was nearly nothing.

The March quake did set off quakes under Tokyo a few minutes later. The entire east half of Honshu is experiencing 4 times the normal quake activity.

[Sharky]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

Ah, yes, if only we had many many small ones...

Here's a graphic from USGS where each dot shows a quake near Tokyo since 1990:

Capture.JPG

Also, from the page you linked to in the OP:

The average number of quakes measured at magnitude 3 or more in the five years preceding the March 11 disaster was about eight a month.

The institute discovered that the number of small-scale plate-boundary quakes that are not felt by people has drastically increased following the March 11 earthquake.

Also, the preliminary observed number of magnitude-3 or larger plate-boundary quakes between March 11 and Aug. 20 rose about fourfold in an area 60 to 70 kilometers below northern Tokyo Bay.

Similarly sized plate-boundary quakes occurring 40 to 55 kilometers below southern Ibaraki Prefecture have increased about 20-fold.

we had one the other day that was like someone drove a car into the building... one big thud and that was it.

According to USGS, it looks like that was a mag 4.8 quake, with an epicenter 130 miles ENE of Tokyo (31 Aug, 13:22 UTC):

http://earthquake.usgs.gov/earthquak...orld_japan.php

[mooncliff]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

I meant this one, basically at the north end of Tokyo Bay, basically directly under Tokyo.

http://tenki.jp/earthquake/detail-7879.html

There are so many it is hard even for people who live here to keep track.

[touchring]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

Here's a graphic from USGS where each dot shows a quake near Tokyo since 1990:

[ATTACH]4048[/ATTACH]

Also, from the page you linked to in the OP:





According to USGS, it looks like that was a mag 4.8 quake, with an epicenter 130 miles ENE of Tokyo (31 Aug, 13:22 UTC):

http://earthquake.usgs.gov/earthquak...orld_japan.php

It says here that a mag 9 releases 480 megaton equivalent of TNT, which is 480,000,000 tons. In comparison, a mag 5 releases only 480 tons. So, a mag 9 releases the energy equivalent to 1,000,000 x mag 5. So it would appear to me that you'd need hell a lot of mag 5 to relieve the stress created by the mag 9.

9.0

480 megatons

2.0 EJ

MW Lisbon earthquake (Portugal), All Saints Day, 1755 MW 2011 Tōhoku earthquake and tsunami

5.0

480 metric tons

2.0 TJ

Lincolnshire earthquake (UK), 2008 MW Ontario-Quebec earthquake (Canada), 2010[16][17]

http://en.wikipedia.org/wiki/Richter_magnitude_scale

[c1ue]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

It says here that a mag 9 releases 480 megaton equivalent of TNT, which is 480,000,000 tons. In comparison, a mag 5 releases only 480 tons. So, a mag 9 releases the energy equivalent to 1,000,000 x mag 5. So it would appear to me that you'd need hell a lot of mag 5 to relieve the stress created by the mag 9.

9.0

480 megatons

2.0 EJ

MW Lisbon earthquake (Portugal), All Saints Day, 1755 MW 2011 Tōhoku earthquake and tsunami

5.0

480 metric tons

2.0 TJ

Lincolnshire earthquake (UK), 2008 MW Ontario-Quebec earthquake (Canada), 2010[16][17]

http://en.wikipedia.org/wiki/Richter_magnitude_scale

This is not consistent. If the Richter scale is log based, then a 9.0 earthquake should be 10 exp 4 stronger than a 5.0 earthquake = 10000 times, not 1,000,000 times.

The other misapprehension is that you're assuming the 'earthquake potential' energy is that of a 9.0 magnitude earthquake.

Where is this written?

If the historical record is any guide, it requires decades to build up enough 'earthquake' potential energy to build towards a really big earthquake.

The theory that one really big earthquake has the potential to unleash other large earthquakes has some logical merit given the assumption of built up stresses.

Conversely the idea that the recent 9.0 magnitude earthquake off Fukushima will then see another 9.0, or 7.5 earthquake only 200 miles away in Tokyo seems far fetched.

This is why I asked for a timeline.

[Sharky]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

This is not consistent. If the Richter scale is log based, then a 9.0 earthquake should be 10 exp 4 stronger than a 5.0 earthquake = 10000 times, not 1,000,000 times.

The Richter scale is logarithmic with respect to amplitude, not energy. A 1-point increase means the maximum amplitude was 10 times higher. However, that requires an energy release that's 32 times higher.

So, a 4-point increase in magnitude, as in touchring's post, would be 32^4 = 1,048,576 times as much energy.

http://www.geo.mtu.edu/UPSeis/intensity.html

[touchring]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

The Richter scale is logarithmic with respect to amplitude, not energy. A 1-point increase means the maximum amplitude was 10 times higher. However, that requires an energy release that's 32 times higher.

So, a 4-point increase in magnitude, as in touchring's post, would be 32^4 = 1,048,576 times as much energy.

http://www.geo.mtu.edu/UPSeis/intensity.html

Thanks Sharky, you saved my day. I only knew 1 megabyte is about 1000 kilobytes.

