Seismic noise analysis during the COVID-19 lockdown

Seismic noise analysis in the Royal Observatory of Madrid

The analysis of the seismic noise recorded by the National Geographic Institute accelerometer installed in the Royal Observatory of Madrid, in the southwest area of the Retiro Park, near Atocha station, provides in an accurate way a knowledge of the anthropic activities in Madrid. This cultural noise is strongly related to human activity and not to natural causes, so its analysis is a scientific way to better understand the degree in which the decreed lockdown and de-escalation rules have been respected.

 

 

Seismic noise analysis in the accelerometric network of Spain

The accelerometric network of the National Seismic Network is located within urban centers distributed in the regions with the highest seismic activity in Spain. The objective of these seismic stations is to record the strong ground motions generated by earthquakes. Indeed, due to their locations within settled areas, these stations record a large level of cultural or anthropic noise and are sensitive to ground vibration variations generated by changes in human activities in the close environment.

By analyzing the average daily level of seismic noise in each station, it is possible to observe the effects of the decreasing and cessation of activities, as well as its resumption and the beginning of the easing measures during the different phases of the COVID-19 lockdown and during the progressive return to the ‘new normality’, following the ‘Transition Plan’ approved by the Government on April 28th.

Thus, during the spring of 2020, the average daily noise level dropped several decibels (between 1 and 5 dB, depending on the station) below the pre-lockdown reference level. During the transition phases, it progressively increased until reaching values close to and, in some cases, comparable to the reference ones. In the ‘new normality’, the noise level has remained generally constant, with a tendency to decrease slightly and, in some cases, with a very evident progressive weekly decrease, reaching values equivalent to those during the lockdown, as occurs in the accelerometer of Torre Pacheco (Murcia).

To consult the analysis of seismic noise in the Spanish seismometer network, click here