Maximum Magnitude of Earthquakes in the Yerevan Fault Zone May Reach 6

In recent days, nature has been reminding us that we live in a seismically hazardous region. The Institute of Geological Sciences of the National Academy of Sciences has released this information. The message states: “In the last few days, two moderate earthquakes were registered in the territory of Armenia, the first one in the vicinity of the Sevan mountain range, in Shorja (on February 5, according to the data from the RA MES Seismic Protection Territorial Service, M=4.7), the other near the city of Masis on February 13 (according to preliminary data from the RA MES STS, M=4.7). The last earthquake, which had an epicenter closer to Yerevan, caused significant tremors and alarmed the residents.

These earthquakes are related to two different seismically active faults associated with different tectonic structures. The earthquake on February 5 was linked to Armenia's longest active fault, the Pambak-Sevan-Syunik fault, while the earthquake on February 13 was associated with the Yerevan deep fault. These two seismically active structures are included in the seismic tectonic model of the territory of Armenia, developed by the Institute of Geological Sciences based on years of research on active faults in Armenia. This seismic tectonic model forms the basis of the probabilistic assessment map of seismic hazards in Armenia, which was developed within the framework of international cooperation and approved by the Government of the Republic of Armenia in 2018.

Based on this data, a seismic diversion map of the territory of Armenia was compiled and officially approved in 2020. According to the seismic tectonic model, the maximum magnitude of earthquakes in the Yerevan fault zone may reach 6.0. The seismic hazard of the Pambak-Sevan-Syunik active fault is significantly higher, potentially causing much stronger earthquakes, up to M=7.5. For comparison, the magnitude of the Spitak earthquake was M=6.9.

It is also important to note that, worldwide, there are 9-25 earthquakes of magnitude M=7-7.9 every year, 120-180 earthquakes of magnitude M=6-6.9, and the number of earthquakes of magnitude M=5-5.9 exceeds tens of thousands annually. In Armenia, more than 300 earthquakes occur each year, most of which do not exceed a magnitude of 2 and are often not felt by the population.

On February 5 and 13, 2021, the epicenters of the registered earthquakes are shown on a schematic tectonic map. It is also crucial to note that after the main shock of the Shorja earthquake, numerous aftershocks of lower magnitude were recorded. A similar pattern was observed after the Yerevan earthquake on February 13, which is a normal sequence of events following an earthquake of this magnitude, as it denotes the release of stress in the focal zone.

Historically, earthquakes have occurred around the city of Yerevan that have not only been felt in Yerevan but have also affected its buildings and structures. This focal zone is known for its activity. The first recorded earthquake in the Parakar (Yerevan) area occurred on January 25, 1910, with a magnitude of M=4.5, felt with an intensity of 6-7 points in Yerevan. The most notable earthquake in this area occurred on January 25, 1937, with a magnitude of M=4.8 and I=7.0, which caused partial destruction of buildings in the Parakar and Argavand villages.

Significant earthquakes have also been recorded in this focal zone on June 16, 1973 (M=4.0, I=5-6), February 25, 1978 (M=4.0, I=5-6), August 2, 1984 (M=4.0, I=5-6), August 9, 1994 (M=3.0, I=4-5), March 1, 1997 (M=3.7, I=5-6), July 29, 2005 (M=3.0, I=4-5), April 11, 2007 (M=3.0, I=4-5), and November 4, 2008 (M=3.2, I=4-5).

The potential of the Yerevan fault is relatively low. This fault is characterized by weak and moderate earthquakes occurring with considerable frequency. According to statistical data for earthquakes occurring during the instrumental period, the frequency of earthquakes with M>3.0 in this focal zone is approximately every 4-5 years.

The scientific network of seismic observations of the Institute of Geological Sciences of the National Academy of Sciences has recorded these earthquakes, and in the near future, more detailed scientific investigations of the significant tremors and aftershocks will be conducted, and the obtained data will be published in scientific journals. A similar study dedicated to the September 10, 2019, Bavra earthquake of M=4.8 was published in the 3rd issue of the 2020 report on Earth Sciences by the National Academy of Sciences of Armenia.