"Slow" Earthquakes May Help Predict Major Quakes

Iphtashu Fitz writes "Think all earthquakes last only seconds or minutes? Think again! Scientists at the University of Washington are measuring a "slow" earthquake some 12 to 25 miles underground that could last as long as a month. Along with the UW scientists, seismologists at the Geological Survey of Canada and Central Washington University have documented at least nine previous so-called slow earthquakes going back to 1992. They seem to occur every 14 months or so, the last one occuring in February and March of last year. These earthquakes, also known as slow-slip earthqakes, can release as much energy as a magnitude 6.8 earthquake but because it's released over such a long period of time nobody on the surface even notices it. One key question the scientists are trying to answer is whether these slow earthquakes add to or relieve stress in the tectonic plates, which could ultimately help to predict major earthqakes."

Comments

I think it's scary...

[Mz6]

Considering that the largest earthquake ever in Washington was a 7.3 in 1874 and that this was largely just discovered a few years ago, perhaps this is a precursor to something big about to happen? More recently was a 1949 earthquake that measured 7.1 near Olympia.

From the Science Daily article..."Making that determination will help in understanding whether they are adding to or relieving stress in the Cascadia subduction zone off the Washington and B.C. coast, where the Juan de Fuca plate dives beneath the North American plate. The subduction zone is capable of generating great earthquakes, and scientists recently determined that a Cascadia earthquake in 1700 measured about 9.0 in magnitude."

And Wired... "The coastal region of northwest Washington state and southeast British Columbia is prone to earthquakes, and scientist warn the area gets hit with a devastating shake of magnitude 9 about every 500 years."

Sure.. we're only 196 years off the 500 year mark since the last 9.0, but for it only to pop up a few years ago makes it seem very ominous.

This data, while very interesting, could still go 2 ways. It is helping to alleviate and prevent major earthquakes in that area, or it's a major precurosr to a huge event that could happen in the near future. The hard part? What is considered teh near future... tomorrow? 5 years? 10 years? Guess we'll have to wait and see.

What's even more interesting is that I have yet to see any reports about this coming from any of the California plates, perhaps it hasn't been found or tested for or it's just not there.. Who knows.

Re:I think it's scary...

[TastyWords]

You want scary?

Here in the midwest (Indiana) we're anxiously awaiting the next quake from the New Madrid fault. The last time it peaked, the Mississippi reversed direction for two days and the ground rippled like waves of four-to-five feet.

Imagine that with the fact most buildings in the midwest, whether it's Chicago, St. Louis, any other city familiar to you - if you aren't familiar with all of the cities, haven't been built to withstand an earthquake. After all, they don't come along often enough to warrant that type of concern and|or expense.

Politically Incorrect

[Anonymous Coward]

Do *NOT* call them slow...

...they're "special" earthquakes.

:: ducks ::

Re:Politically Incorrect

[geomon]

These kinds of puns are not gneiss. The are just the type of schist that geologists have been objecting to for years.

Re:Politically Incorrect

[Surlyboi]

Isn't that still politically incorrect?

Yeah, but less so than the original term, "Tardquakes".

More Info Is Always Good

[ackthpt]

The conventional wisdom among my friends and neighbors is, if it has been quiet for too long, it's a bad sign. I've been through a couple 5.0+ earthquakes, the slow rolling type 15-20 seconds and they're pretty nerve wracking, though much preferble to the sudden jolt 3.0+ shockwaves. In Monterey, CA I felt the last 5.4(?) a couple weeks ago down near Paso Robles (probably an aftershock of the 6.5 quake Dec 2003.) As the 2003 illustrates, there are quakes looming in places we're quite unaware until they strike (i.e. Seattle a couple years back), thanks to the complexity of the faults (it's not like there's one fault line, but a who series of fractures along the edge of the plate.) It does seem all the rage of the past few years has been in trying to detect pending quackes along long silent faults, long as in perhaps hundreds or thousands of years.

