Seminário de Geofísica II (dia 6 de Abril às 14H30) do doutoramento em Ciências da Terra e do Espaço
João Fontiela, researcher
Seismology is a science dedicated to studying the inner earth and shallow processes, like seismicity at seismogenic faults, seismic hazard and risk, and volcanology, amongst many others. Nonetheless, new approaches have been used to study environmental phenomena using data recorded by seismic stations in the last years. This new field of research on seismology is environmental seismology.
Nowadays, seismicity is paramount in studying the earth, mitigating earthquake effects, and supporting other research fields like cryosphere, biology, and geography through the environmental seismology branch. During the presentation, I will show how seismology is helpful to study a volcanic region like the Azores and how human activity affects the earth humming in Portugal. The geodynamic framework in the Azores’ is uncommon due to the location in the triple junction of the American, Euro-Asian, and Nubian lithospheric. Tectonic and volcanic processes interact, increasing the seismic and volcanic hazard. The description of earthquakes’ effects started after the settlement of the Azores Islands in the 15th century. Since then, 34 earthquakes of intensity ≥ VII, and the death toll is > 6.000. The maximum observable intensity (MOI) map is an instrument to assess the seismic hazard of the historical and instrumental seismicity. Moreover, instrumental seismicity is constrained in clusters in space and time. We use the frequency magnitude distribution power law to analyze these clusters in the span of 2000 to 2012. Since the seismicity on those clusters has similar frequency magnitude distribution and focal mechanism, it allowed the discrimination of several seismogenic zones in the Azores. The last two years were marked by the COVID-19 outbreak, characterized by high transmissibility, pathogenic, and mortality. Most developed countries closed their borders and general lockdown of the population to contain the epidemic. With such a reduction in the population’s freedom, it is essential to measure the seismic noise levels due to the decline of anthropogenic activities. Thus, Portugal is studying the subject of reducing seismic noise during the first COVID-19 lockdown. It is notorious for a substantial reduction of seismic noise in the main cities of Portugal. Nevertheless, the reduction in the small towns is less remarkable despite that, in some periods, we observed an accentuated reduction of the seismic noise levels. Used in near real-time is a powerful tool to quantify the daily activity of a city’s population.