Compensatory movements in the source zone of the 2023 high-magnitude earthquake swarm in Herat province, Afghanistan

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Abstract

A source of a strong earthquake, as a rule, consists of subsources which are identified by waveform modeling. The modeling does not yield an unambiguous result. In this paper, we present an example when two significantly different focal mechanism solutions are published for the same earthquake: in one solution, the subsources are characterized by a similar type of faulting, while in the other solution, the last subsource has an opposite mechanism. In (Vakarchuk et al., 2013), this discrepancy was interpreted by the realization of a compensatory motion. The compensatory movements are detected not only in the subsources but also at the scale level of the entire source zone, which manifest itself in a certain regularity of the aftershock mechanisms discovered in the study of the 1970 Dagestan earthquake by Kuznetsova et al. (1976). In this paper, perhaps for the first time, compensatory movements are detected in a high-magnitude earthquake swarm without a pronounced main shock, which occurred in 2023 in Herat Province, Afghanistan. The results are supported by a series of seismological and satellite interferometric data.

About the authors

R. E. Tatevossian

Schmidt Institute of Physics of the Earth, Russian Academy of Sciences

Author for correspondence.
Email: ruben@ifz.ru
Russian Federation, Moscow, 123242

A. V. Ponomarev

Schmidt Institute of Physics of the Earth, Russian Academy of Sciences

Email: ruben@ifz.ru
Russian Federation, Moscow, 123242

E. P. Timoshkina

Schmidt Institute of Physics of the Earth, Russian Academy of Sciences

Email: ruben@ifz.ru
Russian Federation, Moscow, 123242

Zh. Ya. Aptekman

Schmidt Institute of Physics of the Earth, Russian Academy of Sciences

Email: ruben@ifz.ru
Russian Federation, Moscow, 123242

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Supplementary files

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2. Fig. 1. (a) – The mechanism of the earthquake of 06/08/1993 (red), preceding (gray) and subsequent earthquakes within six months (black) (Global CMT catalog. URL: http://www.globalcmt.org. The last download was in 2023); (b) – the earthquake of 05.12.1997. The legend is similar to (a).

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3. Fig. 2. The mechanism of the earthquake of 15.01.2009 (red) and its strongest aftershock within six months (Global CMT catalog. URL: http://www.globalcmt.org. The last download was in 2023).

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4. Fig. 3. Seismotectonic framing of the earthquake area. The frame shows the epicentral region of the swarm. The gray arrows indicate the direction of immersion of the relict subduction zones. Active faults according to [Bachmanov et al., 2017] are shown by red lines.

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5. Fig. 4. Mechanisms of strong earthquake foci (Mw ≥ 7.0) according to the Global CMT source (1976-2023) (Global CMT catalog. URL: http://www.globalcmt.org. The last download was in 2023). The mechanisms of earthquakes in the Pamir – Hindu Kush zone with a hypocenter depth of 70 km or more are painted in black. The dotted line shows the area presented in detail in Fig. 5. Active faults according to [Bachmanov et al., 2017] are shown by red lines.

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6. Fig. 5. Mechanisms of earthquake foci (Mw ≥ 6.0) (Global CMT catalog. URL: http://www.globalcmt.org. The last download was in 2023). The mechanisms of earthquakes with a hypocenter depth of 70 km or more are painted in black. The mechanisms of the Herat earthquakes are highlighted in red. The circle shows the area shown in detail in Fig. 6. Active faults according to [Bachmanov et al., 2017] are shown by red lines.

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7. Fig. 6. Mechanisms of earthquake foci (Mw ≥ 6.0) according to the Global CMT source (Global CMT catalog. URL: http://www.globalcmt.org. Last downloaded in 2023) in the vicinity of the Herat earthquakes. The mechanisms of the Herat earthquakes are highlighted in red. Earthquake numbers correspond to the table. Active faults according to [Bachmanov et al., 2017] are shown by red lines.

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8. Рис. 7. Фазовая неразвернутая интерферограмма для двух землетрясений 07.10.2023 г. Красные звезды показывают положение эпицентров землетрясений с магнитудой 6.3 (первое по времени событие произошло севернее второго).

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9. Fig. 8. (a) – The field of displacements of the Earth's surface in the direction of the satellite in meters on the Google Earth Pro map. Red color – offsets towards the satellite (“lifting”), blue – “lowering”; (b) – the same displacement map (starting from 50 mm) on the digital ETOPO1 relief model.

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10. Fig. 9. Phase non-inverted interferogram for two earthquakes on October 11 and 15, 2023. Each color cycle (from blue to red) corresponds to a phase shift of 2π of the radar signal reflected from the same area of the earth's surface during the first and second surveys.This is equal to a displacement of 28 mm in the direction of the satellite during the survey period.

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11. Fig. 10. The field of displacements of the earth's surface in the direction of the satellite in fractions of a meter on the Google Earth Pro map: red color – displacements towards the satellite (“raising"); blue – “lowering". The offsets are shown starting from 50 mm on the digital ETOPO1 relief model: purple stars are epicenters according to GCMT data; green ones are from the USGS website.

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