Sunday, March 27, 2011

Earthquakes - Past, Present, and Future

In the aftermath of the March 11th disaster in Japan, the topic of the earthquake is still making headlines.  I’m not going to talk about the Japanese earthquake much here, because it’s been done a thousand times by now, and by better-informed people than myself.  One of those people is Donald Prothero, who wrote up a very thorough description of the event.

But let’s talk about earthquakes.  Anyone who knows earthquakes will tell you that they are dangerous and terrifying for two main reasons.  First, they can be incredibly powerful and extremely destructive, and we’ve seen examples of this countless times.  And second, they are largely unpredictable.  Our instruments often determine that a big quake is coming only seconds before it hits.  Despite decades of study, an accurate predictive model for earthquakes still remains the unachieved holy grail of seismology.

But a new study from researchers in Tel Aviv is a step in the right direction.  Actually, at first glance it sounds more like a step in the opposite direction.  Instead of working on a model to predict earthquakes in the future, they’re developing a model to study earthquakes of the distant past.

This is what typical
lake sediments look
like - nice flat layers
How does it work?   The Tel Aviv scientists are looking at lake sediments at the Dead Sea.  Layers of mud and dirt are laid down flat under water, but the layers of mud at the Dead Sea show peculiar deformations – irregularities in the arrangement of the layers.  Where do these strange structures come from?  Earthquakes.  The shaking of the earth during earthquakes in the past disturbed the otherwise nice orderly layers of sediment, leaving patterns of disruption that we can still see today.  These scientists were able to develop a model that can interpret the deformation of the sediment layers to tell us some things about earthquakes from the past: when they happened, where they happened, and how strong they were.  After some improvement, this model may be able to say something like, “A 5.1 earthquake happened right here 314 years ago.”

So what does this mean for the study of earthquakes?  Well, it means a couple of things.  First, this model will offer a new method of understanding events in the past, and that’s always exciting.  Any area that has lake sediments near an active fault zone (California, South America, or Japan, for example) can be a potential site for the study of “earthquake fossils,” as ScienceDaily calls them.

Where do earthquakes happen? The most earthquake-prone areas on the planet
are around the edges of the Pacific Ocean.

But even more relevant in light of recent events, this study will take advantage of one of the cornerstone themes in modern geology – “The past is the key to the future.”  If we want to predict what earthquakes will do in the future, we need to know more about what they’ve done in the past – what causes them, and what patterns we can expect to see from them.

The media has offered us a number of creative ideas about the causes and patterns of recent earthquakes.  Some people argue it’s a sign of the apocalypse (we can thank the Mayans for that one), while others are blaming the moon.  Both of these are utter nonsense, but that hasn’t stopped them from spreading around the internet like wildfire.
A third conspiracy theory comes from a man writing for Newsweek who predicts that the Japan earthquake is the precursor to another earthquake of equal if not greater devastation that will strike California any day now.  This is another ridiculous bit of over-hyped pseudo-science (see here for real science), but it does raise an interesting question – are big earthquakes related to each other somehow?

Some scientists think they might be.  Between the Sumatran earthquake of 2004, the Chilean earthquake in 2010, and the Tohoku earthquake this year, there seems to be quite a lot of big activity going on in a short amount of time.  Models predict that big earthquakes should happen much more infrequently.  Is it possible that one big earthquake might set off some sort of chain reaction that can lead to other big earthquakes?

Seismic waves from an earthquake
travel all throughout the planet
Well, the jury’s out on that one.  It is definitely true that an earthquake could potentially have an effect elsewhere in the world.  Earthquake waves don’t just travel along the surface and knock down buildings, they travel throughout the entire planet (this is why a seismometer in the U.S. can sense an earthquake in China).  The NewScientist article linked above provides a quote from Ross Stein of the USGS which I absolutely love:

“If you have a quake of, let's say, 6.2 or larger, every sand grain on the planet is moving to the music of that event."

True that, Dr. Stein.

But whether or not that means one big earthquake can cause another a year later on the other side of the world is not certain.  Personally, I would lean toward the side of the argument that says we really don’t have enough data to know.  Our earthquake-reading technology only goes back about a century, so we only know the patterns of earthquakes for the last 100 years.  Three big quakes over several years isn’t really a statistic impressive enough to warrant concern.

But that is where the fossil seismograph comes in.  If this model is successful, we’ll be able to extend our record of earthquakes back much further than a mere hundred years.  Studying patterns of earthquake activity in the past will grant us much greater predictive power for earthquakes in the future.  The day may not be too far off when we’ll be able to forecast earthquakes like the weather.  It’s a very exciting prospect.

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