Seismic Stations Research Articles

Comparisons and characteristics of site amplifications using noise and earthquake data: Examples from the Malta Seismic Network

In the past decade, numerous studies on the amplification effects due to the local geology have been conducted in the Maltese islands (Central Mediterranean). Due to the lack of permanent seismic stations on geological areas of concern, ambient noise techniques were utilised. The areas of interest are characterised by clay, that can reach a thickness of 75 m, buried beneath limestone which introduces a velocity inversion in the stratigraphy. With the expansion of the Malta Seismic Network (MSN) to three stations in such zones, the possibility of confirming and further investigating the results using empirical data arises. Here we present results, using 3 years of data including time domain and frequency-domain analysis in terms of Standard Spectral Ratio (SSR) and earthquake H/V. In particular, we note that the amplifications obtained using the SSR technique are significantly higher than those obtained using both noise and earthquake H/V techniques. Additional peaks below 1 Hz of significant amplitude are also obtained on the SSR curves. By separating the earthquake data set on the basis of distance from the islands, we show that this amplification is source-dependent, and that the high amplification values originate from larger, more distant earthquakes in the Hellenic arc.

New Insights on the Seismic Activity of Ostuni (Apulia Region, Southern Italy) Offshore

On 23 March 2018, an event of magnitude ML 3.9 occurred about 10 km from the town of Ostuni, in the Adriatic offshore. It was the most energetic earthquake in South–Central Apulia ever recorded instrumentally. On 13 February 2019, in the same area, a second ML 3.3 event was recorded. The analysis of the 2018 event shows that the ambiguity of the solution of the fault plane reported by INGV (Istituto Nazionale di Geofisica e Vulcanologia) on the Italian National Earthquake Centre website can be solved considering existing seismic profiles, exploration well logs and the Quaternary activity of faults in the epicentral area. A seismogenic source was identified in the rupture of a small portion of a 40 km length structure with strike NW-SE, dipping at a high angle toward the south. In this work, we have relocated the recent earthquakes by using the seismic stations managed by the University of Bari (UniBa), one of which is quite close to the event’s epicenter (about 20 km), together with data coming from the RSN (Rete Sismica Nazionale). Furthermore, we have determined the focal mechanism of some events, with implications on stress field of the area. Our results show right-lateral transtensional kinematics of the seismogenic faults along approximately E-W striking planes, with a tension, T, with a trend of about 60° (NE-SW direction) and a plunge of 20°. Finally, we have tried to correlate the location of the four best constrained earthquakes with their seismogenic structures.

Tracking Multiyear Sea‐Ice Variation in the Arctic Ocean Over Decades With Microseism

AbstractWe construct a linear model of microseism power as a function of sea‐ice concentration and ocean‐wave activity with a seismic station located on northern Ellesmere Island. The influence of wind‐ice‐ocean interactions on microseism has been taken into account. We find the increase in microseism power over the last 32 years reflects the long‐term loss of sea ice and increasing ocean‐wave activity in the Arctic Ocean likely associated with climate change. We further assess model performance to determine a representative region over which sea‐ice concentration and ocean‐wave activity most directly influence the microseism power. The seismological methods developed here suggest that there is the potential to augment or refine observations of sea‐ice conditions obtained from satellites and from in‐situ observations. Seismological methods may thus help determine properties such as sea‐ice thickness, which are less amenable to conventional observations, under a changing climate, particularly in remote areas like the High Arctic.

Microseism Amplitude and Wave Power in the Mediterranean Sea (1996–2023)

AbstractIn this work, we integrate seismic data recorded by nine coastal Mediterranean seismic stations and wave hindcast data for 1 January 1996 through 15 October 2023. We examine the relationships between the ocean wave‐generated microseism signal (the most continuous and ubiquitous seismic signal on Earth) in terms of temporally varying spectral content, root mean square amplitude, and microseism power spectral density, with the main features of principal ocean wave attributes, specifically significant wave heights, wave period and wave power. To explore relationships between microseism and sea state, we performed a correlation analysis between seismic root square mean amplitude and significant wave height time series for the entire Mediterranean Sea for 1996–2023, including retrieving long‐term trends for microseism energy and independently estimated wave power and calculating the Spearman correlation coefficient between the two trend time series. Despite the small number of stations available the analysis allows for a useful exploratory study on the microseism and its relationship with Mediterranean Sea state and wave power spanning 27 years. Given the recent increase in the number of regional seismic stations, the growth of data sharing, and the intensification of global warming and climate extreme events, the results and methods explored here can be further implemented and developed in coming years for coastal monitoring purposes in complement with other data sources.

