Earthquake/Tsunami Watch! Magnitude 7.1 - BANDA SEA

USGS ^ | March 2, 2005 | USGS

[IonImplantGuru]

Highly unlikely 7.1 would generate a tsunami! It's a big deal on land if you're near the epicenter - I can testify, having gone through the '89 Loma Prieta quake, which was comparable in magnitude. However there is not enough crustal movement to create a serious tsunami, though you might get a low scale one - like a foot or 2 high near the epicenter.

In comparison, the 12/26 Sumatran mega-quake was over an order of magnitude larger.

[VeniVidiVici]

Boy, I bet after these past few months the worst thing in the world you can do to an Indonesian right now is to sneak up behind them and holler, "BOO".

[IonImplantGuru]

im a science idiot whats the new madrid fault

In December of 1811, a the largest earthquake ever recorded in American History started. This earthquake, called the New Madrid Earthquake because of its primary location on the New Madrid Fault, near New Madrid, Missouri. From the effects of the 1811-1812 earthquakes, it can be estimated that they had a magnitude of 8.0 or higher on the not yet invented Richter scale. Large areas sank into the earth, new lakes were formed, and the Mississippi River changed its course due to the earthquakes. More info at New Madrid quakes

The quake was felt as far away as Boston, where it caused some church bells to ring!

[Strategerist]

Is that a normal pattern? A Line?

The line stuff is pure worthless nonsense.

You'll notice that between any two points on the globe, there's a line.

[Strategerist]

Not quite.

The magnitude scale (it's technically not the "Richter" scale anymore) is in fact logarithmic, but it's logarithmic for ground motion; an 8 has 10 times the ground motion of a 7, a 9 has 100 times the ground motion of a 7.

HOWEVER, in terms of "power" (energy release) it's THIRTY-TWO times more for each magnitude.

So, the Sumatran quake had over 1,000 times the energy of the 7.1 Banda Sea quake today.

[Strategerist]

Too deep for a tsunami. This was a very deep subduction quake. Really doesn't displace the sea bottom at all, hence no tsunami.

A 7.1 can generate a tsunami if it causes an underwater landslide....3,000 people were killed in New Guinea in 1998 by such a quake (which actually wasn't even underwater) causing an offshore landslide and tsunami. However, such tsunamis aren't "tele-tsunami" (Long range)..they're local.

And very, very few M 7 range quakes, even underwater, cause landslides that cause even local tsunami. One in a hundred, and probably less likely than that.

Have to remember that prior to the Sumatran tsunami there hadn't been a large long-range tsunami anywhere in the world for over 40 years.

Damaging tsunami aren not THAT common. However, that 40 years was an incredible insane fluke, more of a statistical fluke than 4 hurricanes hitting Florida last year. Normally there should be at least 1-2 of those a decade.

[Strategerist]

This is a grim topic, but doesnt the Book of Revlations say something about Quakes, and a "Earth Shakes"? Or is that just me.

There are an average of 18 quakes in the world above Magnitude 7 a year.

In 2005, there have only been two such quakes, including the one today. Hence, as has been typical the last few years, there have been fewer large earthquakes in the world than average.

[Lady Heron]

Oops, what was I thinking. The New Madrid fault is the fault that runs through Missouri, Mississippi, West Tennessee area. It caused the Mississippi River to run backwards the last time it had a major earthquake.

Sorry, lack of sleep....no brain.

[Ernest_at_the_Beach]

That's all I recognize too!

[Ernest_at_the_Beach]

Structures weren't right.

See this for one explanation of how they can be caused:

Formation of a tsunami

[Ernest_at_the_Beach]

The Birth of a Tsunami
The most common causes of tsunamis are underwater earthquakes. To understand underwater earthquakes, you must first understand plate tectonics. The theory of plate tectonics suggests that the lithosphere, or top layer of the Earth, is made up of a series of huge plates. These plates make up the continents and seafloor. They rest on an underlying viscous layer called the asthenosphere.

Think of a pie cut into eight slices. The pie crust would be the lithosphere and the hot, sticky pie filling underneath would be the asthenosphere. On the Earth, these plates are constantly in motion, moving along each other at a speed of 1 to 2 inches (2.5-5 cm) per year. The movement occurs most dramatically along fault lines (where the pie is cut). These motions are capable of producing earthquakes and volcanism, which, when they occur at the bottom of the ocean, are two possible sources of tsunamis.

