Earthquake early warning systems help.
Japan
On December 7, 2012, a 7.3 magnitude earthquake struck approximately 150 miles offshore of the northeast coast of Japan. Seconds after the first shock wave, notice was sent nationwide of an impending major earthquake. Subsequently, television and radio stations interrupted programming to broadcast the message and warnings. Messages were sent via text to cellular phones. Thus, Tokyo residents had a full six minutes of warning before the first seismic tremors were felt. This was the first time an early warning system had been successfully used to warn the public of an imminent major earthquake.
After the devastating 6.9 magnitude Kobe earthquake of 1995, Japan invested $1 billion in research and development. The country’s meteorological agency implement its earthquake early warning systems in December 2007. So, when an earthquake strikes, seismographs near its source detect the first seismic waves. Those are known as primary or “P” waives.
P-waves are followed by more powerful secondary “S” waves. Those propagate outward from the earthquake’s epicenter, travelling more slowly than P-waves, but with much more potential for damage. The meteorological agency’s computer system analyzes the P-waves and estimates the intensity of the S-waves. Consequently, if the S-waves are deemed to be powerful enough to warrant alerting the public the system issues a warning automatically.
Currently, Japan still employs the most sophisticated EEW in the world.
United States
In the U.S., Earthquake Early Warning (EEW) systems are being developed for the western region of the country. Starting in 2006, the United States Geological Survey (USGS) assembled expertise from:
- Caltech (California Institute of Technology),
- CGS (California Geological Survey),
- CalOES (California Office of Emergency Services),
- University of California, Berkeley
- University of Washington,
- the Gordon and Betty Moore Foundation, and
- University of Oregon.
The goal is an effective EEW system for high risk areas in the U.S. Like the Japanese system, the US system utilizes seismic networks to monitor daily seismic activity to detect potentially destructive earthquakes based upon assessment of initial P-waves.
EEW System
ShakeAlert is a demonstration EEW system. It began testing in California in January 2012. ShakeAlert detects earthquakes via the California Integrated Seismic Network (CISN). This is a current network of ground motion sensors. Effectively, CISN is partnership of groups (many of the above listed organizations) and one of seven regional networks involved in the Advanced National Seismic System (ANSS).
Strong seismic activity travels at a speed of approximately 2 miles per second. So, it is conceivable to detect the source of a large earthquake and transmit a warning to more distant areas before the shaking arrives.
Virtually, an EEW system on U.S. west coast could give government agencies, transportation systems, and citizens as much as 60 seconds of advanced warning before feeling ground movement. Granted, some of that depends on the location of the epicenter and where the shake is detected. However, seismic waves are measured as a frequency (sound speed). Seismic waves travel slower than the internet or phone systems (light speed). So, theoretically, it is possible to detect the start of an earthquake and quickly send a warning out to locations farther away.
For a wonderful explanation, please watch the (non-political) video from MSNBC’s Rachel Maddow show:
