Local Seismic Stations Research Articles

Seismic evidence for break-off of the Molucca Sea slab

The Molucca Sea region is an active arc-arc collision zone whose structure and mantle dynamics are essential for reconstructing the tectonic evolution of Southeast Asia. The key to understanding the tectonic processes of the region is to clarify the morphology of the subducted slabs. However, geometric details of the subducted Molucca Sea slab and other slab segments under this region remain controversial due to the lack of high-resolution mantle tomography. In this study, we jointly invert a large number of local and teleseismic travel-time data recorded at 99 local seismic stations to determine a high-resolution model of P-wave mantle tomography beneath the Molucca Sea region. Our tomography reveals two aseismic slab segments in the deep upper mantle and the mantle transition zone, which may reflect the earlier subducted Molucca Sea slab. The total length of the Molucca Sea slab is estimated to be ∼1800 to 1900 km, being ∼300 km longer than previous estimates.

The 4 January 2020 offshore Pearl River Estuary earthquake sequence in South China: Implications for seismic potential of the NW-striking local faults

The complexity of intraplate earthquakes and their challenge to current earthquake models persist as an important scientific and social problem, both about their causes and the resulting hazards. The Guangdong-Hong Kong-Macao Greater Bay area (GHMGB) is located in the coastal seismic zone of South China. Due to the huge residential population and important economic status, seismic hazard in the GHMGB often causes widespread concern. In this work, waveform data of the 2020 Pearl River Estuary (PRE) earthquake (ML3.5) and its aftershocks are carefully analyzed using about 6-month data recorded at 124 local seismic stations. A total of 8 aftershocks are identified.We determine the hypocentral parameters of the PRE mainshock and its aftershocks, as well as their focal mechanisms.Our results show that the 2020 PRE earthquake sequence is distributed in a NW-SE direction with a lateral extent of about 3.5 km, which is consistent with the location of the NW-striking Qi'Ao-Guishan fault. The 2020 PRE earthquake and its aftershocks exhibit similar focal mechanisms. According to the stereographic projection results of the P and T axes, the orientation of the principal compressive stress is oblique to the NW-striking Qi'Ao-Guishan fault, hence these earthquakes are mainly characterized by left-lateral strike-slip faulting. In combination with many previous geological and geophysical results, we suggest that the NW-striking faults could have similar seismogenic importance as the NE-striking faults in the GHMGB and even the whole coast of the northern South China Sea, especially at the intersection of the NW- and NE-trending faults.

Onset of a submarine eruption east of Mayotte, Comoros archipelago: the first ten months seismicity of the seismo-volcanic sequence (2018–2019)

From 10 May 2018 to 1 November 2022 (time of writing), an unprecedented seismic activity is observed east of Mayotte Island (France), related to the largest submarine eruption ever recorded with offshore geophysical studies. Using signals from regional and local seismic stations, we build a comprehensive catalog of the local seismicity for the first ten months of the sequence. This catalog includes a total of 2874 events of magnitude (Mlv) ranging from 2.4 to 6.0, with 77% of them relocated using a double difference location procedure. The hypocentral locations over this period are highly dependent on the small seismic network available. Therefore we compare the locations of later events using a similar network and those estimated from a local ocean bottom seismometer (OBS) network installed since March 2019. Based on the time space evolution and characteristics of the seismicity, five distinct phases can be identified, corresponding to the successive activation of two deep seismic swarms, related to the lithospheric-scale magma ascent up to the seafloor, along with progressive deepening of the seismicity interpreted as decompression of a 40 km deep reservoir.

Seismic Observation and Location of a Meteor Burst From a Dense Station Deployment in Southern Spain

AbstractA meteor event on 11 December 2016 in southern Spain was accompanied by an audible boom and felt vibrations. Acousto‐seismic coupling of the near‐field pressure wave has been recorded by an unusually large number of 44 local seismic stations. Considering the ERA5 atmospheric temperature and wind speed model, we can attribute the seismic detections to a point source at 38 km height, coincident with the most luminous fragmentation event recorded by meteor cameras. We show and analyze waveforms, spectrograms and signal polarization along a dense, temporary broadband transect in the area. Seismic records show important differences between them, like large variability in polarization, amplitudes and frequency content, emphasizing the role of local effects. The duration and complexity of waveforms can be attributed to path and site effects, including multipathing through small‐scale atmospheric heterogeneity and scattering of the incoming acoustic wavefield at local topography.

