9:59:59.000,9:59:59.000 In 132 CE, 9:59:59.000,9:59:59.000 Chinese polymath Zhang Heng 9:59:59.000,9:59:59.000 presented the Han court with [br]his latest invention. 9:59:59.000,9:59:59.000 This large vase, he claimed, 9:59:59.000,9:59:59.000 could tell them whenever an earthquake [br]occurred in their kingdom– 9:59:59.000,9:59:59.000 including the direction [br]they should send aid. 9:59:59.000,9:59:59.000 The court was somewhat skeptical, 9:59:59.000,9:59:59.000 especially when the device triggered [br]on a seemingly quiet afternoon. 9:59:59.000,9:59:59.000 But when messengers came [br]for help days later, 9:59:59.000,9:59:59.000 their doubts turned to gratitude. 9:59:59.000,9:59:59.000 Today, we no longer rely on pots to [br]identify seismic events, 9:59:59.000,9:59:59.000 but earthquakes still offer a unique[br]challenge to those trying to track them. 9:59:59.000,9:59:59.000 So why are earthquakes so [br]hard to anticipate, 9:59:59.000,9:59:59.000 and how could we get better [br]at predicting them? 9:59:59.000,9:59:59.000 To answer that, 9:59:59.000,9:59:59.000 we need to understand some theories [br]behind how earthquakes occur. 9:59:59.000,9:59:59.000 Earth’s crust is made from several vast, [br]jagged slabs of rock 9:59:59.000,9:59:59.000 called tectonic plates, 9:59:59.000,9:59:59.000 each riding on a hot, partially molten[br]layer of Earth’s mantle. 9:59:59.000,9:59:59.000 This causes the plates to [br]spread very slowly, 9:59:59.000,9:59:59.000 at anywhere from 1 to 20 [br]centimeters per year. 9:59:59.000,9:59:59.000 But these tiny movements are powerful [br]enough 9:59:59.000,9:59:59.000 to cause deep cracks in the[br]interacting plates. 9:59:59.000,9:59:59.000 And in unstable zones, 9:59:59.000,9:59:59.000 the intensifying pressure may [br]ultimately trigger an earthquake. 9:59:59.000,9:59:59.000 It’s hard enough to monitor these [br]miniscule movements, 9:59:59.000,9:59:59.000 but the factors that turn shifts into [br]seismic events are far more varied. 9:59:59.000,9:59:59.000 Different fault lines juxtapose [br]different rocks– 9:59:59.000,9:59:59.000 some of which are stronger–or weaker–[br]under pressure. 9:59:59.000,9:59:59.000 Diverse rocks also react differently to[br]friction and high temperatures. 9:59:59.000,9:59:59.000 Some partially melt, and can release[br]lubricating fluids 9:59:59.000,9:59:59.000 made of superheated minerals 9:59:59.000,9:59:59.000 that reduce fault line friction. 9:59:59.000,9:59:59.000 But some are left dry, 9:59:59.000,9:59:59.000 prone to dangerous build-ups of pressure. 9:59:59.000,9:59:59.000 And all these faults are subject to [br]varying gravitational forces, 9:59:59.000,9:59:59.000 as well as the currents of hot rocks[br]moving throughout Earth’s mantle. 9:59:59.000,9:59:59.000 So which of these hidden variables [br]should we be analyzing, 9:59:59.000,9:59:59.000 and how do they fit into our [br]growing prediction toolkit? 9:59:59.000,9:59:59.000 Because some of these forces occur [br]at largely constant rates, 9:59:59.000,9:59:59.000 the behavior of the plates [br]is somewhat cyclical. 9:59:59.000,9:59:59.000 Today, many of our most reliable clues [br]come from long-term forecasting, 9:59:59.000,9:59:59.000 related to when and where earthquakes [br]have previously occurred. 9:59:59.000,9:59:59.000 At the scale of millennia, 9:59:59.000,9:59:59.000 this allows us to make predictions [br]about when highly active faults, 9:59:59.000,9:59:59.000 like the San Andreas, 9:59:59.000,9:59:59.000 are overdue for a massive earthquake. 9:59:59.000,9:59:59.000 But due to the many variables involved, 9:59:59.000,9:59:59.000 this method can only predict [br]very loose timeframes. 9:59:59.000,9:59:59.000 To predict more imminent events, 9:59:59.000,9:59:59.000 researchers have investigated the [br]vibrations Earth elicits before a quake. 9:59:59.000,9:59:59.000 Geologists have long used seismometers 9:59:59.000,9:59:59.000 to track and map these tiny shifts[br]in the earth’s crust. 9:59:59.000,9:59:59.000 And today, most smartphones are [br]also capable 9:59:59.000,9:59:59.000 of recording primary seismic waves. 9:59:59.000,9:59:59.000 With a network of phones around the globe, 9:59:59.000,9:59:59.000 scientists could potentially [br]crowd source a rich, 9:59:59.000,9:59:59.000 detailed warning system that alerts [br]people to incoming quakes. 9:59:59.000,9:59:59.000 Unfortunately, phones might not be able[br]to provide the advance notice needed 9:59:59.000,9:59:59.000 to enact safety protocols. 9:59:59.000,9:59:59.000 But such detailed readings would still be [br]useful 9:59:59.000,9:59:59.000 for prediction tools like NASA’s [br]Quakesim software, 9:59:59.000,9:59:59.000 which can use a rigorous blend of [br]geological data 9:59:59.000,9:59:59.000 to identify regions at risk. 9:59:59.000,9:59:59.000 However, recent studies indicate 9:59:59.000,9:59:59.000 the most telling signs of a quake might be[br]invisible to all these sensors. 9:59:59.000,9:59:59.000 In 2011, 9:59:59.000,9:59:59.000 just before an earthquake struck [br]the east coast of Japan, 9:59:59.000,9:59:59.000 nearby researchers recorded surprisingly [br]high concentrations 9:59:59.000,9:59:59.000 of the radioactive isotope pair [br]radon and thoron. 9:59:59.000,9:59:59.000 As stress builds up in the crust right [br]before an earthquake, 9:59:59.000,9:59:59.000 microfractures allow these gases [br]to escape to the surface. 9:59:59.000,9:59:59.000 These scientists think that if we built [br]a vast network of radon-thoron detectors 9:59:59.000,9:59:59.000 in earthquake-prone areas, 9:59:59.000,9:59:59.000 it could become a promising [br]warning system– 9:59:59.000,9:59:59.000 potentially predicting quakes [br]a week in advance. 9:59:59.000,9:59:59.000 Of course, 9:59:59.000,9:59:59.000 none of these technologies [br]would be as helpful 9:59:59.000,9:59:59.000 as simply looking deep inside [br]the earth itself. 9:59:59.000,9:59:59.000 With a deeper view we might be able 9:59:59.000,9:59:59.000 to track and predict large-scale [br]geological changes in real time, 9:59:59.000,9:59:59.000 possibly saving tens of thousands [br]of lives a year. 9:59:59.000,9:59:59.000 But for now, 9:59:59.000,9:59:59.000 these technologies can help us prepare [br]and respond quickly to areas in need– 9:59:59.000,9:59:59.000 without waiting for directions [br]from a vase.