Time delay detector in seismic signals using real-time multipoint radiofrequency links

Seismic waves are composed of a superposition of waves that differ in their frequencies, speed of propagation, and amplitude. In particular, primary seismic waves (P waves) travel faster than secondary seismic waves (S waves), which are more destructive. This property allows P waves to be detected first than the S waves, giving a chance to activate an alarm if considered so. This work presents a prototype to monitor the P waves of an earthquake at different geographical points. A radio communication link between a few locations is established, and the seismometers consist of Lehman pendulums. The signals from the seismographs are Fourier-transformed continuously and cross-correlated to discern between the presence of a seismic signal or noise. The system developed consisted of real-time multipoint communication in the UHF band. Three nodes were implemented to evaluate its performance. These consisted of two distant points transmitting data from seismic sensors, and a receiver located in the central node read those signals. This point also had its detector and performed signal processing and information visualization through a graphical interface. Experimentally, the multipoint communication permitted the continuous transmission of information between the different nodes in real-time, using test signals with programmed time delays, which agreed with those calculated by the algorithms, with an accuracy of tenths of milliseconds.