Dynamically triggered seismicity in Japan following the 2024 Mw7.5 Noto earthquake

Abstract On January 1st, 2024, a moment magnitude (M w ) 7.5 earthquake occurred on an active reverse fault in the northern part of Noto Peninsula, being one of the largest intraplate events recorded in Japan. In previous studies, the dynamic triggering of seismicity in Japan following some large remote earthquakes has been well documented, such as in the case of the 2011 M w 9.0 Tohoku–Oki earthquake, the 2016 M w 7.1 Kumamoto earthquake, and other large teleseismic events. In this study, we investigate the remote triggering of microearthquakes by the 2024 Noto earthquake and their characteristics. We analyze waveform data recorded at high-sensitivity seismic stations in Japan, before and after the occurrence of the Noto mainshock. Local earthquakes are detected on high-pass filtered three-component seismograms. Low-pass filtered waveforms are used for visualizing the mainshock surface waves and estimating dynamic stresses. Our results show a relatively widespread activation of small earthquakes—none of them listed in the Japan Meteorological Agency (JMA) earthquake catalog—that were triggered by the passage of the mainshock surface waves in many regions of Japan. These include Hokkaido and Tohoku in northeastern Japan, Kanto in central Japan, and Kyushu in southern Japan. The triggering is mostly observed in volcanic regions, supporting the hypothesis that such places are relatively easy to be activated dynamically, likely due to the excitation of fluids by the passage of mainshock surface waves. The calculated dynamic stress changes estimated from peak ground velocities, which triggered the earthquakes after the Noto mainshock, are in the range 12.8–102.6 kPa. We also report potential, less well-constrained dynamic triggering by the Mw 5.3 Noto foreshock, which occurred ~ 4 min before the mainshock, at levels of stress about 100 times smaller. The analysis of a longer-term (1 month) seismicity pattern, based on the JMA catalog, revealed a statistically significant increase of seismicity in the remote Akita–Yakeyama (Tohoku region) volcanic area, following the Noto earthquake. Graphical Abstract

Обнаружение сейсмических событий на основе искусственной нейронной сети SeisDetNet. Часть 1. Архитектура нейронной сети

An artificial neural network, SeisDetNet, has been developed for distinguishing seismic events from seismic noise based on waveform records. The international STEAD database, which contains minute-long records of local earthquakes and seismic noise, was used as the data source for training, validation, and testing. Specifically, we selected waveforms from 27 seismic stations located in Kyrgyzstan and surrounding areas from the KRNET, KNET, KZ, G, and TJ networks, present in the STEAD database. The model architecture is a combination of a convolutional network, designed to extract key features for class separation, and a fully connected network for the task of classifying the input record as either a seismic event or seismic noise. Evaluating the model on the test set showed good results, with the following binary classification metrics: accuracy of 0.983, precision of 0.989, recall of 0.982, and F1-score of 0.985.

A New Catalogue and Insights into the 2022 Adriatic Offshore Seismic Sequence Using a Machine Learning-Based Procedure.

This paper presents a new catalogue of the 2022/2023 Adriatic Offshore Seismic Sequence obtained by machine learning-based processing. The procedure performs the automatic picking and association of phases starting from the analysis of the continuous waveforms recorded by 40 seismic stations of the Italian National Seismic Network and 5 stations of the SISMIKO emergency group network. The earthquakes were detected over a 3-month period, between 1 November 2022 and 31 January 2023. This new catalogue consists of 2780 earthquakes with a magnitude equal to or greater than ML 0.4, providing more information about lower-magnitude earthquakes in particular. The results make available, on the one hand, new insights into the offshore sequence, which can contribute to confirming the attribution of the earthquakes to the Adriatic Fault System, and in particular, the mainshocks to the Cornelia fault thrust, as also hypothesised by other works in the literature. Moreover, the work provides a further contribution in showing the great potential of using machine learning-based procedures to build catalogues with a greater degree of completeness, even in very particular cases such as the one represented by the Adriatic offshore sequence, for which the minimum distance from the epicentres is high and the azimuth coverage limited.

