In real-time monitoring, signals from seismic sensors in the field (either analog or digital) aretelemetered to a central receiving station for processing. By real-time we mean that the results can be obtainedwithin seconds or tens of seconds. In practice, there are several obstacles to achieving a quicker response. Largeearthquakes normally occur at depth of a few tens of kilometers or deeper. It takes several seconds for seismic
waves to reach the earth‗s surface where the seismic sensors are located, and several tens more seconds before
sufficient numbers of sensors detect the seismic waves. In the experimental earthquake early warning system inHualien, Taiwan, a 10-second or less response time has been achieved for earthquakes 5 occurring inside or near the dense array with sensor spacing of about 2 km. However, such dense deployment of sensors is noteconomical to cover a large area in real practice. In essence, a real-time seismic monitoring system consists of:(1) sensors deployed in the field, (2) telemetry, (3) a central receiving station where real-time data acquisitionand processing are performed, and (4) if an potential damaging earthquake has been detected, then results arecommunicated via one or more communication channels to users. For an earthquake early-warning system basedon real-time seismic monitoring, we must achieve a response time that users can take actions before strongshaking arrives. Tracking earthquake movements using GPS is just one more use for the amazing technologythat has become ubiquitous in the 21
st
century. Recently NASA is using GPS technology to find and respond tothe earthquakes. Generally, earthquake detection is done by seismological hardware on the ground, butaccording NASA
–
that data can be difficult to capture. NASA‘s answer to that problem is to use the GPS
satellites in orbit along with GPS hardware on the ground in a new network called the Real-Time EarthquakeAnalysis for Disaster Mitigation Network. The system is called READI. The READI Mitigation Network willuse real-time GPS measurements to calculate the characteristics of large earthquakes to aid early warning anddisaster relief efforts. These systems allow earthquake parameters to be broadcasted to users in a few minutesafter the earthquake occurred.