Regional Seismic Stations Research Articles

SEISMICITY of the BAIKAL REGION and TRANSBAIKALIA in 2020

We consider a character of the seismic process in the Baikal region and Transbaikalia in 2020. A total number of registered earthquakes with KR≥5.6 was 7711. Most of them (94 %) occurred in the Baikal rift zone where the South Baikal and Baikal-Muya regions were the most active (by number of earthquakes). The strongest seismic events – the September 21, 2020 Bystraya (Mw=5.6) and December 9, 2020 Kudara (Mw=5.5) earthquakes – were localized in the Hovsogol-Tunka and South Baikal regions respectively. Both events in the near-field zone (∆≤19 km) were felt with an intensity of 6–7. Noticeable macroseismic effects with less intensity were observed from another 34 earthquakes with KR≥8.4. Focal mechanisms were determined for 77 earthquakes (KR≥9.1) using two methods: from P-wave first-arrival polarities on regional seismic stations and during calcula tions of a seismic moment tensor (in a double-couple approximation) based on surface wave amplitude spectra. It has been shown that normal fault movements, which are often combined with strike-slips, are dominated in sources of regional earthquakes. In general, the region is characterized by moderate seismic activity in 2020, total seismic energy is estimated as 573∙1012 J that is two times higher than the same parameter calculated in 2018–2019.

SPECTRAL and FOCAL PARAMETERS of CRIMEAN-BLACK SEA REGION EARTHQUAKES in 2020

The results of calculation and analysis of spectral and focal parameters of 11 earthquakes in the Crimean-Black Sea region in 2020 within the range of energy classes Кп=5.2–11.3 are presented. The dynamic parameters of the sources were reconstructed from 70 amplitude spectra of P- and S- seismic wave records rec orded by eight digital regional seismic stations. For the two strongest earthquakes of 2020: March 15 and April 12, the focal mechanism solutions were obtained. The type of slip in the sources of both earthquakes is a reverse fault. In addition, the spectral properties of the sources of 10 weak earthquakes that occurred near the southern coast of Crimea were considered from the energy spectra of records at the Alushta station. An analysis of the results obtained is given.

The 2020 Mw 6.6 Vernadsky transform earthquake sequence: rupture and Coulomb stress changes surrounding an oceanic core complex

Oceanic core complexes (OCCs) are upwards-convex areas of outcropping lower crustal or upper mantle rocks raised to the seabed by normal faults, commonly associated with weak lithologies such as serpentinites. They are common adjacent to transform valleys of slow-spreading ridges. In this paper, we analyse the September 2020, Mw 6.6 strike-slip earthquake and its two-week long aftershock sequence within the Vernadsky transform valley, using recordings from regional seismic stations. The aftershocks occurred in two phases. During the first four days, ∼ 131 events occurred east and northeast of the mainshock, overlapping an adjacent OCC complex along the northern flank of the transform valley. During the following nine days, 20 aftershocks occurred, including a Mw 5.8 event close to the OCC. To refine the locations of aftershocks, the spatial spread of the events (clustering) was refined by double-difference relocating 114 events, and five with teleseismic relative relocation. Modeling of static Coulomb stresses was carried out, based on a mainshock rupture length compatible with the 26–30 km horizontal extent of aftershocks. This revealed that the aftershocks occurred mainly in areas where static Coulomb stresses decreased, not increased. Other researchers have suggested that changes in fault strength can arise from dynamic stresses during major earthquakes, leading to seismicity in areas of decreased Coulomb stress. We explore this idea in the context of OCCs.

Coda-derived source properties estimated using local earthquakes in the Sea of Marmara, Türkiye

Abstract. Accurate estimates of the moment magnitude of earthquakes that physically measure the earthquake source energy are crucial for improving our understanding of seismic hazard in regions prone to tectonic activity. To address this demand, a method involving coda wave modelling was employed to estimate the moment magnitudes of earthquakes in the Sea of Marmara, northwestern Türkiye. This approach enabled us to model the source displacement spectrum of 303 local earthquakes efficiently recorded at 49 regional seismic stations between 2018 and 2020 in the region. The coda wave traces of individual events were inverted across 12 frequency ranges between 0.3 and 16 Hz. The resultant coda-derived moment magnitudes were found to be in good accordance with the conventional local magnitude estimates. However, the notable move-out between local magnitude and coda-derived moment magnitude estimates for smaller earthquakes less than a magnitude of 3.5 likely occurs due to potential biases arising from incorrect assumptions for anelastic attenuation and/or the finite sampling intervals of seismic recordings. Scaling relations between the total radiated energy and seismic moment imply a non-self-similar behaviour for the earthquakes in the Sea of Marmara. Our findings suggest that larger earthquakes in the study area exhibit distinct rupture dynamics compared to smaller ones, resulting in a more efficient release of seismic energy. Hence, we introduce an empirical relationship obtained from the scatter between local magnitude and coda-derived moment magnitude estimates.

