Earthquake Sensors: Theory and Practical Applications
An Earthquake Alert System (EAS) could give several seconds to several tens of seconds warning before the strong motion from a large earthquake arrives. Such a system would include a large network of sensors distributed within an earthquake-prone region. The sensors closest to the epicenter of a particular earthquake would transmit data at the speed of light to a central processing center, which would broadcast an area-wide alarm in advance of the spreading elastic wave energy from the earthquake. This is possible because seismic energy travels slowly (3 to 6 km/s) compared to the speed of light (Real-time earthquake monitoring, 1991).
Utilities, public and private institutions, businesses, and the general public would benefit from an EAS. For example:
1. Facilities with high energy or high precision machinery could be shut down before strong motion arrives (e.g., power plants, power distribution centers, refineries, factories, and computer systems).
2. Airport operations could be suspended, hospitals alerted, and trains stopped.
3. Fire station doors could be opened.
4. Emergency generators could be turned on.
5. Emergency services could be deployed.
6. Audio alarms could alert people and perhaps give the extra time needed to move to a place of relative safety in the immediate area.
Although many earthquake protection systems exist that automatically shut down power, gas mains, etc. when ground motion at a facility reaches damaging levels, no EAS -- that is, a system that can provide warning in advance of elastic wave energy arriving at a facility -- has ever been developed in the United States (Real-time earthquake monitoring, 1991).
The idea for sensing earthquakes has been around for quite a while, as noted by the telling quote below:
A very simple mechanical contrivance can be arranged at various points from 10 to 100 mil...