Nucleation Process of the 2017 Nuugaatsiaq, Greenland Landslide

Seismic precursors prior to the failure of rocks are essential for probing the nucleation process and mitigating hazards. However, such precursory events before large landslides are rarely reported possibly due to the lack of near-source observations. The 2017 Nuugaatsiaq, Greenland landslide that was preceded by an abundance of small earthquakes and captured by a local seismic station is a notable exception and offers us a valuable opportunity to investigate how a large landslide initiated. Prior work suggests that accelerated creeping plays an important role during the landslide nucleation process. However, by analyzing the temporal evolution of the waveform similarities, waveform amplitudes, and inter-event times of the seismic precursors, we find that the Nuugaatsiaq landslide was very likely triggered by a series of accelerated and migratory small earthquakes approaching the nucleation area of the upcoming landslide, thus providing important insights into the failure initiation of massive landslides.

Crustal focal mechanisms in the NW sierras de cordoba, and connections with mio-pliocene basement thrusting of the easternmost Sierras Pampeanas, south-Central Andes

The seismicity studied in this paper is located along the back arc region, between 30°35′ and 31°52’ S latitude, in the morphostructural unit known as Eastern Sierras Pampeanas. Seventeen crustal earthquakes could be identified and located, between June 2004 and March 2018, using seismic data recorded by the broadband seismological network of National Institute for Seismic Prevention (INPRES), combined with free seismic data from the Incorporated Research Institutions for Seismology (IRIS). Focal mechanisms were calculated from localized seismicity using the P-wave first motions and interpreted as a strain style on the western portion of Sierras de Córdoba. Overall, the seismicity in this region during the study period was constrained to the upper ∼25 km of the crust and is mostly concentrated along minor structures and not along the major range-bounding faults. Although there is evidence of quaternary activity along the larger structures, the relationship between these displacements and modern deformations is not well developed due to the lack of local seismic stations in the area and the long recurrence interval between earthquakes of significant magnitudes. However, very recent morphometric studies in the Sierras Pampeanas have analyzed the main topography controls and suggested relatively higher uplift rates in the central sectors of the Sierra de Pocho, and a balance between tectonic uplift and erosion rates. Nevertheless, three seismic events showed greater depths around 36 km according to previously proposed geological and geophysical models of crustal thickness and mohorovicic depth. Although focal mechanism solutions show varied results, distributed throughout all the region, it is possible to determine an inverse deformation with an oblique component assigned to regional faults and an area where a normal deformation with an oblique component predominates, near to the Ojo de Agua Lineament. Accordingly with seismological observations, we proposed a model in which the seismogenic structures seem to have detached from deep horizontal intra-crustal interfaces that affects the faults and brittle structures, which document that the Eastern Sierras Pampeanas are actively deforming in response to compression from the convergent margin.

Nucleation mechanism of the 2021 Mw 7.4 Maduo earthquake, NE Tibetan Plateau: Insights from seismic tomography and numerical modeling

The 2021 Mw 7.4 Maduo earthquake ruptured the Jiangcuo fault, a secondary fault within the Bayan Har block, NE Tibetan Plateau, which attests that large earthquakes can occur on faults with very low slip rates. In this study, we use data from local seismic stations to explore the 3D velocity structure beneath the source region of the Maduo earthquake. Our results indicate that there is a distinct low-velocity anomaly in the mid-lower crust, and the thickness of this low-velocity zone decreases sharply to the east. The Maduo earthquake occurred in the transition zone between the high- and low-velocity regions. Based on our local velocity model and our knowledge of the regional crustal structures, we constructed numerical models to investigate the stress and strain energy distributions in our study area. As indicated by the stress concentration, strain energy accumulation, and low strain rate in the shallow upper crust around the source region, we conclude that the seismic velocity heterogeneity and the weak ductile mid-lower crust provide a unique tectonic environment that facilitated the nucleation of the Maduo earthquake. This study helps to understand the mechanisms of the Maduo earthquake, and more importantly reconciles the seeming contradiction between large earthquakes and low slip and strain rates.