Forensic Seismic Evidence for Precursory Mobilization in Gaza Leading to the October 7 Hamas Attack

Abstract This study analyzes the seismic noise wavefield recorded before the October 7 Hamas attack on Israel. Preattack activity involved large-scale mobilization, as was documented by various media sources. Opportune conditions stemming from a temporary reduction in Israeli anthropogenic activity enabled the identification of signals generated by vehicular movement in Gaza at three regional seismic stations. Seismogram analysis reveals a widespread signal that abruptly emerged above the nighttime noise levels about 20 min before the attack began. Previous Saturday mornings did not exhibit interstation correlations and signal amplitudes as high as the ones observed on the three stations in the minutes before the attack began. Statistical analysis suggests the October 7 preattack signal is highly anomalous and unlikely to emerge by chance. Tripartite array analysis was used to detect surface waves, locate their sources, and demarcate the extent of preattack activity within the Gaza Strip. The signal’s amplitude, frequency, and spatiotemporal distribution appear to be aligned with vehicular traffic emanating from the south-central region of the Gaza Strip and extending toward its peripheries in the half-hour window preceding the invasion. This analysis underscores the potential utility of seismic noise measurements in identifying large-scale terrorist vehicular mobilizations in advance.

The September 6, 2021 MW 5.4 Tofalaria earthquake at a weakly active segment of the Main Sayan fault (Eastern Siberia)

We study in detail the Mw 5.4 September 6, 2021 Tofalaria earthquake occurred in a mountain area of the Eastern Sayan which is characterized by a low level of seismic activity. An interest in the seismic event is caused, on the one hand, by poor knowledge about stress-strain field of the crust in the considered region, and, on the other hand, by its relation to the NW segment of the ancient Main Sayan fault – a structural boundary between the Sayan-Baikal fold belt and the tectonically stable Siberian platform. Seismic moment tensors and hypocentral depths of the mainshock and its largest aftershock (Mw 4.6) are inverted from intermediate-period surface wave amplitude spectra calculated at the stations located at teleseismic distances. Integral source parameters of the mainshock, characterizing its spatio-temporal development, are also estimated and the fault plane is determined. Epicenters of 31 aftershocks with M ≥ 1.8, occurred up to the end of 2021, are constrained from body waves recorded at regional seismic stations. The obtained results show that the Tofalaria earthquake occurred under the influence of the SW-NE compression, which is observed in Western Mongolia. Focal mechanism of the largest aftershock and the NE elongation of the aftershock epicentral field (22 km) indicate stress redistribution after the mainshock in a local crustal volume, bordered by small-scale faults.

Earthquake on January 24, 2024 near Krasnodar city, Mw=4.1, I0=5

The article presents instrumental and macroseismic data on the earthquake on January 24, 2024 at 11:19 (UTC), Mw=4.1, h=8 km. The earthquake parameters were determined using instrumental data from the network of regional seismic stations in the North Caucasus of the GS RAS. The earthquake parameters were determined from instrumental data from the network of regional seismic stations in the North Caucasus of the GS RAS. The source spectra of three regional seismic stations (GOYR, MRNR and GUZR) were calculated, from which the seismic moment М0, the stress drop Δσ and the source radius R were determined. The solution of the focal mechanism was obtained from the polarization in P-waves at 71 seismic stations and the type of source fault with a right-lateral strike-slip component. The epicentral zone of the earthquake on 24.01.2024 is located within the high-magnitude Akhtyrka zone of potential earthquake source zones (ESZ) with Mmax=6.5-6.8 and represents the boundary between the Northwestern part of the structures of the Greater Caucasus and the West Kuban trough. According to macroseismic survey in the regions, 300 respondents were interviewed in 20 settlements. The maximum observed intensity was I=V MSK-64.