Still, as far as I have seen the worst to hit North America since europeans settled here struck in a series between 1811 and 1812 near New Madrid, Missouri, one of which reportedly run church bells as far away as Washington DC.

Some day the big one will hit and all the land east of the San Andreas Fault will slide off into the Atlantic Ocean

Better article found

[Mz6]

Interview with a USGS official on "slow" quakes back in 1992. Click here!

Re:Tectonic plates

[geomon]

"Slow" earthquakes are a bit of a misnomer. The energy released in a slow earthquake is the same as the energy released by a catastrophic quake. It is just released over a longer period of time.

General plate movement creates both slow and catastrophic quakes; plate tectonics is the engine driving the stress that creates earthquakes.

Encourage them!!

[sameerdesai]

I believe a research into predicting earthquakes should be encouraged and given more funding. I am saying this because of my own experience. About 3 years ago, my city and lot of cities around my state experienced a major quake reading 7.8 (Bhuj quake in India) that killed more than 30,000 people. I was sleeping when this happened and it was terrifying. Never in my dream I had imagined my city was in earthquake prone zone. Looking at the rumble and bodies gave me shivers. I believe if such a thing is developed so many lives could be saved (if not property). Also this might help in identifying earthquake zones (if I remeber correctly they classify them in zones based on likelihood of having an earthquake) and that can give an impetus to civil authorities to build earthquake proof houses minimising property damage as well. Just my thoughts.

Predictable Earthquakes

[CharAznable]

I'm from Costa Rica, which has its share of earthquakes. Common wisdom states that the earthquake cycle comes around every 30 to 40 years, and the lasts about 10 years. During that time, a couple of >6.0 earthquakes are expected. This works like clockwork. In 1910, an earthquake levelled the city of Cartago. More high profile earthquakes happened in the 50's, then 30 years of silence, and then the new wave started around 1984 and continued into the early 90's. It now appears to have subsided. In 1991, I experienced the might of a 7.1 quake. I almost crapped my pants.

Re:can release as much energy

[ackthpt]

Does this not imply stress is being released?

The thing is, the plate as massive as it is in scale is elastic and these faults, like the San Andreas may run hundreds of miles. When there's a shift it may only move the whole plate a few inches in an area (or even feet in one example north of San Francisco where a fence was warped) that's a lot of mass to move and we're just standing on it like ants. Some pressure relieved in one locaction undoubtably builds pressure somewhere else, or even transfers presure to a parallel fault. This is a particularly good place to start when looking at the scope of things.

Really Scary

[Kozar_The_Malignant]

I was involved in planning for insurance company response to a quake on the New Madrid fault in the early 90's. Living in California, I'm used to quakes and have lived through some bad ones. A quake on the New Madrid fault would be a monumental disaster on many levels. First, as the writer above points out, the building is not to earthquake standards. Damage would be horrific. Places like Memphis would simple cease to exist.

Second, not only are codes inadequate, but the geology of the area contributes to the problem. The solid parent material (bedrock) allows propagation of the energy over a much wider area than in California. The historic New Madrid quakes cause church bells to ring in Boston. This coupled with the fact that many cities and towns are built on alluvial surface material that undergoes liquifaction during a quake means that once the energy reaches a remote area, it will still do a lot of damage.

Third, the extremely high market penetration of earthquake insurance in the commercial and homeowners insurance markets in the midwest means this would be a world-wide financial disaster far exceeding that of the 9/11/01 World Trade Center loss. Earthquake insurance in most midwest states is dirt cheap and has relatively low deductibles. Everybody has it. Here in California, it is expensive and has very high deductibles. Most people don't have it. If you do the math here, you are better off putting the money you would spend on premiums into mitigation efforts like foundation bolts, masonry reinforcements, etc. Our calculations in the 90's on the dollar loss from a repeat of the New Madrid quakes indicated that a Great Depression style financial collapse was not just possible, but likely.

This is seriously scary shit. The New Madrid Earthquake scare has passed, and not too many people in the midwest are doing any real earthquake planning. The next quake on the New Madrid fault will happen, we just don't know when.