In real-time monitoring, signals from seismic sensors in the field (either analog or digital) are telemetered to a central receiving station for processing. By real-time we mean that the results can be obtained within seconds or tens of seconds. In practice, there are several obstacles to achieving a quicker response. Large earthquakes 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 in Hualien, 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 not economical 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 acquisition and processing are performed, and (4) if an potential damaging earthquake has been detected, then results are communicated via one or more communication channels to users. For an earthquake early-warning system based on real-time seismic monitoring, we must achieve a response time that users can take actions before strong shaking arrives. Tracking earthquake movements using GPS is just one more use for the amazing technology that has become ubiquitous in the 21
st
century. Recently NASA is using GPS technology to find and respond to the earthquakes. Generally, earthquake detection is done by seismological hardware on the ground, but according NASA
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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 Earthquake Analysis for Disaster Mitigation Network. The system is called READI. The READI Mitigation Network will use real-time GPS measurements to calculate the characteristics of large earthquakes to aid early warning and disaster relief efforts. These systems allow earthquake parameters to be broadcasted to users in a few minutes after the earthquake occurred.