ARCTIC

Magnitude scale inversion for the Ethiopian rift.

The sediment composition of deep-sea cores from the central Arctic Ocean, the Fram Strait, and the Yermak Plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200,000 years. Layers with high amounts of coarse, terrigenous ice-rafted debris (IRD) and often high contents of smectite were deposited during extensive glaciations in northern Eurasia, when ice sheets reached the northern continental margins of the Barents and Kara seas and discharged icebergs into the Arctic Ocean. Intercalated layers with relatively low IRD and smectite contents, but abundant planktic foraminifers in the coarse fraction were deposited during periods of Atlantic Water inflow to the Arctic Ocean and seasonally open waters (leads) in a sea ice cover with only few icebergs in the Arctic Ocean. High IRD contents in the sediments reflect the presence of ice sheets on the Kara and Barents seas shelves and the hinterland during the entire oxygen isotope stage 6 (ca 190-130 ka), in substage 5b (ca 90-80 ka), at the stage boundary 5/4 (around 75 ka), and in late stage 4/early stage 3 (ca 65-50 ka). These results are in excellent correlation with those from recent field work in northern Scandinavia, European Russia, Siberia, and on the shelves. Relatively low amounts of IRD in central Arctic Ocean sediments from the Late Weichselian glacial maximum (ca 24-18 ka) correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time.Oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the Arctic Ocean. The synchroneity of freshwater events and IRD input suggests a common source. Strongest events were associated with deglaciations of the Barents and Kara seas after the ice sheets had blocked the outflow of large rivers for several millennia. The outflow of freshwater from large ice-dammed lakes occurred at ca 130, 80-75, and 52 ka. Freshwater events in the central Arctic Ocean during the last deglaciation (ca 18 ka) were relatively small compared to the previous events. This indicates that during most of the Late Weichselian glacial maximum a river outflow from northern Siberia to the Arctic Ocean was possible.Atlantic Water inflow to the Arctic Ocean and seasonally open waters in the ice (leads) occurred during the interglacials of oxygen isotope stage 1 and substage 5e, during several interstadials (stage 3, substages 5a and 5c), and to a lesser degree within stadials and glacials (stages 2, 4, and 6). With the exception of the interglacials, these periods were times of strong ice growth on the continents as revealed by terrestrial data. The coincidence suggests that open waters in the Arctic Ocean and the Nordic Seas were an important moisture source (in addition to more southerly sources) which fostered the growth of ice sheets on northern Eurasia.

Applying Distributed Acoustic Sensing (DAS) to sense offshore telecom cables offers a unique opportunity to expand permanent seismological networks far offshore with an unprecedented instrumentation density but presents challenges in managing and processing data. This study introduces a workflow for automating earthquake catalog generation by combining DAS arrays with regional on‐land seismic networks. We apply it to the ABYSS offshore permanent observatory in central Chile, which began continuous recording in October 2023 on three 150‐km segments of a regional dark‐fiber telecommunication network. Our workflow includes state‐of‐the‐art components originally developed for conventional seismic sensor data. We first show that PhaseNet, pretrained on conventional seismic stations, can perform automatic phase picking on DAS strain‐rate data converted to velocity. In a second step, we demonstrate that the GaMMA associator, tuned with parameters adapted to our dense data set, can cluster picked arrivals of small and moderate‐sized earthquakes. We then adapt NonLinLoc to compute hypocenter locations using numerous phase picks, combining DAS and onland seismic data for improved accuracy. Finally, we show that reliable local magnitudes can be estimated on DAS recordings using the Richter scale. The earthquake catalog is stored in an SQL database using QuakeML formalism and is accessible via a user‐friendly webpage. By applying the workflow to onshore station recordings, we evaluate the benefits of adding permanent seafloor DAS instrumentation, demonstrating that offshore DAS significantly improves the detection of small‐magnitude earthquakes and reduces the offshore magnitude of completeness to 1.3.