Source types of induced earthquakes in underground mines: Revealed by regional moment tensor inversion

Mining-induced earthquakes have been very frequent in recent years due to increasing mechanized mining. Compared with natural earthquakes, even a small one may cause significant damage to the mine area and its surroundings. Source type identification is important for better understanding the physical processes and is a crucial and fundamental issue for hazard assessment and emergency rescue in the mining environment. The moment tensor (MT) theory plays a pivotal role in distinguishing different source types. In this study, we concentrated on two strong reported “mine collapse earthquakes” in Qufu (ML 3.2, July 13, 2020) and Zoucheng (ML2.9, June 09, 2020), Shandong Province, China. Seismograms from regional seismic stations were utilized to calculate the full moment tensors through low-frequency full-waveform inversion. Our results show that the two studied events exhibit notably different source types. The DC (Double-Couple) component of both events are 5% (Qufu) and 60% (Zoucheng), respectively. The Qufu event which contains approximately 75% closing crack component, is more consistent with the theoretical models of collapse seismic source. However, the Zoucheng event, which exhibits a significant proportion of DC components, demonstrates characteristics typical of shear failure. Focusing on the Zoucheng event, which occurred at the Dongtan Coal Mine, further research was conducted on a local mining scale. Analyzed in conjunction with microseismic sensor data, geologic setting, and mining progress, we illustrated that the source type of Zoucheng event is not a collapse one. The fracture slip of a thick-hard roof due to an overlying load, characterized by a large DC component, is a plausible geomechanical interpretation.

Сейсмические события в Воркутском углепромышленном районе в 2023 году

In 2023, regional seismic stations recorded 25 seismic events in the Vorkuta coal industrial district of the Komi Republic, with a local magnitude ML from 1.8 to 2.8. A significant contribution to the detection of weak, ML ≤ 2, events was made by data obtained from the temporary seismic station of the IG FRC Komi SC UB RAS, installed as part of expeditionary work in the summer of 2023 in the Polar Urals.
 Among them the seismic event on August 1, 2023, which had a macroseismic effect, is of particular interest. Residents of several districts of Vorkuta felt tremors similar to an earthquake. Seismic records from 5 stations with epicentral distances from 40 to 1070 km were processed. The following parameters of the epicenter were obtained: t0 = 18:39:07, 67.529N, 64.001E, h = 0 km, Rminor = 3.9 km, Rmajor = 6.7 km, AzMajor = 90°, Kp = 9.0, ML = 2.8, Ms = 2.35. The instrumental epicenter of the event is located in Vorkuta, near the mine field of the Vorkuta mine. We classified the seismic event as a rock burst. Macroseismic intensity calculated in accordance with the Seismic intensity scale-2017 using 57 questionnaires and 163 definitions of sensor categories was I0 = 4.73 ± 0.02. The calculated value of the macroseismic depth of the source was H = 0.5 ± 0.4 km, which corresponds to the instrumental definition and to the range of depths of mine workings of the Vorkuta coal deposit.

Shake to the Beat: Exploring the Seismic Signals and Stadium Response of Concerts and Music Fans

Abstract Large music festivals and stadium concerts are known to produce unique vibration signals that resemble harmonic tremor, particularly at frequencies around 1–10 Hz. This study investigates the seismic signals of a Taylor Swift concert performed on 5 August 2023 (UTC) as part of a series at SoFi Stadium in Inglewood, California, with an audience of ∼70,000. Signals were recorded on regional seismic network stations located within ∼9 km of the stadium, as well as on strong-motion sensors placed near and inside the stadium prior to the concert series. We automatically identified the seismic signals from spectrograms using a Hough transform approach and characterized their start times, durations, frequency content, particle motions, radiated energy, and equivalent magnitudes. These characteristics allowed us to associate the signals with individual songs and explore the nature of the seismic source. The signal frequencies matched the song beat rates well, whereas the signal and song durations were less similar. Radiated energy was determined to be a more physically relevant measure of strength than magnitude, given the tremor-like nature of the signals. The structural response of the stadium showed nearly equal shaking intensities in the vertical and horizontal directions at frequencies that match the seismic signals recorded outside the stadium. In addition, we conducted a brief experiment to further evaluate whether the harmonic tremor signals could be generated by the speaker system and instruments, audience motions, or something else. All evidence considered, we interpret the signal source as primarily crowd motion in response to the music. The particle motions of the strongest harmonics are consistent with Rayleigh waves influenced by scattered body waves and likely reflect how the crowd is moving. Results from three other musical performances at SoFi in summer 2023 were similar, although differences in the signals may relate to the musical genre and variations in audience motions.

