Scientists study May's Tonga earthquake (8.0 Mag and no tsunami)

UPI ^ | March 12, 2007

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Published: March 12, 2007 at 8:39 AM

Scientists study May's Tonga earthquake

ST. LOUIS, March 12 (UPI) -- A U.S.-led team of seismologists says it has determined why last May's major earthquake in Tonga did not cause a large tsunami.

Professor Douglas Wiens at Washington University in St. Louis and colleagues in Australia, Japan and Tonga said although a Pacific Rim tsunami warning was issued following the May 3, 2006, magnitude 8.0 quake, the resulting tsunami was very minor and caused no damage.

Tsunamis generally result from shallow-thrust earthquakes, which occur when the seafloor is pushed downward beneath the land in places like Japan, Chile, Indonesia and Mexico. The researchers found the May earthquake was, instead, a slab-tearing event that ruptured the down-going seafloor beneath Tonga.

That, said the scientists, explains why the tsunami was smaller than expected, and suggests large earthquakes in Tonga may typically be of the slab-tearing variety, consistent with the lack of large historical tsunamis in Tonga.

Wiens and graduate student David Heeszel presented the study in December during the winter meeting of the American Geophysical Union in San Francisco.

[bd476]

Updated: 7.9 Earthquake Tonga (Northeast of Australia)

8.1 Earthquake in TONGA

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Scientists discover how an 8.0 Earthquake did not cause a tsunami.

Earthquake Ping List. Please send a Freepmail if you want to be added or removed from this list.

[bd476]

Now they are saying that there was no tsunami generated after the 8.0 quake in Tonga last May. However, at the time, Reuters did report a small tsuami.

At least the UPI article discusses briefly the mechanics of a tsunami.

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Tsunamis can also be generated by local quakes such as the Papua New Guinea Tsunami in 1998 which struck after a 7.0 earthquake. The New Guinea Tsunami claimed approximately 3000 lives.

Tsunamis are characterized as shallow water waves. Most distance travelling tsunamis break out in the ocean rather than at a shoreline. Damage from most tsunamis is from water swelling up, inundating and washing over the coast line.

• "On July 17, 1998 a Mw = 7.0 earthquake struck the north central coast of Papua New Guinea. Following the earthquake a large tsunami also struck the region. Initial reports claimed that the wave was between 7 and 10 meters and that up to 3000 persons were killed or missing. This seemed to be an unusually damaging tsunami given the size of the earthquake..."

• "Tsunamis are a series of very long waves generated by any rapid, large-scale disturbance of the sea. Most are generated by sea floor displacements from large undersea earthquakes."

• "Tsunamis can cause great destruction and loss of life within minutes on shores near their source, and some tsunamis can cause destruction within hours across an entire ocean basin. Most tsunamis occur in the Pacific region but they are known to happen in every ocean and sea..."
  NOAA Tsunami

• "A tsunami can be generated by ANY disturbance that displaces a large water mass from its equilibrium position. Submarine landslides, which often occur during a large earthquake, can also create a tsunami."
  Tsunami Generation, Propagation, and Inundation

• "What causes a tsunami? "

• "Oceanographers often refer to tsunamis as seismic sea waves as they are usually the result of a sudden rise or fall of a section of the earth's crust under or near the ocean.

• A seismic disturbance can displace the water column, creating a rise or fall in the level of the ocean above. This rise or fall in sea level is the initial formation of a tsunami wave..."

• "...Tsunami waves can also be created by volcanic activity and landslides occurring above or below the sea surface. These types of activity produce tsunamis with much less energy than those produced by submarine faulting.

  The size and energy of these tsunamis dissipates rapidly with increasing distance from the source, thus resulting in more local devastation..."
  Tsunami.org

[dr_lew]

Reminds me of the caption to an absurdly complicated weather map in Tom Weller's Science Made Stupid, "Looks like rain mebbe ... or mebbe not."

[gr8eman]

Of course it was caused by global warming...if you drive your SUV to work everyday Tonga will get wiped out on May 23, 2205.

[dr_lew]

To be fair, the global warming connection to tsunamis is supposed to be that rising sea levels make places like Tonga more SUSCEPTIBLE to tsunamis, not that global warming CAUSES tsunamis. 'Course, the global warmists play it both ways too, so what the heck!

[gr8eman]

that's right...I forgot...the sea level will rise 25.07 feet by 2235. Sorry!

[Global2010]

Thanks for posting tsunami info.


I stand corrected from the other day I had posted quite a bit of small seismic activity in N.Cali and you wrote back yes and Central Cali. Heh that is what I meant to say Central Cali. Thanks for your tactful correction.

Gulf of Cali has been active this last month or so to more than usual lately but after all this time I didn't expect a 6.o to hit.

Ya just never know.

That was fun seeing the Ohio freepers perk up.....all the joking and ribbing we get when we feel one little one from the non earthquake areas and then.....

I got a kick out of that.

[Global2010]

Yeah, well to capture an audience in another decade they will call it Global Cooling.

Some legit scientists came out and wrote the polar bears will adapt.

My thought on everything as the world climate goes through its perpetual change.

[Experiment 6-2-6]

Hm, my beach house faces South to Tonga, and I don't recall seeing a tsunami...

The windows did rattle that morning, however..