The expedition was organized by the Federal state budgetary institution of science Institute of Oceanology. P. p. Shirshova of the Russian Academy of Sciences for complex Oceanological research in the waters of the Kara sea and the Laptev sea. The works were carried out in accordance with the Permit No. 14-32 / 2 issued by the Ministry of education and science of the Russian Federation on 28 April 2018 to conduct marine scientific research in inland sea waters, in the territorial sea, in the exclusive economic zone and on the continental shelf of the Russian Federation. The expedition was performed under the following programs: “Program of fundamental scientific research of state academies of Sciences for 2013-2020” approved by the decree of the Government of the Russian Federation of 03.12.2012, № 2237- R.; the Plan for marine scientific research in the internal sea waters, in territorial mo-re, in the exclusive economic zone and the continental shelf of the Russian Federation to 2018, approved by the order Ministry of education and science of the Russian Federation No. 1244, paragraph 2, of 21 December, 2017; the consolidated Plan of marine expeditions on research vessels commissioned by THE Fano, approved by the Fano earth hydrosphere Council (Protocol No. 03-00-04/6 of 22.12.2017); State tasks of the participating organizations, including the topics Of the basic research program of the Presidium of the Russian Academy of Sciences 1.3 P, as well as research plans for the projects of the RNF No. 14-50-00095, 16-47-02009. RFBR projects on “Fundamental problems of studying and development of the Russian Arctic: natural and social environment (Arctic)”, RFBR initiative Projects on “ Fundamental problems of studying and development of the Russian Arctic: natural and social environment (Arctic)”.

SeisBlue, a deep-learning-based earthquake monitoring system, is one of the solutions to deal with massive continuous waveform data and create earthquake catalogs. The SeisBlue workflow contains waveform data preprocessing, phase arrival detection by AI modules, phase associator, earthquake locating, earthquake catalog generation, and data visualization. The whole process can be done automatically and efficiently reduces the labor and time costs. In this study, SeisBlue is applied to three different regional seismic networks: the Formosa Array for the observation of magma chamber beneath the Tatun volcanic area, Taiwan (aperture ~80 km with 148 broadband stations and station spacing 5 km), the Chihshang seismic network (CSN) for monitoring micro-seismicity of Chihshang, Taiwan (aperture ~150 km with 14 broadband stations and station spacing 20 km), and the temporary dense nodal array for capturing the aftershock sequence of the 18 th Sep. 2022 Mw6.9 Chihshang earthquake, Taiwan (aperture ~70 km with 46 nodal stations and station spacing 3 km). The 2020 annual SeisBlue catalog of the Formosa Array contains 2,201 earthquakes, as background seismicity, compare to the 1,467 earthquakes listed in the standard catalog of the Central Weather Administration (CWA), Taiwan. The two-month SeisBlue catalog of the 2022 Mw6.9 Chihshang earthquake sequence, September to October, contains 14,276 earthquakes using the CSN dataset; however, the CWA standard catalog only lists 1,247 earthquakes during the same time period. By using waveform data of 18 th Sep. to 25 th Oct. 2022, SeisBlue detects 34,630 and 12,458 earthquakes extracted from the datasets of the dense nodal array and CSN, respectively. SeisBlue can effectively detects both background and aftershock seismicity and extracts small earthquakes via dense arrays.Keywords: AI earthquake monitoring system, deep learning, AI earthquake catalog, SeisBlue, automatic waveform picking

The article is a continuation of the research on creating the most complete and representative earthquake catalogs by combining all available data from regional, national, and international seismological agencies and reducing magnitudes to a uniform scale. The task of identifying and removing duplicates that arise during the merging process is solved using the authors’ modification of the nearest neighbor method. It is evident that the intelligent merging of different earthquake catalogs for the same territory will improve the completeness and representativeness of events in the final integrated catalog. In this article, the earthquake catalog of the western sector of the Arctic zone of the Russian Federation (AZRF) covering the period 1962–2022 was created by merging three regional Russian catalogs and the ISC catalog. The ratio of magnitude types in the catalog for different seismic networks was analyzed, and magnitude estimates were unified based on the obtained ratios. For analyzing seismic activity in the western AZRF, it is recommended to use earthquakes from the period 1998–2020 when the catalog was significantly cleaned from explosions and other events of the “non-earthquake” type.