Comprehensive seismic evidence for the inducing mechanism of extremely shallow 2019 Changning Ms 6.0 earthquake by solution salt mining, Sichuan Basin, China

Abstract In the Changning region of the Sichuan Basin, China, which has experienced decades-long injection of freshwater for commercial salt mining, a Ms 6.0 earthquake occurred in June 2019, along with four Ms >5 aftershocks. Using data from local and regional seismic stations, we determine accurate locations for this earthquake sequence, velocity structures, and excess pore fluid pressures of the source region. Our results show that the Ms 6.0 earthquake is extremely shallow (~1.6 km below mean sea level) and is associated with low Vs and high Vp/Vs values and excess fluid pressures, indicating a fluid-induced earthquake. The mainshock was likely the shallowest M >6.0 induced earthquake, and it was triggered by the combined effect of pore pressure increase from the diffusion of injected fluids, differential formation subsidence from salt caverns, and highly fractured slip-prone rocks enriched in quartz and silica content. Following Coulomb stress transfer from the mainshock, the sequence ruptured in a cascading manner involving preexisting oblique faults of varying dips.

EARTHQUAKE SWARMS AS EVIDENCE OF VOLCANO-TECTONIC PROCESSES OF THE SLOWEST SPREADING GAKKEL RIDGE IN THE ARCTIC

Based on the data from the Arctic regional seismic stations, the article presents the results of studying the swarm seismicity of the Gakkel Mid-Ocean Ridge, located in the Arctic Ocean. The active spreading processes of ultraslow ridges with spreading rates of less than 20 mm/yr, which include the Gakkel Ridge, are still poorly understood as compared to the MOR in the Atlantic and Pacific oceans, with spreading rates of more than 25 mm/yr. In 2012–2022, there were identified eight swarms: one within the western volcanic segment of the ridge, others – in the eastern volcanic segment. No earthquake swarms were recorded in the central amagmatic segment of the ridge; the recording therein covers primarily single earthquakes and aftershock sequences. Spatially identified swarms are confied to some volcanic centers revealed earlier from the geological and geophysical data during complex expeditions. The ridge segment at coordinates ∼85…∼93° E is characterized by the most intense manifestations of volcanic processes. The spatial distribution of swarms may also indicate potential presence of volcanic structures that have not yet been identified from the geological, geophysical and geomorphological data. In the temporal domain, there can be preliminarily distinguished a 5-year swarm activation cycle, which, however, requires additional verification over a longer time interval. The swarm seismicity of the slowest spreading Gakkel Ridge cannot be described by a simple model of volcanism and magma intrusion into a symmetrical rift; it is rather a result of a complex interaction between diking and faulting with magma transport along the faults with potentially significant seismic activities. There can probably be suggested a regular combination of the processes of volcanic activation and seismotectonic destruction, which is especially pronounced in the locations of transverse faults. The results described in this article expand our understanding of the manifestation of volcano-tectonic processes occurring within the slowest speading Gakkel Mid-Ocean Ridge.

Erratum to An Evaluation of the Timing Accuracy of Global and Regional Seismic Stations and Networks

<i>Erratum to</i> An Evaluation of the Timing Accuracy of Global and Regional Seismic Stations and Networks

Time-Varying Moment-Tensor Analysis with Application to Buried Chemical Explosions

Abstract The Source Physics Experiment (SPE) Phase I consisted of a series of over-buried, horizontally colocated chemical explosions at the Nevada National Security Site. Seismic waveforms from these explosions recorded at near-source accelerometers, local geophone arrays, and regional seismic stations provided a rich suite of observations suitable for resolving fine source details. To investigate the time-varying source history of the explosions, we used the frequency-domain moment-tensor inversion method described in Yang et al. (2018) with added regularization and reconstruction to suppress the nonuniqueness evident in unconstrained inversion results. The inverted moment-rate spectra are accurate within the response band of the local geophones and, in all cases, display predominately isotropic characteristics. For SPE-4Prime, SPE-5, and SPE-6, we resolve predominately isotropic moment release followed by double couple and compensated linear vector dipole (CLVD) release later in the time-varying source history. We interpret these results both in terms of absolute depth and scaled depth of burial. The apparent non-isotropic release from SPE-4Prime and SPE-5 may simply reflect increased resolving power related to improved Earth model accuracy at greater absolute depths, whereas the non-isotropic release from SPE-6 likely reflects the larger damage associated with an event at a shallower scaled depth. These results provide insight into the time-varying source characteristics of shallow explosions and motivation to study shear-wave generation by inverting for fracture, spallation, induced slip, and other temporally delayed source processes through time-varying methods.