Moment tensor catalogue of earthquakes in West Bohemia from 2008 to 2018

Abstract. We present a unique catalogue of full moment tensors (MTs) of earthquakes with ML between 0.5 and 4.4 that occurred in West Bohemia, Czech Republic, in the period from 2008 to 2018 (Vavryčuk et al., 2022a, b). The MTs were calculated from vertical components of P-wave amplitudes. The MT inversion was based on principal component analysis applied to optimally filtered velocity records of local seismic stations deployed in the West Bohemia area. The minimum number of inverted stations is 15, and the rms between theoretical and observed amplitudes is lower than 0.5. The catalogue is exceptional in several aspects: (1) it represents an extraordinary, extensive dataset of more than 5100 MTs; (2) it covers a long period of seismicity in the studied area, during which several prominent earthquake swarms took place; (3) the locations and retrieved MTs of earthquakes are of a high accuracy. Additionally, we provide three-component records at the West Bohemia (WEBNET) seismic stations, the velocity model in the region, and the technical specification of the stations. The dataset is ideal for being utilized by a large community of researchers for various seismological purposes, e.g. for studies of (1) the migration of foci and the spatiotemporal evolution of seismicity, (2) redistribution of stress during periods of intense seismicity, (3) the interaction of faults, (4) the Coulomb stress along the faults and local stress anomalies connected to fault irregularities, (5) diffusivity of fluids along the activated faults, or (6) the time-dependent seismic risk due to the migration of seismicity in the region. In addition, the dataset is optimum for developing and testing new inversions for MTs and for tectonic stress. Since most of the earthquakes are non-shear, the dataset can contribute to studies of non-double-couple components of MTs and their relation to shear–tensile fracturing and/or seismic anisotropy in the focal zone.

Focal Mechanisms of West Bohemia, Central Europe, Earthquakes—End of May 2014: Evidence of Volume Changes

Abstract West Bohemia is a region with a lot of mineral springs and gas outflows, which seems to be related to the remains of Quaternary volcanism in Central Europe. Earthquake swarms in shallow depths (less than 15 km) are very frequent there. We focused on the strongest earthquake over the past 30 yr (31 May, 2014 Mw∼3.8) and on two smaller ones (Mw∼2.9 and 2.5) from the same day. Seismograms from local and regional seismic stations were used to calculate the full and deviatoric moment tensors using low-frequency full-waveform inversion. The studied events have similar source mechanisms. The aforementioned earthquake sequence was selected to observe the isotropic part (negative value = implosion) of full moment tensors. It could relate to the motion and phase transition of fluids, especially water, and CO2. The main goal of this study is to contribute to clarification of the nature of earthquake swarms in the western edge of the Bohemian Massif. Negative value of the isotropic part of full moment tensor could be related to the closing of cracks and fissures during a rupture process.

Use of Local Seismic Network in Analysis of Volcano-Tectonic (VT) Events Preceding the 2017 Agung Volcano Eruption (Bali, Indonesia)

This study provides an attempt to analyze the pre-eruptive seismicity events for volcano eruption forecasting. After more than 50 years of slumber, Agung volcano on Bali Island erupted explosively, starting on November 21, 2017. The eruption was preceded by almost 2 months of significant increase of recorded seismicity, herein defined as “seismic crisis.” Our study provides the first analysis of VT events using data from eight local seismic stations deployed by the Center for Volcanology and Geological Hazard Mitigation of Indonesia (CVGHM) to monitor the Agung Volcano activity. In total, 2,726 Volcano-Tectonic (VT) events, with 13,023 P waves and 11,823 S wave phases, were successfully identified between October 18 and November 30, 2017. We increased the accuracy of the hypocenter locations of these VT events using a double-difference (DD) relative relocation and a new velocity model appropriate to the subsurface geological conditions of Agung volcano. We found two types of seismicity during the recording period that represent the VT events relating to fracture network reactivation due to stress changes (during the seismic crisis) and magma intrusion (after the seismic crisis). The characteristics of each event type are discussed in terms of Vp/Vs values, phase delay times, seismic cluster shapes, and waveform similarity. We interpret that the upward migrating magma reached a barrier (probably a stiff layer) which prohibited further ascent. Consequently, magma pressurized the zone above the magma chamber and beneath the barrier, reactivated the fracture zone between Agung and Batur volcanoes, and caused the seismic crisis since September 2017. In early November 2017, the barrier was finally intruded, and magma and seismicity propagated toward the Agung summit. This reconstruction provides a better depth constraint as to the previous conceptual models and explains the long delay (∼10 weeks) between the onset of the seismic crisis and the eruption. The distinction between the fracture reactivation and magma intrusion VT events observed in this study is significant for eruption forecasting and understanding the subsurface structure of the magmatic system. Based on the results obtained in this study, we emphasize the importance of prompt analysis (location and basic seismic characteristics) of the seismic crisis preceding the Agung eruption.

