Vocal Voices

The past few weeks have seen a number of large earthquakes in the Pacific.

For every one the US Geological Survey has issued tsunami warnings. With a few localised exceptions these tsunamis have been minor, some of them only a few cm above normal sea levels. Yes they are long frequency waves that keep on coming and they have normal waves on them, but they also need height to cause most damage.

The problem for the USGS is that it does not seem to have the ability at the moment to adequately define what type and strength of tsunami is on the move. It issues a tsunami warning and those in its path evacuate or move to higher ground only for there to be little or no disruption. If this carries on then one day there will be another like the one in Thailand and nobody will take notice - disaster!

What the USGS urgently needs is a way to classify tsunamis in the way we do with typhoons and tornadoes.

Hard to do though. It depends if it sets off an underwater landslide or not. That's what did for the Indonesian one.

Suff wrote:Hard to do though. It depends if it sets off an underwater landslide or not. That's what did for the Indonesian one.

Totally agree.

It is why those countries in the known danger zones, and not just the US, are probably going to have to invest in some new form of measuring a tsunami's features over and above of the present sonardyne systems to cut out the guesswork and false alarms. Maybe some sort of satellite array could be employed.

Suff wrote:Hard to do though. It depends if it sets off an underwater landslide or not. That's what did for the Indonesian one.

Suff has nailed the problem, really, and I can't see a solution myself - any given earthquake of any given magnitude may or may not trigger an underwater landslide purely on localised topography which may or may not cause a tsunami.

One of the problems with earth tremors is the fault line system in the locality can produce very varied effects. The Dudley earthquake (4.something from memory) is a case in point. My S. lives about 5 miles south-west from epicentre and felt absolutely nothing. We lived 15 miles from the epicentre, and it jolted me awake and sent me to look out of the window wondering what had happened. 5 miles further away in Tamworth, the Dad of someone I worked with, who was a security guard doing his rounds, was actually thrown to the ground. The thing was, there was a series of faults that got "twanged" by the tremor, and the shock wave reverberated north up one fault out into Staffordshire, west along another fault to the Lichfield area, and south down a third fault which unbeknown to us ran within a mile of our house .....

Workingman wrote:
What the USGS urgently needs is a way to classify tsunamis in the way we do with typhoons and tornadoes.

Is it not the case with a tsunami that the "effects" of it striking land are pretty much totally dependent on the underwater topography of the place where it actually comes ashore? So what might be a 5m wave here is only a ripple 50 miles further up the coast?