In the course of a year, the National Earthquake Information Center, the arm of the United States Geological Survey (USGS) responsible for tracking and sharing information about earthquakes worldwide, reports approximately 30,000 events. That’s an average of 80 earthquakes a day, a number made even more impressive by the fact that it represents only the most significant of the Earth’s constant movements: quakes with magnitudes of 3.0 or higher, a tiny fraction of the many millions of earthquakes that the USGS estimates occur annually.
Feeding this massive data collection effort are national and global seismic networks, which rely on hundreds of instruments like the compact, stainless steel seismometer pictured here. This 14-inch-tall model currently takes measurements of Earth’s vibrations at stations from Albuquerque, New Mexico, to Santo Domingo, Venezuela, then transmits the information digitally, making rapid earthquake alerts—and prompt mobilization of aid by government and humanitarian agencies—possible.
The ability to detect and locate earthquakes has been more than 1,800 years in the making. The earliest known seismic instrument dates back to AD 132, an invention of the Chinese polymath Zhang Heng. It was designed as an urn decorated with eight dragon heads, each holding a ball. Eight open-mouthed toads circled the base, and though the exact mechanism is unknown, seismologists think a pendulum inside the vessel was used to sense ground movement, which would trigger one of the balls to drop from dragon to toad to reveal the direction of an earthquake’s waves. The instrument was said to have accurately detected an earthquake hundreds of miles away from the imperial court.
See a digital seismometer and a seismograph drum in Nature’s Fury: The Science of Natural Disasters.
A version of this article appears in the Fall 2014 issue of Rotunda, the Member magazine.