Shear-wave splitting patterns in Perachora (Eastern Gulf of Corinth, Greece)

The Eastern Gulf of Corinth (EGoC) is one of the most seismically active areas in Greece. It is monitored by local and regional seismic stations of the Hellenic Unified Seismic Network (HUSN). In 2020, a high-yield seismic sequence, lasting over five months, occurred at the Perachora peninsula. This provided a unique opportunity to investigate the anisotropic properties of the upper crust in the area, which lacks relevant studies. The sequence exhibited characteristics of a seismic swarm, with the strongest event having a magnitude of 3.7. In the herein analysis, we use recordings from suitable HUSN stations for two periods: (a) 2008 to 2019, a period of scarce seismicity, to identify background anisotropy and (b) the 2020 seismic swarm period. We used a fully automated method to measure shear-wave splitting properties. After considering a shear-wave window of 45° and several quality criteria, we determined a complex state of anisotropy, with NE-SW directions of polarization (𝜑) prevailing pre-2020, while a dominant WNW-ESE orientation was observed during the swarm (with secondary NE-SW and N-S trends). The spatial distribution of 𝜑 did not offer any strong correlation with local faults. Additionally, 𝜑 seemed to rotate in 2015 and 2020, with variations of normalized time-delays being present during the crisis. These observations, along with indications regarding fluid diffusion during the swarm, led us to hypothesize that shear-wave splitting in the EGoC is mainly driven by high pressure gradients. A better understanding of pre‑2020 seismicity and more local stations to record future seismicity would be required to further specify the connection between fluid processes and seismic anisotropy in the area.

Техногенная сейсмичность в районе Ленинского каменноугольного месторождения

The paper presents an analysis of seismotectonic conditions in the area of the Leninskoye coal deposit (Kuzbass). The territory of the Leninskiy district is belongs to the coverage zone of the Altai-Sayan regional seismic stations network. The results of research into intensification of seismic activity in the Kuzbass region using the local networks of seismic stations are considered. In the course of seismic observations in the territory of the Kemerovo region four seismically active zones been identified that encircle the largest industrial megacities of Kuzbass and that are responsible for 90% of the earthquake foci. According to the distribution of epicenters of the seismic events, the area of the Leninskoe coal deposit belongs to one of the seismic zones with the most actively developing natural and man-made seismic activity identified within the research. The research indicates that the induced seismic activity in Kuzbass prevails over the natural seismicity.

Lithospheric S Wave Velocity Variations Beneath the Mackenzie Mountains and Northern Canadian Cordillera

AbstractThe Mackenzie Mountains (MMs) in the Yukon and Northwest Territories, Canada, are an enigmatic mountain range. They are currently uplifting (Leonard et al., 2008, https//doi.org/10.1029/2007JB005456), yet are about 700 km from the nearest plate boundary. Their arcuate shape is distinct and extends over 100 km eastward from the general trend of the Northern Canadian Cordillera. To better assess the cause and conditions of the current uplift, we processed ambient seismic noise data from a linear array of broadband seismographs crossing the mountains, along with other regional seismic stations, to estimate Rayleigh wave phase velocities between 6 and 40 s periods. From this, we estimated phase velocity dispersion and performed a tomographic inversion to estimate VS. Tomography reveals a low‐velocity structure that extends upward from the base of the ∼50–66 km thick lithosphere to the upper crust, and we hypothesize that inferred low density and low rigidity associated with the VS anomaly localizes the ongoing uplift and thrust‐dominated seismicity of the MMs. Additionally, we find relatively low crustal velocities that extend to the west of the MMs, suggesting that strain transfer from the Gulf of Alaska plate boundary plays a driving role as the crust translates to the northeast and buckles up against the craton consistent with the orogenic float hypothesis of Mazzotti and Hyndman (2002, https//doi.org/10.1130/0091-7613(2002)030〈0495:YCASTA〉2.0.CO;2). Finally, we observe lithospheric azimuthal anisotropy with an NW‐SE fast direction. This is nearly orthogonal to teleseismic shear wave splitting measurements in the central MMs, and suggests that asthenosphere flow and lithospheric strain are not aligned in this region.

