Just a couple of questions …

Japan 2011

From http://www.livescience.com/39110-japan-2011-earthquake-tsunami-facts.html

_…there had been hints of the disaster to come. The areas flooded in 2011 closely matched those of a tsunami that hit Sendai in 869. In the decade before the 2011 Tohoku earthquake, a handful of Japanese geologists had begun to recognize that a large earthquake and tsunami had struck the northern Honshu region in 869.___

How did the geologists figure this out?

From BOM’s FB page

A magnitude 7.6 earthquake near the South Island of New Zealand on 17 June 1929 generated a tsunami which measured 0.2 metres at Fort Denison in Sydney Harbour.

Fort Denison is this little island

What would it have done? Would the water levels have dropped in the harbour beforehand? What would it have looked like?

How did the geologists figure this out?

debris beds?

JudgeMental said:

How did the geologists figure this out?

debris beds?

Could be. But how did they pinpoint the year? Were there accurate written records by then?

Pethaps the debris beds laid in wait of recognition?

http://historyofgeology.fieldofscience.com/2011/03/historic-tsunamis-in-japan.html

Recognized Tsunamis sediments in Japan go back nearly for 5.000 years, historic records span for nearly 1.300 years, however the most detailed and precise accounts cover mostly the recent period.

An earthquake offshore the north-eastern coast generated a large-scale tsunami on July 13. in 869, we read in the Nihon Sandai Jitsuroku – the “The True History of Three Reigns of Japan” compiled in the year 901.

more at link and more links.

The word is Japanese. The Japanese first observed and named the phenomenemon.

roughbarked said:

The word is Japanese. The Japanese first observed and named the phenomenemon.

enemeomnomenen…

Speedy said:

JudgeMental said:

How did the geologists figure this out?

debris beds?

Could be. But how did they pinpoint the year? Were there accurate written records by then?

Tram or Bus tickets?

Watching Blood and thunder then sitting back. I wrote a couple of new riffs just then.

JudgeMental said:

http://historyofgeology.fieldofscience.com/2011/03/historic-tsunamis-in-japan.html

Recognized Tsunamis sediments in Japan go back nearly for 5.000 years, historic records span for nearly 1.300 years, however the most detailed and precise accounts cover mostly the recent period.

An earthquake offshore the north-eastern coast generated a large-scale tsunami on July 13. in 869, we read in the Nihon Sandai Jitsuroku – the “The True History of Three Reigns of Japan” compiled in the year 901.

more at link and more links.

That is an interesting read.

I’ve never heard the term “orphan tsunami” before. It’s when an earthquake is not felt beforehand (and there are some tsunamis which are followed by an earthquake).

It also stated that some tsunamis are preceded by a loud sound like thunder. What’s that all about?

roughbarked said:

roughbarked said:

The word is Japanese. The Japanese first observed and named the phenomenemon.

enemeomnomenen…

Speedy said:

It also stated that some tsunamis are preceded by a loud sound like thunder. What’s that all about?

The only earthquake I ever noticed that sounded like thunder turned out to be directly under me.

Not that I’ve noticed many. Mostly it would be a shimmer of the horizon.

Speedy said:

roughbarked said:

roughbarked said:

The word is Japanese. The Japanese first observed and named the phenomenemon.

enemeomnomenen…

Thanks ;)

roughbarked said:

Speedy said:

It also stated that some tsunamis are preceded by a loud sound like thunder. What’s that all about?

The only earthquake I ever noticed that sounded like thunder turned out to be directly under me.

Not that I’ve noticed many. Mostly it would be a shimmer of the horizon.

The article listed it as a warning signal, along with the sea levels receding.

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

Speedy said:

roughbarked said:

Speedy said:

It also stated that some tsunamis are preceded by a loud sound like thunder. What’s that all about?

The only earthquake I ever noticed that sounded like thunder turned out to be directly under me.

Not that I’ve noticed many. Mostly it would be a shimmer of the horizon.

The article listed it as a warning signal, along with the sea levels receding.

In the case of Japan, have you looked at all the shocks they get? In my case I’m talking of only one shock Ive stood upon and the best science I could get out of a scientist was that maybe we, the seven of us who noted it, were standing directly above it and that it was a 1 on the scale that was quite close to the surface.

The seven of us were awake at 2:10 AM along a line that stretched over about 20 km.

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

Yeah but, tsunami will depend on where it happens mostly because this is a different type of fault.

roughbarked said:

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

Yeah but, tsunami will depend on where it happens mostly because this is a different type of fault.

In places the San Andreas fault goes under the harbour.

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

As an area of stock standard dirt, 200 m * 200 m * 200 m will mass very approximately 10 billion tonnes I expect that you’re probably a tad shy on your estimate of the amount of mass that will actually move :)

roughbarked said:

The seven of us were awake at 2:10 AM along a line that stretched over about 20 km.

I have felt 2 earthquakes. One was the Newcastle one. I was standing on an indoor staircase talking to some people downstairs in the kitchen. We all heard the sliding glass panels in one of the kitchen cabinets rattling loudly and were stunned into silence. Within about 5 minutes it was all over the news on TV.

The second was about 5 years ago near Canberra. We were staying with some relos and in the middle of the night I felt a shudder. It woke me up. It wasn’t until morning that I realised that a few others in the house had felt it too. Not sure whether, when you’re asleep, you can differentiate between sound and movement/shuddering. Perhaps this is what you “heard”?

AwesomeO said:

roughbarked said:

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

Yeah but, tsunami will depend on where it happens mostly because this is a different type of fault.

In places the San Andreas fault goes under the harbour.

It still slides along rather than slide over and drop off.

sibeen said:

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

As an area of stock standard dirt, 200 m * 200 m * 200 m will mass very approximately 10 billion tonnes I expect that you’re probably a tad shy on your estimate of the amount of mass that will actually move :)

Maybe an AwsomeO “few” is almost infinite.

The Rev Dodgson said:

sibeen said:

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

As an area of stock standard dirt, 200 m * 200 m * 200 m will mass very approximately 10 billion tonnes I expect that you’re probably a tad shy on your estimate of the amount of mass that will actually move :)

Maybe an AwsomeO “few” is almost infinite.

You could have something there.

The Rev Dodgson said:

sibeen said:

AwesomeO said:

I was reading something a while ago, the San Andreas fault complex, I say complex because it is mapped pretty accurately and it is not just one line, but anyhoo, at two inches or so a year, there are now two plates that are 14 feet out of position and held back by the friction of interlocking rocks and whatever. When that lot let go and a few billion tons of dirt move 14 feet that is gonna cause one hell of a mess.

As an area of stock standard dirt, 200 m * 200 m * 200 m will mass very approximately 10 billion tonnes I expect that you’re probably a tad shy on your estimate of the amount of mass that will actually move :)

Maybe an AwsomeO “few” is almost infinite.

I should have just said shed load.

> A magnitude 7.6 earthquake near the South Island of New Zealand on 17 June 1929 generated a tsunami which measured 0.2 metres at Fort Denison in Sydney Harbour.

Yep. The Gold and Sunshine coasts are at higher risk because of the possibility of earthquakes and landslides on the seismically active ridge north of New Zealand. Broome is far from safe. The great barrier reef would help to protect north Qld, and there isn’t much out to sea from Victoria, SA and Perth that could cause a tsunami.

Whether the water recedes first or piles up first depends on the direction in which the earthquake slips. It has a 50-50 chance of being either.

mollwollfumble said:

Whether the water recedes first or piles up first depends on the direction in which the earthquake slips. It has a 50-50 chance of being either.

Thanks moll.