The Earth might have a more turbulent past—and hence a more turbulent future—than we thought. In a presentation yesterday, Dr. Susan Hough of the US Geological Survey argued that hidden throughout history are a glut of giant earthquakes that either went unrecorded or have been underestimated. "Seismometers were developed around 1900. As soon as we had them, earthquakes started to look bigger," Hough said. To wit, LiveScience reports that records show that three temblors registered above magnitude-8.5 in the 19th century; the 20th century claims a dozen.
Her theory is that earlier earthquakes in the 8.0 to 8.5 magnitude range were actually bigger than that. "If you try to make a statistical case, there are too few earthquakes in the 19th century," she says. She found evidence that many 19th-century quakes were likely bigger than we thought, the BBC reports. One 1843 quake, for example, was recorded as magnitude-8.3. "It turns out it was felt by a quarter of the globe." This matters, because these historical quakes can help us predict future ones. The upshot being that the risk of future "big one" quakes is likely higher than we've been assuming.