New local magnitude scales for Egypt

AbstractLocal magnitude (ML) scales have been developed for Egypt based on 14,453 normalized Wood–Anderson amplitudes from 1670 earthquakes. These events were recorded by at least four seismic stations, with hypocentral depths of less than 40 km and earthquake magnitudes ranging from 0.1 to 6.5 ML. The dataset was processed using recordings from the two horizontal components. Egypt was divided into four sub-tectonic regions: South Egypt, North Egypt, the Red Sea, and the Mediterranean Sea. The decay of amplitudes with distance was examined across the entire dataset, providing attenuation characteristics segmented into three sections, with transition distances at 90 km and 175 km. Within each sub-tectonic region, the coefficients of the distance correction term (− log A0) and the station correction term (S) were determined using a trilinear geometrical scattering model and singular value decomposition, respectively. The newly derived relationship for Egypt has resulted in unbiased ML magnitude estimates over a substantial distance range (10–1000 km), thus ensuring consistent magnitude estimates from the ENSN network.

The Seismic Station and Site Amplification Service: Continuously Updated Information on Italian Seismic Stations

Abstract We present STATION (Seismic sTATion and sIte amplificatiON—see Data and Resources), the prototype of an innovative service aimed at providing updated information on specific seismological characteristics of more than 2500 Italian and European seismic stations, belonging to both permanent and temporary networks. The stations are characterized by exploiting recordings from about 120,000 earthquakes that have occurred in Italy and neighboring regions in the period from 2005 to 2024. This extensive database includes local magnitude residuals, horizontal-to-vertical spectral ratios (HVSRs), and mean noise spectra, enabling detailed site-specific seismic assessments as well as supporting postevent analyses. Not only is STATION equipped with a user-friendly web interface, but its seismological products can also be accessed directly through specific station queries (see Data and Resources), enabling quick retrieval of scientific results (e.g., HVSR) and associated metadata, which in turn increases the efficiency of the service itself and its interoperability with other web services. The STATION database is designed to be continually updated and expanded as new data become available from the scientific community (e.g., from the installation of new seismic stations and the recording of new earthquakes). Possible future developments and improvements to the service may include the dynamic updating of the database; the introduction of directional HVSRs and summary maps showing the amplification distribution; the dissemination of individual HVSR curves and spectra for specific requests; the calculation and dissemination of probabilistic distributions of noise power spectral densities; the integration of additional parameters describing site amplification effects; its potential extension to other European and possibly non-European regions.

SEISMICITY of KYRGYZSTAN and UZBEKISTAN in 2020

The system of seismic observations оn the territory of Kyrgyzstan and Uzbekistan in 2020 re mained unchanged: the seismic network of Kyrgyzstan included 26 seismic stations; in Uzbekistan the data from 41 seismic stations were used. Compared to last year, seismic activity in the region has increased: the number of strong earthquakes has increased, most of them occurred in the border areas of China and Tajikistan. The consol idated catalog for 2020 included 261 events with KR≥8.6. The strongest event was the earthquake with KR=14.5, occurred in China on January 19 at 13h27m. On January 17, it was preceded by two foreshocks with energy classes KR=12.9 and KR=10.8. The main shock was accompanied by many aftershocks, the strongest of which had the energy class KR=12.5. On the territory of Kyrgyzstan directly, two rather strong events took place in the border area with China: on February 15 with KR=12.0 and on May 6 with KR=12.5. On the territory of Uzbekistan, three strong earthquakes were registered: on March 26 with KR=11.8, on November 6 with KR=12.4 and on December 26 with KR=11.9.

Seismic Background Noise Level and Station Detectability in the Flores Sea

The Flores back-arc thrust fissure is a significant contributor to earthquake events in the Flores Sea region, as evidenced by seismic investigations. As part of the endeavor to mitigate earthquake risk, seismic data investigations are necessary due to the high potential for earthquakes in the Flores Sea. Background noise in earthquakes is the term used to describe the micro vibrations that are perpetually produced as a result of natural phenomena, such as ocean waves, wind, or human activities. It is crucial to investigate this cacophony in seismology in order to distinguish the primary earthquake signal. Its spectrum analysis can assist in the identification of land changes and the prediction of tectonic activity. This analysis was conducted by employing the Incorporated Research Institutions for Seismology (IRIS) client function as a fetch data tool and the Modular Utility for Statistical Knowledge Gathering Data browser as a data quality monitoring system to verify the health and reliability of seismic data. The three station sites closest to the Flores Sea are the focus of this research data examination. The study's findings indicate that the recorded data at the station is still dominated by cultural noise, as evidenced by the analysis of the probability density function, power spectral density, and noise spectrograms. Additionally, each station exhibits activity with degrees of probability noise that are both high and variable. These results highlight the need for advanced techniques to filter cultural noise and improve the accuracy of seismic signal interpretation in this region. This analysis contributes to understanding tectonic activity in the Flores Sea and underscores the importance of continuous monitoring for earthquake preparedness and risk reduction.