Local earthquake tomography of the source region of the 2018 Lombok earthquake sequence, Indonesia

SUMMARY We develop and present a 3-D seismic velocity model of the source region of the 2018 Lombok, Indonesia earthquakes by using local earthquake tomography. The data consist of 28 728 P- and 20 713 S-wave arrival times from 3259 events which were recorded by 20 local seismic stations. The results show that most of the significant earthquakes occur to the edge of high-velocity regions. We interpret these to represent coherent blocks of the Flores Oceanic Crust underthrusting Lombok. At depths shallower than the nucleation area of the largest earthquake, many triggered aftershocks are located within a low-velocity, high-Vp/Vs region which is probably a highly fractured fault zone with a large amount of fluid. This fault zone is parallel to the dip of the Flores Back Arc Thrust and probably ruptured during this earthquake sequence. A prominent low-velocity, high-Vp/Vs region is colocated with the northwest and southern flank of the Rinjani volcanic complex. This large aseismic region is probably related to a wide area of the crust containing fluids due to ongoing magma intrusion beneath the volcano. To the east of Rinjani Volcano a cooled intrusive complex was imaged. It is characterized by high-velocity and low-Vp/Vs, supported by the presence of a high Bouguer anomaly. We confirm the existence of the Sumbawa Strait Strike-Slip Fault and find it is characterized by an elongated low-velocity, high-Vp/Vs zone.

Preliminary Report on the 18 May 2020 Ms 5.0 Qiaojia Earthquake, Yunnan, China

AbstractThe 18 May 2020 Ms 5.0 Qiaojia earthquake occurred in Qiaojia County, Yunnan Province, ∼25 km away from the 3 August 2014 Ms 6.5 Ludian earthquake. This earthquake was well recorded by dense local seismic stations of the Qiaojia array constructed near the Xiaojiang fault zone. The focal mechanism of the mainshock exhibited strike-slip motion with a centroid depth of 8 km. We determined the seismogenic fault of the Qiaojia earthquake using aftershock relocation with local dense seismic arrays. The mainshock is located on a previously unmapped fault. Aftershocks clearly delineated east–west rupture plane, which was not revealed by the regional seismic network due to relatively sparse stations. The length and width of the aftershock zone are ∼5 km and 3 km, respectively. The focal mechanisms of 70 aftershocks with magnitudes ML≥1.0 showed similar focal mechanism with the mainshock. The stress field inverted from focal mechanisms of the aftershocks is consistent with the tectonic stress field. The coseismic and postseismic static coulomb stress changes show that the Ludian earthquake has a negative impact on the Qiaojia earthquake with a value of −0.01 MPa, implying that the Qiaojia earthquake was unlikely statically triggered by the Ludian earthquake. The Qiaojia earthquake sequence was characterized by low b-value and low-decay rate in the aftershock area, indicating high-seismic risk in this region. The dense seismic observation allows us to study the moderate earthquake in detail and provides us with valuable information of near-fault seismicity to analyze earthquake hazard and the potential of large earthquakes in the future.

EAST EUROPEAN PLATFORM. RUSSIAN PART

It is reported that 22 stationary seismic stations, 2 arrays and 7 local seismic stations, located in the area of Novovoronezh and Kursk nuclear stations, monitor seismicity of the Russian territory of the East European platform (EEP). A new station Belogornoe with high registration class has been opened, which also belongs to the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty (IMS CTBTO). The results of the microseismic noise study at the Pulkovo network stations and assessment of maximum distance of earthquake registration in the Voronezh crystalline massif are presented. In 2014, relatively strong earthquakes with М3.0 were not recorded on the Russian territory of the EEP. Weaker natural seismicity with M≤2 was recorded in Karelia and the border areas with Finland, near Kandalaksha Bay, near the Khibiny Massif on the Kola Peninsula and on the territory of the Voronezh Crystalline Massif. Observations of local networks near nuclear stations are aimed at updating the information on seismicity previously considered as an aseismic territory of the EEP. Man-made events were recorded in permanent quarries, the most powerful of them (M=3.1–3.3) were produced in the quarries on the territory of the Kursk magnetic anomaly.

