May 05, 2003
Posted on 05/04/2003 11:13:07 PM PDT by Pro-Bush
May 05, 2003
Earthquake Warning System Sounds Alarm Seconds before Tremors Begin
Most seismologists agree that predicting earthquakes days in advance is not going to be possible anytime soon. But borrowing from a system developed in Japan, scientists have devised an early warning system that will alert southern California residents seconds before a temblor begins. When an earthquake strikes, the first pulse of energy to radiate from the point of origin comprises primary (p) waves. P waves travel about two times as fast as the secondary (s) waves that follow them and that carry the destructive, ground-shaking power characteristic of large quakes. The s waves are traditionally used to assess the magnitude of an event, but this information is only gleaned after the fact. The new system measures the first waves to arrive -- the p waves -- and thus provides warnings up to tens of seconds before the ground begins to move. That might seem like a negligible amount of time, but it's enough to take cover beneath a table or shut off gas lines and water mains.
Richard Allen of the University of Wisconsin and Hiroo Kanamori of the California Institute of Technology describe the system, called ElarmS, today in the journal Science. They developed ElarmS using historical earthquake data collected by an array of sensors spread throughout southern California. Measuring the frequency content of the p waves allowed Allen and Kanamori to figure out what the damage potential from a given quake might be at any point in the region. The system works because smaller earthquakes tend to send out high-frequency p waves whereas large-magnitude events radiate lower frequency energy.
ElarmS is designed to detect earthquakes small and large, because "only if it works for small magnitude events can we be sure the system is operational," Allen says. "If we're only looking at magnitude-6 earthquakes we'd only be testing every 30 years or so, and that's not practical." Now those seismologists that run southern California's already-established network of sensors, TriNet, are integrating Allen and Kanamori's computer program into their system. ElarmS will be tested using real-time data from small earthquakes over the coming years. Allen believes it will be most useful in developing safer automated transportation systems, buildings and city infrastructure that can be programmed to react to incoming p waves. "It is perhaps not reasonable to expect people to respond to an alarm they hear once every 30 years," he says, "but we have the potential now to build infrastructure that responds to these warnings and protects occupants." --Laura Wright
The velocity of P-waves depends on the medium through which they travel. P-waves are compressional waves that can travel through solids or fluids. A sound wave is a form of P-wave. S-waves, on the other hand, can only be propogated through solids.
P-waves travel through typical clastic sedimentary rocks at velocities of 5,000 feet per second to 8,000 feet per second (fps). When they travel through "harder" rocks, such as granite, the velocity may be over 10,000 fps. When they travel through ocean water, the velocity is about 4,900 fps.
Some people claim that they can "hear" an earthquake coming. Since the frequency of earthquakes are generally below the audible range of human hearing, the claim is dubious. However, the person experiencing the first P-waves arrivals may not yet realize they are at the beginning of a quake, and may only become aware when the more violent S-wave arrives.
The "intensity" of an earthquake generally diminishes with its distance away from the hypocenter (the hypothetical point inside the earth, below the "epicenter," where the earthquake "starts"). Of course, this can change with local geological variations. Earthquake warning systems based on sensing P-wave arrivals don't react quickly enough near the epicenter of the quake, and don't make much difference at points distant from the epicenter.
Sounds kinda goofy..but all over the quake area...owners of fish in fish tanks saw bizzare behaviour exhibited by the fish...and at a considerable time interval ahead of the quake..like an hour or more.
The fish began to swim like they needed to get away....the onlookers saw their fish slam into the glass..and keep on slamming like some primal alert thing had gone off.
They are doing R and D as to what energy emmision is trippin the fish.
When I was young..there was this movie called Earthquake .
The theatre we visited had these cheesy speakers set up on the floor with some resonance effect..supposedly the harmonics recorded from real earthquakes.
The theatre went bananas when the system kicked in on que with some of the scenes.
Some ran out of the theatre and never came back.
I believe they pulled the soundsystem out ..and just showed the film..as lawsuits began to appear.
The sound of a large earthquake coming is more scary to me then the actual movement of the ground. That sound can not be reproduced by any sound system, it is an amazingly extremely deep thundering type of sound.
He did these works in the 50's..using Mythology and records of known Kings and kingdoms of antiquity.
Many stories appear from these ancient cultures....alligned to earthquakes,volcanic erruptions etc.
Some records convey the theme of the earth groaning...like a voice.
From China to the Mid east..the comment.."When will the earth stop groaning....when will it be quiet"
the sound emmision from the earth below recorded to have gone on for weeks.
That sound in the movie was as close as any sound system can get I think to the actual earthquake sound.
But the real earthquakes I remember were a little differnet, you know how a VERY large base sound feels on your body? It is like that but it isn't as loud as the movie.
I am surprised it took this long for them to come up with a system that hears it comming. Hrmm..
SENSURROUND was a patented special effects system that generated powerful infrasonic shockwaves in a theater and also allowed 70+db dynamic range and surround sound from a mono optical print. Orignally, for the film EARTHQUAKE, it used an external noise (rumble) generator that was programmed to duplicate the waveform of the 1971 Sylmar quake in California.
There's lots more tech discussion in that post, by the way.
Regards
Sadim
The thundering part of the train yeah. that is close but MUCH more powerful. You can just feel the power in the sound. I don't remember it being 'loud' untell it was shaking the house.
There was a 5.0 earthquake near where I live now. I heard it coming funny thing is I knew approximately how big it was going to be by the sound that was coming. It was a estimated guess but I was right hehe.
The B/W photos of the 64 Alaska quake are powerfull too.
I heard one, so it doesn't seem so dubious to me. I was out in the boonies, camping in the Sierras, and it was very quiet... and it was at night, as we were all in bed, so it was pretty quiet. Then there was a rumbling noise, and then a couple seconds later I was shaking.
Neil Boortz, the talk radio host, said he was in the shower when it struck at 5am. He heard a strange sound and had no idea what it was until later.
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