SEISMICITY of AZERBAIJAN and ADJACENT TERRITORIES in 2020

In 2020, the network of seismic stations in Azerbaijan continued to operate without changes and consisted of 35 digital stations. Recordings from three Georgian and two Turkish stations were also used in the processing. To estimate the magnitude of earthquakes, the local magnitude ML Аzr was determined. The total num ber of earthquakes recorded by the network of stations in Azerbaijan was 6619, however, the catalog of earthquakes in Azerbaijan and adjacent territories, published in the appendix to this article, provides the parameters of only 207 earthquakes with a magnitude of ML Аzr3.0. The seismic energy released in the territory of “Azerbaijan” in 2020 (E=2.41013 J) increased by an order of magnitude compared to (E=3.311012 J in 2019, with a slight decrease in the number of earthquakes (N=6619 compared from N=6880 in 2019). The most significant earth quakes directly on the territory of the republic in 2020 were the earthquakes on October 25 with ML Аzr=3.4 and November 4 with ML Аzr=4.2, which were felt with an intensity of 4 points in the nearest settlements.

Database of seismological observations in the Severomuysky region of the Baikal rift during the operation of the local network of stations

The Severomuysky region should be considered as one of the key areas of the northeastern flank of the Baikal rift zone. The most important infrastructure facilities of the Baikal-Amur Mainline, in particular the Severomuysky tunnel, require an objective assessment of the seismic hazard of this territory. The work on converting a unique set of seismological data obtained during the period of operation of the analog local network of seismic stations (1978-1993) into digital format was carried out at the BB GS RAS in order to ensure the safety of all primary seismological observation materials and comprehensive analysis. This information was presented in printed form only. A database has been developed. It provides a relational approach to storing and managing large volumes of data. The database contains complete information on 15,832 earthquakes with KP=4–13 (station information, catalogues, bulletins, etc.). A client application has been created for convenient work with the database. The article illustrates examples of working with a database when solving typical seismological problems. It is obvious that extensive seismological information presented in digital form is of great importance for assessment of seismic hazard of the study under region.

SEISMICITY of the KOPETDAG REGION in 2020

Seismic monitoring of the Kopetdag region in 2020 was carried out by a network of 34 seismic stations of the Institute of Seismology and Atmospheric Physics of the Academy of Sciences of Turkmenistan. 219 earthquakes with energy class KR≥8.6 were included in published catalog, of which 16 events were tangible, including one outside the Kopetdag region. For 37 earthquakes, focal mechanisms were determined. Three largest seismic events in the region with KR=13, occurred on September 6, September 26 and November 25 in the Elbur and Turkmen-Khorasan regions, in the zone of the Elbur-Kopet Dag seismic lineament of northeastern strike, represented a single seismotectonic process development with the movement of epicenters to the northeast, along the specified seismic lineament. The focal mechanisms of all three events are left-lateral strike-slip faults with northeast-oriented nodal planes. Another earthquake with KR=13 was registered on January 2, 2020 outside the region, 213 km southwest of Serhetabad (Turkmenistan), where it was felt with an intensity I=2 by MSK-64 scale. The maximum perceptibility on the territory of Turkmenistan were earthquakes on September 26 and November 25 with KR=13, which manifested themselves in the nearest settlements with an intensity of I=4. In general, in the Kopetdag region in 2020, the total number of representative earthquakes with KR≥8.6 (N=219), seismic activity (A10=0.041) and released seismic energy E=6.7⸳1013 J) increased compared to the parameters of the previous year, approaching long-term average values.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2020

On the Russian territory of the East European Platform, seismic observations were carried out by 47 stationary seismic stations. In 2020, 36 seismic events of tectonic and technogenic-tectonic nature were registered. As before, weak natural and man-made seismicity was recorded on the territory of the Voronezh crystalline massif and the Baltic Shield: in Karelia, border areas with Finland, near the Kandalaksha Bay, within the Khibiny, Kovdor massifs and in the Vite-Guba area of Imandra lake on the Kola Peninsula. A feature of seismicity in 2020 is the occurrence of earthquakes in the paleorift structures of the northeast of the East European Platform: in the Kirov Kazhim and Central Russian aulacogens. The total volume of seismic energy released in 2020 is Е=7.16·109 J, which is 2 times lower than in 2019, but 2 times more than the energy released in 2018.

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.

