Yesterday the local quarry blasted some rock and we captured the seismic and infrasound signals from the blast.
In the past we have detected cross channel stimulation where a strong seismic arrival creates local infrasound, and where strong infrasound creates a local seismic signal. For example it’s not unusual for the infrasound from a passing helicopter to be detectable on the EHZ channel of a Shake.
Below is a report we specifically produced to study these interactions between the EHZ and HDF channels on Raspberry Shakes and Booms. This is from yesterday’s blast.
Looking at the top 2 plots for Station R21C0, we can see no significant local infrasound from the seismic arrival, but we can see a local seismic signal from the infrasound arrival.
The next 2 plots are for station R5968, which is a bit further away. In this case there’s no significant local cross stimulation either way.
The bottom 3 plots are for RS3D station R4FA0 which is installed in a vault approximately 100m from R21C0. Notice there is no local seismic signal corresponding to the infrasound arrival. This is the first time R4FA0 has been in the vault when the local quarry blasted.
R21C0 is currently installed in a large shed with concrete floor, steel frame and clad with colorbond corrugated iron. The shed is 10m x 12m with 3.9m eaves and 5.9m peak.
R5968 is currently installed in a smaller shed, roughly 3m x 3m and 2.4m tall.
While both shed size and distance from the blast may account for the lack of infrasound to seismic cross over at station R5968, the distance from the blast to stations R21C0 and R4FA0 is essentially the same, so only shed size is a factor in the amount of infrasound to seismic cross over.
This suggests that for the cleanest seismic signals (i.e. minimum infrasound to seismic cross over), the smaller the structure the Raspberry Shake is installed in the better. The shed or structure basically acts as an infrasound to seismic transducer (and likely vice versa).