It is found in some papers, for example ([1,2,3,4,5], and references herein), that earthquake occurrence may be preceded by a geomagnetic storm, which is one of Earth's most striking manifestations of solar wind activity. A lag time between a magnetic storm onset and an earthquake occurrence varies; it could be about 2 - 6 days [1], 12-14 days [2], 26–27 days [3], some months [5], and for very large earthquakes (M7.5+) it may reach up to some years [4]. Nevertheless, the idea of a relationship between earthquake occurrence and a magnetic storm is considered up to now controversial [6]. For example, it was studied in [7] the ratio of earthquakes that happened on geomagnetically disturbed days (Dst≤ - 30 nT) to those that occurred on geomagnetically quiet days using data on 122 838 events with magnitudes from 3.0 to 7.9 that occurred from 1965 to 2005 in the Anatolian peninsula. It was concluded: “As a result of all these data, a hypothesis cannot be put forward which suggests that geomagnetic storms trigger earthquakes in the Anatolian peninsula. However, these results should not hinder the conduct of further research. A global study on this subject can potentially provide new approaches”. Our paper presents the results, which were obtained with a new, to some extent, approach. So, it was revealed in [5] that strong earthquakes prefer to occur at those longitudes after geomagnetic storms. Their high-latitudinal part was located under the polar cusp during storm onset (storm sudden commencement - SSC). From a magnetic field point of view, the polar cusp is a funnel-shaped region where the high-latitude dayside (compressed) and night side (elongated) magnetic field lines converge toward the geomagnetic poles [8]. Under the polar cusp, the solar wind plasma would directly access the Earth's environment. According to [9], most of the time, the polar cusp is between 10h and 14h of the Magnetic Local Time (MLT), but depending on solar wind and magnetosphere conditions, it may be between 08–16h [10]. In a present paper, we applied an approach [5] to investigate a possible relationship between the two catastrophic M7.8 and M7.5 Kahramanmaras earthquake sequence on February 6, 2023, with a preceded geomagnetic storm, which satisfied a condition: at the time of storm onset, the MLT in the area of the future epicenters should have been within 10h-14h [9] or 08h-16h [10]. To verify an approach once more, we analyzed, in the same way, all strong earthquakes (M≥7.0) that occurred here since 1967. The obtained results support our suggestion.

This study investigates earthquakes from the United States Geological Survey (USGS) global seismological catalog(https://earthquake.usgs.gov/earthquakes/search/). The data on the solar wind parameters are taken from the OMNI database (http://cdaweb.gsfc.nasa.gov), which was obtained from current and past space missions and projects. From the World Data Center for Geomagnetism, Kyoto (https://wdc.kugi.kyoto-u.ac.jp/), the onset and intensity of the geomagnetic storms were revealed using the 1-hour Dst (Disturbance Storm Time Index) before 1981, while the 1-min SYM-H index after 1981, since the last one is absent before 1981. The SYM-H index is, in fact, the high-resolution Dst index [11], allowing one to determine the onset and intensity of a magnetic storm correctly. According to [12], depending on the Dst value, geomagnetic storms are classified into weak (Dst from −30 to −50 nT), moderate (Dst from −50 to −100 nT), strong (Dst from −100 to −200 nT), powerful (Dst from −200 to −350 nT) and extreme (Dst below −350 nT). Also, we used data on the storm sudden commencement - SSC, which were obtained by the Observatorio del Ebro, Roquetes, Spain, from the web page (ftp://ftp.ngdc.noaa.gov/STP/SOLARDATA/sudden commencements/storm2.SSC). Since we have revealed [5] that the occurrence of strong earthquake may follow a particular magnetic storm in only a specific longitudinal region (depending on the time of geomagnetic storm onset), and since the time delay between storm onset and earthquake occurrence may enormously vary, at this step, a method of investigation was a manual. For each selected earthquake, the closest preceding geomagnetic storm was identified, which satisfied the condition: at the time of storm onset, the Magnetic Local Time (MLT) around the future epicenter should have been within 08h-16h. The MLT values were estimated using the online program (https://omniweb.gsfc.nasa.gov/vitmo/cgm.html).