SEISMICITY of YAKUTIA in 2020

Based on the materials obtained from 20 stationary digital seismic stations of the Yakutia Branch of Geophysical Survey of the Russian Academy of Sciences, the results of seismic monitoring of the territory of the Republic of Sakha (Yakutia) are presented. A total of 360 earthquakes with energy class KR≥7.2 and magnitude M≥1.8 were registered. In 2019 their number was 380. Epicenters of ground shocks traced the large seismic belts (Baikal-Stanovoy and Arctic-Asian) crossing the study area. Significant seismic activity was established in the area of the Chersky Ridge, where repeated ground shocks were noted, confined to the epicentral fields of already known strong earthquakes in the territory of Yakutia. Also, in the Laptev Sea, in the north-east of the region, the maximum number of events in 2020 was determined. A map of epicenters was plotted for the entire territory of the Republic and the seismotectonic situation in 12 seismically active areas was analyzed. In general, the level of seismic energy decreased compared to the previous year.

SEISMICITY of the AMUR and PRIMORYE, SAKHALIN and the KURIL-OKHOTSK REGION in 2020

A review of the Amur and Primorye, Sakhalin, and the Kuril-Okhotsk region seismicity for 2020 is presented on the basis of data from the regional network of stationary seismic stations of the Sakhalin branch of the Geophysical Survey RAS with the involvement of data from adjacent seismological Russian and foreign agencies. Parameters of 2038 seismic events have been determined. Focal mechanisms were calculated for 43 earthquakes, 65 earthquakes have shown a macroseismic effect. A map of the epicenters is presented, the dis tribution of the number N of crustal and deep-focus earthquakes by a magnitude, a total seismic energy E for seismically active areas of three regions are given, in comparison with the average parameters previous years. The significant seismic events are described. The seismicity of the Priamurye and Primorye, Sakhalin, and the Kuril Okhotsk region in 2020 can be characterized as a moderate one within the background level.

SEISMICITY of THE NORTH-EAST of RUSSIA in 2020

The results of seismic monitoring of the Magadan region, Chukotka Autonomous Area and the shelf of adjacent seas (Okhotsk, Chukchi, Bering and East Siberian seas) are considered. There were 12 working seismic stations in the region. The catalog of the Russian North-East earthquakes for 2020 includes information about 327 earthquakes, 114 of them are out of the region and 213 with energy classes KR=6.2–12.2 are within the region borders. As usual, most of 213 regional earthquakes (80 %) are localized in the Kolyma area. The total seismic energy released within the region’s borders was equal ΣЕ=3.4481012 J. The classification of Russian North-East earthquakes was performed using energy classes KР of T.G. Rautian’s scale. The energy representa tiveness map of earthquakes with Кmin=6–10 was built. The Magadan network of stations records without omis sions the earthquakes with Kmin=7 in Magadan oblast, with Kmin=8 in Okhotsk sea, Kmin=10 in the Chukchi. The strongest earthquake of 2020 with KR=12.2 (mb=4.3, Ms=3.7) occurred on November 1, 11h44m in the Bering Sea. Epicenters of Magadan region earthquakes were plotted on the tectonic zoning scheme. Most earthquakes are confined to the largest deep faults in the northwestern and sublatitudinal directions. All hypocenters are located within the earth's crust. In 2020, the seismicity level of the North-East of Russia according to the “SOUS09” scale was assessed as "background average" for the observation period from 1968 to 2020. Spatially, all Russian North-East earthquakes are traditionally con centrated in large seismogenic belts: Chersky, North-Okhotsk and Trans-Beringian.

SEISMICITY of NORTHERN EURASIA in 2020

In 2020, monitoring of seismicity in Northern Eurasia, consisting of 16 regions of Russia and neighboring countries, was carried out by networks of seismic stations in Russia, Azerbaijan, Armenia, Belarus, Kazakhstan, Kyrgyzstan, Moldova, Tajikistan, Turkmenistan, Uzbekistan and Ukraine. In total, the networks included 675 digital, two analogue stations and eight seismic groups. Based on regional catalogs, a consolidated catalog of earthquakes in Northern Eurasia, containing 28,348 tectonic earthquakes, was created. About 21 thousand of them are located in the earth’s crust (h<70 km), more than 7 thousand are at intermediate depths (h=70–300 km), and only 90 are at depths greater than 300 km. In most regions, the seismic process occurred in the background. The total seismic energy released in the specified territory in 2020 (Ean=3.42∙1016 J) was lower than the average annual level for the previous period 2006–2019 (Ean=4.83∙1016 J), but significantly exceeded the energy for 2019 (Ean=0.62∙1016 J).