On Problems of Detecting Blasts in Earthquake Catalogs: Case Study of Turkey and Iran

Catalogs of weak seismic events (M ≤ 4) in Turkey and Iran were analyzed to identify signs of their contamination with blasts. A well-pronounced predominance of the number of seismic events and a decrease in their average magnitude in the period from 10:00 to 17:00 LT were found. The epicenters of seismic events that occurred in this time interval at depths of less than 3 km are located much more compactly than other seismic events. Such indications can be considered as an evidence of contamination of the earthquake catalogs with road, mine, and quarry blasts. The presence of such an anthropogenic effect in the earthquake catalogs is also confirmed by the presence of a well-defined weekly periodicity of seismic events. It manifests in the form of a significant weakening of the discussed daytime extremum on Saturday and Sunday in Turkey and on Friday in Iran. Using the example of Turkey, where the observation service attempted to separate blasts and earthquakes in the seismic catalog, it is shown that in an earthquake catalog, which was purified this way, the prevalence of seismic events in the daytime over their number in the nighttime is still observed. The opposite effect was also revealed, namely, the presence of earthquakes in the blast catalog; i.e., there is a mutual contamination of the catalogs of earthquakes and blasts. However, it cannot be excluded that the relative increase in the number of earthquakes in the daytime is only partially caused by the presence of undetected explosions due to imperfect algorithms for discriminating between blasts and earthquakes. The daytime extremum in the number of earthquakes can be partially generated by the occurrence of additional weak earthquakes triggered by relatively strong blasts (i.e., by the triggering effect of explosions on the natural process of seismogenesis). The obtained results show that even in case of earthquake catalogs that are claimed to be cleared of blasts, it is necessary to carry out preliminary study these catalogs in order to assess their contamination with blasts.