Blowing in the wind

Yesterday has been a windy day in Tuscany. Many trees fell down, lots of roofs were destroyed, old town walls reduced into a pile of bricks. The wind speed reached 150 km/h, an exceptional event for our region.

This unusual event left its footprint on the waveforms recorded by LA GILBERTA, especially during the night, when urban activity is very low. The sensor showed a marked increase of the seismic noise compared to an usual night when just some car passings are recorded. Let us have a look at the night of March 4th, when the Mw=3.7 Chianti earthquake occurred. The picture below shows the SEP seismogram (high pass filtered with a frequency of 1 Hz) from 1 a.m. to 6 a.m. local time. Except for the earthquake at midnight, it was a quiet night in Via della Faggiola, where the station is operating.

But what about yesterday night? The wind signatures are very strong in the seismogram! Our record shows two hours  of sustained activity from 2.15 to 4.15 local time. If you are curious about waveforms of ground movement due to different sources, a good summary can be found in this document by IRIS/USGS.