Someplace on earth the ground is shaking. According to USGS estimates, there are an average of 1,300,000 earthquakes on our planet every year, or one every 24 seconds. 98% of those quakes are under magnitude 4.0 and many occur in remote locations, so most of us are unaware of the constant seismic activity, even when it happens close by.
However between 1,500 and 2,000 annual quakes are in the magnitude 5.0 to 9.0 range. Those are the quakes that can do damage on land, and possibly trigger a tsunami if one strong enough hits on the seafloor where tectonic plates converge.
Where do USGS and other reporting centers get their real time information? Two worldwide seismic hazard networks report earthquakes as they happen, and provide early warning when a tsunami starts rolling toward land.
Global Seismographic Network (GSN) is a permanent digital network of 150 land-based and ocean-bottom seismometers positioned in earthquake prone locations around the world, and connected by a telecommunications network. GSN is a partnership among USGS, the National Science Foundation, and Incorporated Research Institutions for Seismology (IRIS), a consortium of 100 worldwide labs and universities. Although US based, GSN is fully coordinated with the international community. GSN stations are operated by USGS and UC San Diego. The network determines location and magnitude of earthquakes anywhere in the world as they happen. The data is used for emergency response, hazard mitigation, research, and tsunami early warning for seafloor locations.
Deep Ocean Assessment and Reporting of Tsunamis (DART) is the main component of an international tsunami warning system. The DART system is based on instant detection and relay of ocean floor pressure changes. DART stations consist of an ocean bottom sensor that picks up changes in pressure as the tsunami wave passes and sends the data to a nearby communications buoy, which transmits it to a satellite, which in turn relays it within seconds to tsunami warning centers around the world.
The US has deployed 39 DART stations in the Pacific, Atlantic, and Caribbean. Australia and Peru have also installed DART systems, and since the 2004 Indian Ocean tsunami that killed over 200,000 people, the nations bordering the Indian Ocean have cooperated in the installation of 6 Indian Ocean DART stations, along with 17 seismic satellite stations. The DART data, along with GSN and satellite data, flow into two major tsunami warning centers: the Pacific Tsunami Warning Center in Ewa Beach, Hawaii, and the West Coast and Alaska Tsunami Warning Center in Palmer, Alaska. It is the job of the tsunami warning centers to issue alerts and warnings to population centers in the path of a developing tsunami.
Although the GSN and DART systems have proved effective, NASA is testing a GPS system that can spot the epicenter location and earthquake magnitude 10 times faster, giving those in peril extra seconds and minutes to evacuate before the tsunami strikes land. NASA is still testing the system.