Earthquake Warning Systems

   Saving lives during earthquakes is critically dependent on three major issues: knowing the hazards, planning accordingly, and receiving adequate warning that an earthquake is occurring. During earthquakes seismic waves travel outward from the epicenter, traveling at up to several miles per second. For large earthquakes, significant damage may be inflicted on structures tens or even hundreds of miles from the epicenter, several or several tens of seconds after the earthquake first strikes in the epicentral region. Typically the most destructive surface waves travel more slowly than P and S waves, and at distances of more than a few miles, the time difference can be significant. Earthquake engineers and urban planners are utilizing these basic physical realities to devise and implement some extremely sophisticated earthquake warning systems for places like southern California and Japan. Seismographs are being linked to sophisticated computer systems that quickly analyze the magnitude of an earthquake and determine if it is going to be destructive enough to merit a warning to a large region. If a warning is issued that a large earthquake is occurring, the systems use satellite and computer networks to send a warning to the surrounding areas to immediately take a prescribed set of actions to reduce the damage, injury, and death from the earthquake. For instance, trains may be automatically stopped before they derail, sirens may sound so that people can take shelter, nuclear plants can be shut down, and gas lines can be blocked. These warning systems may be able to alert residents or occupants of part of the region that a severe earthquake has just occurred in another part of the region, and that they have several or several tens of seconds to take cover. The thought is that if structures are adequately constructed, and if people have an earthquake readiness plan already implemented, they will know how and where to take immediate cover when the warning whistles are sounded, and that this type of system may be able to save numerous lives.

   The effectiveness of earthquake warning systems depends on how adequately the plans for such an event were made. Ground shaking causes much of the damage during earthquakes, and the amount of shaking is dependent on the type of soil, bedrock, the geometry or focal mechanism of the earthquake, and how local geologic factors focus the energy to specific sites. Geologists are able to map the different soil and shaking hazard potentials and build a computer-based database that is useful for emergency response. For instance, a type of map known as a shake map may be rapidly generated for specific earthquakes, showing how much shaking might have been experienced in different areas across a region. If the types of buildings and their susceptibility to shaking are known, the consequences of earthquakes in specific neighborhoods can be predicted. Emergency responders can then immediately go to the areas that likely received the most damage, saving lives and helping