I believe the Richter scale should be discarded and replaced with a linear scale. Just to show how many people underestimate the power of the March Fukushima earthquake.

[c1ue]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

The Richter scale is logarithmic with respect to amplitude, not energy. A 1-point increase means the maximum amplitude was 10 times higher. However, that requires an energy release that's 32 times higher.

So, a 4-point increase in magnitude, as in touchring's post, would be 32^4 = 1,048,576 times as much energy.

http://www.geo.mtu.edu/UPSeis/intensity.html

Fair enough.

The 'potential energy' from stress buildup is still relevant.

One interesting note is the East Coast of the US: the recent earthquake - despite being very mild by West Coast standards, was literally almost the only one of any such magnitude for over 100 years. There were a series of much stronger earthquakes in the late 1800s, but nothing since.

If anything, the 'bad' earthquake is most likely to happen there. We've seen the western Pacific, we've seen Alaska/northern Pacific, we've seen the southern Pacific (New Zealand), and we've seen the eastern Pacific (Chile) cycle twice in the same period.

[touchring]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

Fair enough.

The 'potential energy' from stress buildup is still relevant.

One interesting note is the East Coast of the US: the recent earthquake - despite being very mild by West Coast standards, was literally almost the only one of any such magnitude for over 100 years. There were a series of much stronger earthquakes in the late 1800s, but nothing since.

If anything, the 'bad' earthquake is most likely to happen there. We've seen the western Pacific, we've seen Alaska/northern Pacific, we've seen the southern Pacific (New Zealand), and we've seen the eastern Pacific (Chile) cycle twice in the same period.

There had been numerous record breaking quakes in the recent 10 years.

The Sichuan earthquake destroyed temples that were over 2000 years old.

The ErWang Temple built around 250BC survived 2260 years only to be destroyed in the 2008.

Tokyo, formerly Edo was founded during the Tokugawa in late 1500s, why was that area largely uninhabited before that? The West coast of America had only been inhabited by civilization for less than 300 years. We never know if a 50 foot tsunami had slammed into BC and the state of washington 800 years ago.

The March 2011 Tohoku Earthquake is also a record breaker. A Mag 9 earthquake had never been recorded in Japan - http://en.wikipedia.org/wiki/List_of...uakes_in_Japan

We are in uncharted waters...

Before:



After:



More:
http://cristyli.blogspot.com/2008/06...treasures.html

[c1ue]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

The Sichuan earthquake destroyed temples that were over 2000 years old.

So? Earthquakes even in the same area only destroy buildings if they are very strong and close.

Tokyo, formerly Edo was founded during the Tokugawa in late 1500s, why was that area largely uninhabited before that?

Your history again shows its lack. The Tokyo area was inhabited continuously as long as most of Japan. It was just that there was no benefit to taking advantage of Tokyo's gigantic natural harbor given Japan's relations with its neighbors until relatively recently.

The West coast of America had only been inhabited by civilization for less than 300 years. We never know if a 50 foot tsunami had slammed into BC and the state of washington 800 years ago.

The West coast of America was sparsely inhabited because it was a really crappy place to live.

Without irrigation, most of the areas of California which are densely populated today was and would return to being desert.

As for tsunamis, no matter how big a tsunami was, it would not have affected anyone living more than 10 miles inland.

Your attribution of the low population density to tsunamis is ridiculous.

[jpatter666]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

As for tsunamis, no matter how big a tsunami was, it would not have affected anyone living more than 10 miles inland.

Your attribution of the low population density to tsunamis is ridiculous.

Was curious about the tsunami thing and looked up the following: http://wiki.answers.com/Q/How_far_in...n_a_tsunami_go

Don't think touchring was saying the population density was related to tsunamis, just that we lack detailed historical data on their prevalence in that region -- at least that's how I read it.

[touchring]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

Was curious about the tsunami thing and looked up the following: http://wiki.answers.com/Q/How_far_in...n_a_tsunami_go

Don't think touchring was saying the population density was related to tsunamis, just that we lack detailed historical data on their prevalence in that region -- at least that's how I read it.

The recent tsunami in Japan went over break waters 30 feet in height. It is not so much of distance but rather height above sea level. Properties more than 40 feet above sea level (high tide) should be safe. 50 feet to be really safe...

http://youtu.be/uuBi7vRCsLM

[Sharky]

Re: I think we are about to have one or two Magnitude 7.5 quakes directly under Tokyo

The recent tsunami in Japan went over break waters 30 feet in height. It is not so much of distance but rather height above sea level. Properties more than 40 feet above sea level (high tide) should be safe. 50 feet to be really safe...

Unless you're worried about the Hilina Slump in Hawaii or the La Palma island risk in the Atlantic, in which case you might want to aim for something a little higher.

http://en.wikipedia.org/wiki/Hilina_Slump
http://en.wikipedia.org/wiki/La_Palma#Tsunami_scenarios