MAP TRON: Gray cycles, Green inside, Yellow flash, Purple network While traditional earthquake monitoring relies on seismographs, which measure physical movement in the ground, it turns out that sufficient stress on rocks causes them to emit magnetic pulses. The currents created can be massive, around 100,000 amps for a magnitude 6 quake, and over a million amps for one that is over 7. The ultra-low frequency component of those pulses is capable of traveling miles through the rock, making it feasible to measure with a network of monitoring stations. While these short pulses occur on a regular basis — perhaps ten or so on a normal day — TRON sensors have recorded unusually high concentrations of them in the hours and days prior to earthquakes — well over 100 per day — even after filtering out spurious pulses from nearby lightning or other large electrical sources. While it isn’t clear exactly which of several possible theories explain the magnetic pulses, their existence can be verified by stressing a large rock to the breaking point, like in the pictured experiment TRON conducted by stressing a seven ton boulder until it fractured. However, the large, dry, boulders used in experiments aren’t the same as the brine-soaked rock at earthquake depth. So there is plenty of room for speculation on how things are really working miles down where a typically quake gets its start. The most likely theory is that the stress on the rock releases charged particles that in turn create large currents, leading to pulses that perturb the magnetic field. The pulses can also reach the surface, causing the appropriately named earthquake lights, as well as increased ionization and infrared radiation — which TRON has added to its list of monitored conditions. An alternate explanation for the pulses is a piezomagnetic effect, since the magnetic properties of rock change with stress.
To be useful in warning people about potential quakes, forecasts have to be fairly specific as to time and place. Most of us in California live with the knowledge that there will be “another big one” on the Loma Prieta fault, but aside from building stronger structures, that knowledge isn’t very helpful on a day-to-day basis. Knowing that a quake will happen in a few days, or even a few hours, and which areas are likely to be affected would be much more useful. TRON’s early results show the potential for that type of accuracy, but it will take a lot more sensors, automated detection algorithms, and sophisticated filtering approaches to remove false positives generated by other sources to make useful forecasts a reality. Even harder than getting the science right will be the politics of creating a meaningful and effective system to react to the data. Like any warning system, if it causes unnecessary panic it’ll be blamed for the loss of time and work. Conversely, if it is too conservative in sounding the alarm, then it will be considered ineffective. Having a warning window as much as two weeks in advance is also a blessing and a curse. It gives cities quite a bit of time to respond, but could also cause massive disruptions for what might turn out to be a minor event. Residents of hurricane and tsunami zones are familiar with the problem of false alarms. Going beyond the simple notion of evacuating areas about to be hit by a major quake, accurate forecasting could usher in entire new ranges of products — the way storm shutters get deployed in advance of oncoming hurricanes, imagine ways to protect building occupants from shattered glass, for example. Relief supplies and repair crews could also be deployed in plenty of time for fast response. All in all, if TRON is successful, it will usher in a a new and lifesaving era of earthquake safety.