A magnitude-7.1 earthquake struck Chile on Jan. 2, 2011, or so scientists thought. Now, with increasing sensor sensitivity and advances in the quantitative analysis of earthquakes, scientists have revealed that this quake was actually a doublet. This meant that instead of just one massive quake, two similarly large earthquakes struck very near to one another within seconds. The closely spaced doublet was missed by global monitoring networks during the initial aftermath of the quake, and, as EARTH Magazine explores, it presents a major challenge to earthquake and tsunami warning systems. Experts agree this is a challenge that must be brought to the forefront of seismic research.