One of the still open questions to the Earth and space community is how the energy of the geospace environment impacts the lithospheric processes. Some papers show that the solar flare X-ray radiation, coronal mass ejections, and geomagnetic storms may precede the occurrence of earthquakes ([1,2,3,4,5,13,14,15,16,17], and references herein). Many years of statistical searching in this direction led to a mathematical model [18] that considers a hypothesis of electromagnetic earthquakes being triggered by a sharp rise of telluric currents in the lithosphere, including crust faults, due to the interaction of solar flare X-ray radiation with the ionosphere–atmosphere–lithosphere system. A critical point in the model [18] is the increase in the ionosphere's radiation and conductivity. Besides this, it is believed that global seismic activity tends to increase in a solar minimum (e.g., [14,15,16,17], and references herein). Again, a critical point in this effect may be an increase in radiation and conductivity of the upper troposphere and lower stratosphere, produced by the galactic cosmic rays [19,20], whose intensity increases in solar minimums. It has been found recently [17] that strong earthquakes may look as addressed (targeted) because they occur near the footprints of certain geomagnetic lines belonging to a newly created radiation belt into the lower magnetosphere when the high-energy electrons in the outer radiation belt spill down due to geomagnetic storm. Again, a critical point for this effect may be an increase in radiation and conductivity in the mesosphere and upper stratosphere due to the precipitation of energetic electrons from the radiation belt up to the stratopause, as shown in [21]. Considering the above, it seems that active space weather can provoke strong earthquakes in those longitudinal regions above which a near-space environment, including geomagnetic lines, can be sufficiently populated with charged particles (be conductive). At the globe, there are two places where geomagnetic lines may constantly be filling with charged particles. These are the polar cusps where the solar wind plasma would directly access the inner magnetosphere and upper atmosphere [8,9,10]. The length of the polar cusps in longitude is determined by the Magnetic Local Time and is within the range of 10h-14h [9] or 8h-16h [10]. Due to the Earth's rotation, different longitudinal regions are located under the polar cusps during the arrival of the shocked solar wind flows. In the present paper, we considered nine strong (M≥7.0) earthquakes in Turkey, including the M7.8 and M7.5 Kahramanmaras earthquake sequence on February 6, 2023. For each earthquake, we identified a preceding geomagnetic storm that met a given criterion: a magnetic local time (MLT) at an area of a future epicenter was between 08h-16h in a time of geomagnetic storm onset. The results showed (Table 1) that before four earthquakes (M7.8 and M7.5 on February 6 of 2023, M7.3 on November 24 of 1976, and M7.3 on July 22 of 1967) there was only one geomagnetic storm with a given criterion (strong, moderate, and extreme, respectively); before three earthquakes (M7.2 on November 12 of 1999, M7.6 on August 17 of 1999, and M7.3 on March 28 of 1970) there were two magnetic storms with a given criterion (strong + powerful, strong + small, and small + small, respectively). Before one seismic event (M7.1 on October 23 2011), there were three consecutive magnetic storms with a given criterion (moderate, small, and strong). Interestingly, the 2011 year belongs to the 24 solar cycle, whose amplitude was very small. The lag time between a magnetic storm onset and earthquake occurrence varied from ~1.5 days (two cases after a series of consecutive magnetic storms) to 123 days (one case for the M7.6 Kocaeli earthquake on August 17 1999). However, on average, it is equal to ~ 49 days. It is expected to suggest that the response of seismicity to geomagnetic storms could be instantaneous if electric and electromagnetic fields interact with rocks and faults in the Earth’s crust under critical stress-strain conditions. Nevertheless, observed long lag times may tell us that the space weather phenomena do not trigger earthquakes immediately. However, they somehow deliver solar wind energy into the lithosphere, which some weeks or months later is realized in a kind of earthquake. Thus, further investigations in this area are desirable, including a retrospective analysis of the solid earth parameters in epicenter areas that were considered epicenters just after the preceding geomagnetic storms.