Earthquake and tsunami warning systems both monitor the same thing: seismic waves. Seismic data takes the Earth's pulse directly, so when the earth shakes, we get immediate feedback. If all goes well, we have enough time to run.
Lots of organisations watch for earth movement. The US's Advanced National Seismic System (ANSS), for instance, runs 95 stations across North America. When there's an earthquake, ANSS sends out a signal in real time, which alerts government agencies and emergency response personnel.
Earthquakes on land are serious business, to be sure, but responding to them is fairly straightforward: direct the appropriate resources to the place where the alarm bell rang the loudest. But when earthquakes cause tsunamis, an international effort is usually required. Think about it: An earthquake under the sea doesn't just cause a killer wave directly above it. Landmasses shift, water is displaced and, depending on several other factors, it could end up anywhere.
Seismic waves travel 100 times faster than ocean waves, so you have to take the Earth's movement into account to figure out when the wall of water will hit land. To understand just how important it is to use seismic data to get people safe, you only need to look back to the magnitude-9.0 Indonesian quake of 2004. The Indian Ocean had no early warning system in place, and the tsunami triggered by the earthquake killed 200,000 people in 11 countries - including 30,000 people in Sri Lanka, 1600km away from the epicentre. Information just didn't get to the people who needed it fast enough.
But today, when the 8.9 hit, the Japan Meteorological Agency issued a major tsunami warning within three minutes of the event. Six minutes after that, Islands in the South pacific, Hawaii and Russia were told to watch their shores. The collaborating systems are a part of the Intergovernmental Oceanographic Commission run by UNESCO, which organizes international disaster response.
Japan is hyperaware of its shaky ground. The country withstands some thousand tremors a year, and they've got 180 seismographs and 600 seismic intensity meters constantly tuned to what's going on in the underworld. They also have around 30 sea level gauges operated by the coast guard and around 80 operated by the JMA that work in chorus to provide feedback to a Data Processing and Communication system. The sensors take a reading, upload it to a central processing system using old-fashioned wires and/or satellite uplink, and that central system sends updates to the government, police, coast guard, telephone companies, and the media. Sea level gauges also report disturbances in real time and help organisations model trajectory and size of the oncoming waves.
And then there are more specialised tools. The NOAA, for instance, has a handful of tsunami detection buoys that help rule out false alarms and give monitoring agencies a better idea of what they're in for - or what their not. NOAA's Deep Ocean Assessment and Reporting of Tsunami system - which goes by the slick moniker 'DART' - is made up of an anchored sea floor bottom pressure recorder and accompanying fiberglass and foam buoy on the surface. The recorder on the ocean floor, which takes a note of temperature and pressure every 15 seconds, sends data via an acoustic link to the surface buoy. The buoy then sends information by satellite to Tsunami warning centres.
How does the information get to you? Warning systems coordinate with the media. That's how you got the information on your front page. To get even faster info, in many places you can sign up for text alerts if something disastrous is happening-or will happen, in the case of a tsunami-in your area.
Curious, confused, or just, y'know, interested in... interesting stuff? You can suggest things that we should explain by emailing us at [email protected]
Lead photo courtesy flickr user gfreeman23; other images courtesy USGS.