Sep 25th 2008
From The Economist print edition
How to use your laptop to locate an earthquake
IF YOU drop your laptop computer, a chip built into it will sense the acceleration and protect the delicate moving parts of its hard disk before it hits the ground. A group of researchers led by Jesse Lawrence of Stanford University are putting the same accelerometer chip to an intriguing new use: detecting earthquakes. They plan to create a network of volunteer laptops that can map out future quakes in far greater detail than traditional seismometers manage.
Seismometers are large, expensive beasts, costing $10,000 or more apiece. They are designed to be exquisitely sensitive to the sort of vibrations an earthquake produces, which means they can pick up tremors that began halfway around the world. By contrast, the accelerometer chips in laptops, which have evolved from those used to detect when a car is in a collision and thus trigger the release of the airbags, are rather crude devices. They are, however, ubiquitous. Almost all modern laptops have them and they are even finding their way into mobile phones. The iPhone, for example, uses such a chip to detect its orientation so that it can rotate its display and thus make it easily readable.
On its own, an accelerometer chip in a laptop is not very useful for earthquake-detection, as it cannot distinguish between a quake and all sorts of other vibrations—the user tapping away at the keyboard, for example. But if lots of these chips are connected to a central server via the internet, their responses can be compared. And if a large number in a particular place register a vibration at almost the same time, it is more likely to be an earthquake than a bunch of users all hitting their space bars. To exploit this group effect, Dr Lawrence’s Quake-Catcher Network (QCN) employs the same software that is used by the SETI@home project, which aggregates computing power from hundreds of thousands of volunteer computers around the world to analyse radio-telescope signals for signs of extraterrestrial intelligence.
Dr Lawrence and his colleagues have already demonstrated that the QCN works. It detected a quake near Reno, Nevada, in April, and one near Los Angeles in July. Merely detecting a quake, however, is not the point. Seismometers can do that. To be useful, the QCN needs to be able to do things that seismometers cannot.
One of those things is to measure the maximum amount of ground shaking. The sensitivity of seismometers means that strong signals would damage them if they were not designed to “clip” such signals when they exceed a certain threshold. The price paid is that information about strong, nearby earthquakes is lost. Laptop accelerometers are more robust. Though they cannot, if in America, tell you anything about an earthquake in China, they can sometimes do better than conventional kit when measuring local quakes.
The network’s second benefit is of sheer numbers. This should allow the construction of far more detailed maps of the up-and-down and side-to-side motions induced by earthquakes. These vary a lot from quake to quake, and that means the damage done by a quake of any given strength is also variable. A better understanding of how movement and damage relate might help both building design and town planning in earthquake zones.
Of course, for that to work, you have to know where each laptop was at the moment of the quake. Ideally, this information would come from a Global Positioning System device fitted within the laptop, but few computers have them at the moment. In their absence, information automatically supplied about the site of the nearest router (a network device that computers use to connect to the wider internet) gives a rough location. This is imperfect, but pooling the data from lots of laptops means that location errors can be detected statistically and erroneous data discarded.
If that can be done quickly enough, the QCN could bring a third—and most valuable—benefit: warning. The speed of internet communication, coupled with a scheme for uploading data from each computer at brief intervals, means that Dr Lawrence’s network could issue an earthquake warning within seconds. That is faster than traditional seismometer networks, which update less regularly, and, above all, is much faster than seismic waves travel. Warnings could thus be broadcast to places the earthquake waves had not yet reached, giving people vital time to find a place of refuge.
At the moment, the QCN has about 1,500 participating computers. But, as happened with SETI@home, the researchers expect numbers to grow once knowledge of the project spreads: qcn.stanford.edu, for those who want to join in the fun.