The Electrochemical Seismometer Based on Fine-Tune Sensing Electrodes for Undersea Exploration

This paper developed micro-electro-mechanical system (MEMS) based electrochemical seismometers featured with new structures of sensing electrodes for undersea exploration. In comparison to previously reported counterparts, the proposed sensing electrodes were featured with 1) simplification of the fabrication processes and 2) convenient control of the tiny space between anodes and cathodes by the adoption of insulating annuluses and make an increase in the sensitivities (e.g. 5200 V/(m/s) @1Hz). Based on forced-balanced feedback systems, the broadband seismometers were developed with the final bandwidth of 0.0083Hz-20Hz and achieves the sensitivity of 2000V/(m/s) with the noise level of 1.26(nm/s)/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> @1Hz (-178dB). Under the detection of a nature earthquake, the cross-correlation coefficients between the proposed seismometers and a local seismic station reach 0.95. As a proof-of-concept demonstration, the seismometers developed in this study were tested in a sea-trial, and shown to function well on a sea bed (e.g. 1000 m in depth) with cross-correlation coefficients between two devices quantified as 0.94.

Analysis of Seismic Methods Used for Subsea Hydrocarbon Exploration

Subsea hydrocarbon exploration comprises detection and estimation of shape, depth, volume and other physical properties of hydrocarbon fields within the Earth’s subsurface layers. Marine seismic survey is a process that generally includes sending seismic waves into seabed and recording the intensity and travel time of reflected seismic waves to determine the subsurface features of the Earth. Different methods, equipment and techniques are used to conduct a survey, from sea surface seismic arrays to seabed local seismic station networks. In this paper different widely used seismic methods are presented, together with their advantages and drawbacks. Furthermore, new methods that are being developed and tested for future approach to more advanced and efficient seismic exploration are presented.

Sharp Lateral Moho Variations Across the SE Tibetan Margin and Their Implications for Plateau Growth

AbstractThe tectonic uplift of the Tibetan Plateau is a focus in the geosciences. Middle‐lower crustal flow is a popular model to interpret the geodynamic mechanism on the margin of the Tibetan Plateau. The model predicts different surface and Moho topographies across the plateau boundary due to the different strengths of the surrounding blocks, that is, sharp boundaries on the eastern plateau boundary and gentle variations in the southeastern plateau boundary. Here, we employ receiver function and common conversion point stacking analysis with the seismic waveforms recorded by the dense ChinArray and other local seismic stations to accurately define the Moho topography in southeastern (SE) Tibet. We find that the Moho under the Tibetan Plateau is much deeper than that under the surrounding Yangtze Craton and Indochina block; abrupt Moho changes are found across the southeastern plateau margin, similar to that under the eastern plateau margin. We interpret these sharp Moho variations across the plateau margin to have developed when the Tibetan Plateau was extruded southeastward in the late Miocene. Subsequent gravity collapse resulted in crustal extension and gentle topographic variation, while the sharp Moho slope was preserved.

Evolving infrasound detections from Bogoslof volcano, Alaska: insights from atmospheric propagation modeling

Bogoslof volcano, a back-arc volcano in Alaska’s Aleutian arc, began an eruptive sequence in mid-December 2016 that ended in late August 2017, with 70 individual eruptive episodes. Because there were no local seismic or infrasound stations on the island, the Alaska Volcano Observatory (AVO) relied on distant geophysical networks and remote sensing techniques to assess activity during the eruption. AVO maintains six infrasound arrays to monitor activity along the Aleutian arc: Adak, the Island of Four Mountains, Okmok, Akutan, Sand Point, and Dillingham. Eruption detection at infrasound arrays is subject to local as well as mesoscale meteorological conditions that vary greatly over both short and long timescales. Infrasound detections from the array nearest to Bogoslof (Okmok), with a latency of about 3 min, played a crucial role in monitoring activity during the eruption. Despite the relative proximity of the Okmok array to Bogoslof (60 km), infrasound detections were not uniformly observed with only about two-thirds of the events successfully detected. The farthest array at Dillingham (816 km) detected approximately half of the explosive events, with all other arrays detecting less than half of the events. We compare observations with infrasound propagation model predictions, using both normal mode and parabolic equation forward models, to interpret the variation in detections of the 70 explosive events across the AVO infrasound network. The forward models utilize the newly created, publicly available AVO-G2S atmospheric reconstruction using numerical weather predictions data for the lower atmosphere, coupled with upper atmosphere empirical models of wind speeds and temperature. We find that long-range detections (> 100 km) of Bogoslof events are largely aligned with seasonal variability in favorable propagation conditions, while regional detections (< 100 km) are less consistent with propagation modeling. Understanding the output of numerical models in comparison to past observations will facilitate their use in future operational settings for AVO and other observatories.

