Using a dense seismic array to track the evolution of the COVID19 lockdown within Barcelona (Spain).

Abstract:

Connecting students with seismology is challenging in countries not affected by strong earthquakes. In order to mitigate this problem, the SANIMS research project included the deployment of 15 seismometers within the city of Barcelona, mostly located in secondary schools. The objective was to acquire new valuable scientific data, but also to introduce the students to Earth Science research. The network has been deployed in September 2019 and 50% of the sites have been instrumented using the low-cost RaspberryShake devices, which provide online access to the data in real time, facilitating the implication of the students.

As a result, the city of Barcelona has been covered during the COVID19 lockdown period by a relatively dense seismic network consisting of up to 20 seismic sensors, including the 15 short period SANIMS sensors, one permanent broadband station and 4 accelerometers of the ICGC network. This recorded data reveals in detail the seismic noise variations associated to human activity. As reported in other places, the amplitude reduction is in the order of 30-50% and concentrated in the 1-15 Hz band, proving that human activity dominates this band. The data for the permanent broad-band station have been analyzed since June 2019, proving that the reduction during lockdown is significantly larger than during summer holidays.

The general picture is consistent between all the sites. However, as noise is dominated by sources located near the sensors, significant differences on the details of the noise level evolution between sites can be observed. A couple of sites hardly show a noise decrease during lockdown, in a couple more of locations the decrease is restricted to the 2 weeks of total lockdown, while in most of the sites the variation of the noise level is more gradual. Hereof, caution must be taken before taking the results from a single sensor as representative of large and populated areas. Analyzing the time evolution of the seismic noise on the network provides a picture of both the general degree of activity within Barcelona and of the specific characteristics of each zone. Beside the scientific interest of the recorded data, this exceptional situation has provided an excellent opportunity to reach a public not usually familiar with Earth sciences.

This is a contribution of the SANIMS project (RTI2018-095594-B-I00)