The time required to detect and issue a warning for an earthquake is dependent on several factors:
- Distance between the earthquake source and the closest station. It takes a finite amount of time for seismic waves to travel from the source (e.g. the point on a fault that is breaking) to the seismic station. The first waves to arrive at a station are the lower amplitude P waves that travel at 5-6 km/s, on average. The large amplitude (more damaging) S waves travel at ~3 km/s. Therefore, the closer a station is to the fault, the more rapidly the earthquake can be detected. Accurate detections often depend on multiple ground motion measurements from more than one station; so, increasing the density of stations near the fault can improve detection times.
- Transfer of information to the regional networks. Data from multiple must be collected and analyzed at the regional seismic networks, so ground motion information must be transferred from the station to the central network. The CISN and PNSN use a variety of methods to send data back to the server to improve robustness, including radio links, phone lines, public/private internet, and satellite links. In addition, delays with packaging and sending the data from the station must be reduced. Recent upgrades to the CISN and PNSN have been completed to reduce latencies in packaging and sending ground motion observations useful for ShakeAlert.
- Detection and characterization of an earthquake. Ground motion records received from the stations in real time are used to detect if an earthquake is occurring and rapidly determine the location and magnitude of the event. We are developing multiple algorithms to estimate the earthquake information as rapidly as possible.