High Bulk and Shear Attenuation Due to Partial Melt in the Tonga‐Lau Back‐arc Mantle

AbstractSeismic attenuation measures energy loss during seismic wave propagation and quantifies the relaxation of rocks' elastic moduli. Abundant seismic studies have observed shear attenuation, but few have quantified bulk attenuation (bulk modulus relaxation), and these studies controversially locate finite bulk attenuation in different parts of the Earth, from the asthenosphere to the inner core. Here we present conclusive evidence localizing bulk attenuation to a specific region of the uppermost mantle. By analyzing amplitude spectral decay of P and S waves from Tonga earthquakes recorded at local seismic stations, we observe unusually low QP/QS ratios (&lt;1.5) in the Tonga‐Lau mantle wedge. All seismic raypaths with significant path‐average bulk attenuation (Qκ−1 &gt; 0.01 or Qκ &lt; 100) are confined to the region immediately beneath the Lau back‐arc spreading centers west of the Tonga Arc. Tomography results show that the highest bulk attenuation (Qκ−1 = 0.037 ± 0.008 or Qκ = 27.0 ± 0.2) is about 75% of the in situ shear attenuation. The observed high bulk attenuation anomalies coincide with an inferred zone of partial melting, suggesting that the causative mechanism involves either infinitesimal movement of melt through pores or changes in melt fraction in response to seismic waves.

Moho determination from GOCE gradiometry data over Ethiopia

The gravity field and steady-state ocean circulation explorer (GOCE) satellite mission has a good global coverage of data except across the Polar Regions. Here, the goal is to take the advantage of such a coverage over Ethiopia and use the 2nd order radial derivative of the Earth's gravitational potential for determining a Moho model for this territory. In order to compute Moho depth, we used the Vening Meinesz-Moritz (VMM) theory of isostasy and the GOCE 2nd order radial derivatives are inverted using an integral equation in combination with effects of topographic/bathymetric, sediment and consolidated crystalline masses and considering density contrast model derived from CRUST1.0. The GOCE derived Moho depth over Ethiopia varies from 24.9 to 44.8 km. More specifically, the Moho depth ranges outside of the rift valley from 33.9 to 44.4 km and from 25.5 to 44.8 km across the western and eastern plateaus of Ethiopia respectively. In addition, inside the main Ethiopian rift system the Moho depth varies from 24.9 to 41.5 km where the minimum occur in the Afar region. We compare our Moho model with that of CRUST1.0, Meier 05, M13_Eurasia, GEMMA models and 82 local seismic stations over Ethiopia. The result showed, respectively, standard deviations of 5.3, 4.9, 8.1, 5.0 and 4.0 km with respect to these Moho models. Our Moho model is closer to the local seismic stations than other models.

АРКТИЧЕСКИЙ БАССЕЙН

The review of the Arctic basin seismicity for 2013 is presented. It is based mainly on the data from the sta-tions of world network, located outside the basin. The data from a single local seismic station was used. It was "Franz Josef Land" station with two sets of seismic sensors, ZF1 and ZF2. The station is a part the Ar-khangelsk network, operating in the region since September 2011. There were 38 earthquakes with mb=3.0–4.6 in the Arctic basin in total. A map of their epicenters is provided. 28 of them are connected with the seismically active zone, which extends through the deep-water part of the Arctic basin to the shelf of the Laptev Sea. For two earthquakes, the parameters of focal mechanisms are given according to the GCMT da-ta. The magnitude frequency distribution for 2013 is compared with the distributions for 1990-2012. The level of seismic energy released in 2013 is 1.3 times lower than in 2012 and 1.6 times higher than its average one for 23 previous years. The distribution of earthquakes in the Arctic region in 2013 is presented.