ONOR EARTHQUAKE on August 14, 2016, Mw=5.8 (Sakhalin Island)

On August 14, 2016 at 11h15m UTS there was a strong earthquake with Mw=5.8 in the central part of the Sakhalin Island, which felt in nearby settlements with an intensity of up to Ii=5–6 by the MSK-64 scale. The greatest intensity of shaking was recorded in the village of Onor, closest to the epicenter. Within 2 weeks after the earthquake, more than 130 aftershocks were registered by regional seismic stations. The aftershock zone is extended in the NW-SE direction. Subhorizontal compressional stresses of the NE-SW orientation were realized in the earthquake foci. The type of movement in the source is a reverse-fault with a slight strike-slip component. The fault plane with the south-western dip direction was adopted as an operational. The earthquake source belongs to one of the secondary structures of the Central Sakhalin oblique-reverse fault, which cuts through a section of the Western Sakhalin Mountains in the direction of the western coast. The active block of the fault is the eastern wing, underthrusting under the western one. Based on the results of the macroseismic inspection, theoretical isoseists are calculated and constructed. Such a rare strong earthquake aroused wide interest among specialists and allowed them to test several new methods and technical solutions, as well as obtain new information about the seismicity and tectonics of the Sakhalin region. This article presents a comprehensive overview of seismological information on this earthquake, mainly based on the results of earlier publications.

Results of local seismological monitoring in the Lena delta region

Refinement of the geodynamic situation in the area of the Lena River delta is relevant for understanding local geological processes. Previously, source seismology for this area was provided only by remote regional seismic stations. This paper shows the results of processing data from detailed seismological observations for 2018–2021. The distribution of earthquake hypocenters and their focal mechanisms are presented. The results of processing largely confirm the a priori geological data and do not contradict the results of regional observations. The accumulation of earthquakes in the area of the Kharaulakh Range most likely refers to the Primorsky Fault, which extends along the coast of the Bykovskaya channel. According to geological studies, the Primorsky Fault is a fault, which is confirmed by the focal mechanisms of earthquake sources in this area.

SOURCE PARAMETERS of CRIMEAN-BLACK SEA EARTHQUAKES in 2015

The spectral and dynamic source parameters (М0, r0, , , ησ, , u, Eu and Mw) of 16 Crimean earthquakes with КП=6.5–10.8, restored by amplitude spectra of compression and shear seismic waves recorded by digital regional seismic stations are analyzed. Approximation of the spectra and source parameters calculation is performed in the framework of the Brune dislocation model. The highest values of dynamic parameters (М0, r0, , , ησ, u, EU и Mw) are obtained for the earthquakes on June 13 and August 16 with h=11 km, h=7 km respectively and КП=10.8, which occurred in the Azov-Kuban and Kerch-Anapa areas. The radiation friction r for all earthquakes had a negative value, pointing to a complex slide of the rupture in the source. Within the whole energy range, the average value of the released stress did not exceed Δσ=8∙105 PA (8 bar) and apparent stress ησ &lt;11∙105 PA (11 bar). For most 2015 earthquakes, the average M0 и r0 values were within the confidence intervals of long-term dependencies M0(КП), r0(КП). The values of r0 were evenly distributed concerning the regression r0(КП) and М0 is mostly located below the average according to М0 (КП). The maximum deviations of M0 from the long-term М0(КП) dependence were obtained for the most strong earthquakes on June 13 and August 16 with КП=10.8. These deviations can be associated with participation in average M0 of the "Sevastopol" station data which give low values of М0 and possible errors in determining the focal depths influencing the choice of environment velocity models to calculate М0. For the most strong earthquake of August 16 with Мw=3.8, which occurred in the Kerch-Anapa region, a solution of focal mechanism was obtained. The earthquake occurred under the action of horizontal latitudinal tensile forces. The type of movement in the source is an oblique normal fault. Both nodal planes have near-meridional (STKNP1=167°) and near-diagonal (STKNP2=336°) strike.