Formation of a tsunami

When two plates come into contact at a region known as a plate boundary, a heavier plate can slip under a lighter one. This is called subduction. Underwater subduction often leaves enormous "handprints" in the form of deep ocean trenches along the seafloor.

In some cases of subduction, part of the seafloor connected to the lighter plate may "snap up" suddenly due to pressure from the sinking plate. This results in an earthquake. The focus of the earthquake is the point within the Earth where the rupture first occurs, rocks break and the first seismic waves are generated. The epicenter is the point on the seafloor directly above the focus.

When this piece of the plate snaps up and sends tons of rock shooting upward with tremendous force, the energy of that force is transferred to the water. The energy pushes the water upward above normal sea level. This is the birth of a tsunami. The earthquake that generated the December 26, 2004, tsunami in the Indian Ocean was a 9.0 on the Richter scale -- one of the biggest in recorded history.

Tsunamigenic EventsThe natural occurrences capable of causing a tsunami are referred to as tsunamigenic events. In addition to earthquakes and volcanism, there are two less likely tsunamigenic events: submarine landslides and submarines volcanoes. Oftentimes, these events accompany major earthquakes, adding to the overall power of a tsunami or creating additional tsunamis. They work the same as the earthquake in that the extreme upward release of energy from the event affects the overlying water.

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This link will take you to some very good animations, using MacroMedia's Flash :

Page containing following text and Animations of the spread of the wave.

Hitting the Water
Once the water has been pushed upward, gravity acts on it, forcing the energy out horizontally along the surface of the water. It's sort of the same ripple effect you get from throwing a pebble in the water, but in reverse: The energy is generated by a force moving out of rather than into the water. The energy then moves through the depths of the water and away from the initial disturbance.

The tremendous force created by the seismic disturbance generates the tsunami's incredible speed. The actual speed of the tsunami is calculated by measuring the water depth at a point in time when the tsunami passes by. The speed is the square root of the product of acceleration of gravity and the quantity of water depth, or:

t = square root (g x d)
t = tsunami speed in meters per second
g = acceleration of gravity (32 feet/10 meters per second/per second)
d = quantity of water depth

Photo courtesy NOAA
An animation of the 2004 Indian Ocean tsunami

A tsunami's ability to maintain speed is directly influenced by the depth of the water. A tsunami moves faster in deeper water and slower in shallower water. So unlike a normal wave, the driving energy of a tsunami moves through the water as opposed to on top of it. As a result, as a tsunami moves though deep water at hundreds of miles an hour, it is barely noticeable above the waterline. A tsunami is typically no more than 3 feet (1 meter) high until it gets close to shore.

Once a tsunami gets close to shore, it takes its more recognizable and deadly form.

Photo courtesy USGS
Simulation of a theoretical tsunami in the Pacific

Tsunami TypesTsunamis are categorized in one of two ways:

• distant tsunamis
• local tsunamis

This distinction is made based on the time it takes the tsunami to leave the source disturbance and reach land.

A distant tsunami travels more than 600 miles (1,000 km) from the source area before it reaches land. Distant tsunamis are more likely to occur in the Pacific Ocean and are capable of traveling across the entire ocean in less than one day. Since distant tsunamis make such long trips with a relatively constant speed, experts can predict their arrival with a fair degree of accuracy. This makes it easy to warn and evacuate people that could be affected by the wave.

A local tsunami travels toward nearby coastal lands within 60 miles (100 km) of the source. Local tsunamis are usually the result of submarine landslides and typically occur in a bay or harbor. Local tsunamis are particularly dangerous because they can reach land within a matter of minutes. This type of "sneak attack" makes it hard to warn the public about the tsunami's approach.

[Ernest_at_the_Beach]

For the curious:

Characteristics of the Tsunami Phenomena

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Several pages into the document we have text describing calculations with this diagram:

[Ernest_at_the_Beach]

Where did everybody go?

[Drango]

Where did everybody go?

LOL...don't you hate it when you're the last post and everyone thinks you're a thread killer? LOL again.

[onyx]

LOL...don't you hate it when you're the last post and everyone thinks you're a thread killer? LOL again.





I don't mind...lol.

[underwiredsupport]

Actually, I thought your Tsunami graphics were pretty cool...but I was still wiping Diet Coke off my LCD from VeniVidiVici's post...about sneeking up behind an Indonesian, and yelling "boo"....sspppeeewww....LOL!!

[Ernest_at_the_Beach]

Well I was off drawing these color charts...just kidding..well at least getting it together...and was just really disappointed to see that everyone had left me....<P.And where did the guy go who ask?