"Earthquakes pose significant risk to 75 million Americans in 39 States. The USGS is the only Federal agency with responsibility for recording and reporting earthquake activity nationwide. Citizens, emergency responders, and engineers rely on the USGS for accurate and timely information on where an earthquake occurred, how much the ground shook in different locations, and what the likelihood is of future significant ground shaking.
The USGS estimates that several million earthquakes occur in the world each year, but many go undetected because they occur in remote areas or have very small magnitudes. The USGS now locates about 50 earthquakes each day; 20,000 a year."