Improved detection capability of array beamforming
The concept of placing many seismic sensors in a certain geometry is known as seismic arrays. Due to different distances between individual sensors, optimized constructive stacking of the signal while taking advantage of destructive interference of the noise increases the signal-to-noise ratio significantly compared to single station observations. This allows for a significant increase in the event detection capabilities. In addition, seismic arrays provide information on the direction and velocity of the approaching signal, which allows to discriminate real events from noise, and to improve event locations, especially for events with only a few station observations.
The Figure below demonstrates the signal-to-noise improvement through array beamforming as applied to a small magnitude 1 earthquake recorded by the HNAR array at Holsnøy compared with nearby single seismic stations.
Figure: The above picture shows recorded seismic movements origination from a magnitude 1 microearthquake (location shown as small yellow dot in the map). The black traces correspond to single stations in Western Norway (black triangles) and the red traces belong to the seismic array HNAR. The microearthquake is not observed on most single stations, only on the closest station, SUE, some energy is visible. The individual sensors of the array, although further away, also indicate energy originating from the microearthquake. The two green traces then show the results of array beamforming where P- and S-wave onset readings can be conducted. The process also provides the direction of the event and the wave velocity.