Pattern analysis of seismicity around Mavrovo lake: a case study for the period July 2020 - November 2021

Two moderate earthquakes with magnitude M_L5.0 happened on the 11^th of November 2020 near the Mavrovo lake in northwestern Macedonia. Mavrovo lake is an artificial lake with a dam built between 1947 and filled by 1953. Its maximum length is 10km, width is 5km and depth is 50m. We try to investigate the factors which might be causing earthquakes, for example, local geology and seismotectonic regime in the region.

Seismic events of such size can have various sequences of foreshocks and aftershocks, which mostly depend on the earthquake mechanism. In this case study, a numerical analysis was done for the first time from the list of events reported by the Skopje Seismological observatory, that occurred some six months prior to the main events and one year after, till November 2021.

 

A list of 180 earthquakes registered by the local and regional stations with magnitudes equal or greater than M_L1.7 was analyzed in more detail in terms of temporal and spatial distribution around the lake, in a polygon area defined by geological features. No statistically significant clustering of events was noticed in the foreshock period from July 2020. In the aftershock period, the most numerous events lasted about a month after the main events. However, there was another period of increased seismicity during March 2021, followed by a gradual decrease onwards.

The preliminary distribution of epicenters was mainly along the terrain of Radika river and close monitoring continues to establish possible longer-term variations of seismicity. Comparative analysis with various periods will be also considered in order to determine any patterns of seismicity.