In July 2013, a sequence of more than 340 earthquakes was induced during the deep geothermal drilling project close to the city of St. Gallen in Switzerland. Induced seismicity represents a disadvantage during sub-surface geoenergy operations, so understanding the underlying triggering mechanisms is crucial for mitigating the seismic hazard.  To this end, we investigate the role of fluids and elastic stress transfer as driving mechanisms of the St. Gallen seismic sequence. Following the underlying idea of the Focal Mechanism Tomography technique, we estimate the excess pore fluid pressure at the hypocenters of earthquakes from the analysis of their focal mechanisms. The uncertainties on the focal mechanism parameters, friction coefficient and rock density are taken into account using a Monte Carlo approach to calculate the effect on the estimated excess pore pressure. The results indicate that, in addition to Coulomb static stress change, high-pressure fluids had a primary role in the earthquake triggering. Unlike what is observed in other geothermal fields, the value of the calculated excess pore fluid pressure is higher than the injection pressure for approximately half of the earthquakes. This can likely be attributed to the accidental release of overpressured gas (gas kick) that occurred during field operations when the seal to a gas reservoir was broken.   This work has been supported by PRIN-2017 MATISSE project (No. 20177EPPN2), funded by Italian Ministry of Education and Research.  

We provide a comprehensive earthquake catalogue for Iran that is suitable for detailed seismological analysis and seismic hazard assessment. Based on the work by (Mousavi-Bafrouei et al. Ann Geophys 57:S0653, 2014) and new sources of data, we extend the uniform Iranian earthquake catalogue to include events from fourth century B.C. to December 31, 2018. Conversion relationships between moment magnitude (Mw) and body wave, surface wave, Nuttli and local magnitudes are presented and used to estimate Mw based on a priority system. The updated earthquake catalogue includes 25,937 earthquakes with Mw between 2.6 and 8.1. Catalogue declustering, using the method of conjugate windows, results in 1772 clusters with 17,123 events with Mw between 2.9 and 8.1. We also evaluate magnitude of completeness and seismicity parameters including the Gutenberg-Richter b-value, mean annual seismic activity rate and maximum expected magnitude in five seismotectonic units. Overall, the Zagros unit has the highest b-value among all units, whereas the Makran unit shows the lowest b-value indicating possibility of the largest range of magnitudes in the region.

Earthquakes cause severe damages to bridge structures, and rocking isolation of piers has become a superior option for the seismic protection of bridges during earthquakes. A seismic isolation method with free rocking mode is proposed for railway bridge piers with medium height. Experimental and numerical analysis are conducted to evaluate the seismic performance of the rocking-isolated bridge pier. Shaking table test is carried out with a scaled model by using three strong input earthquake records. The measured data includes displacement, acceleration and time history response of the pier-top and the bending moment of the pier-bottom. Test results show that the expected uplift and rocking of the isolated pier occur under strong earthquakes and the rocking-isolated pier has self-centering capacity. Slight damage appears at the collision surface between pier and base due to pier uplift, while there is no damage in the pier body. The bending moment of pier-bottom is less affected by the spectrum of input ground motions. The two-spring model is provided to simulate the isolated pier with free rocking mode under earthquakes. A seismic response analysis model for the rocking-ioslated pier is established with the assistance of OpenSees platform. The simulated results agree well with the measured results by shaking table test. Therefore, the seismic isolation method with a self-centering pier is worthy of promotion for railway bridges in high seismic risk regions.

SUMMARY Accurate characterization of the magnitude–frequency distribution of seismicity, and its associated uncertainties, is essential for seismic hazard assessment. This distribution is commonly described by the Gutenberg–Richter (GR) relation, parametrized by the b-value, which has been identified as a potential proxy for investigating many spatiotemporally varying Earth phenomena. Estimating the spatiotemporal variability of b-values often requires windowing, forcing a trade-off between resolution and statistical reliability. New probabilistic methods circumvent this by inferring both the number and locations of change points directly from earthquake catalogues. Nevertheless, accurately determining the b-value remains difficult because the GR relation only holds over a limited range of magnitudes. This research develops a general statistical model to address several methodological challenges in estimating the magnitude–frequency distribution of observed seismicity, including variations in space or time. The approach simultaneously solves for the b-value and magnitude-range limits. This avoids potential bias due to inaccurate manual truncation of earthquake catalogues. The model considers the entire observed catalogue and parametrizes the decay of the distribution at both low and high magnitudes. Consequently, robust uncertainties in estimated b-values reflect uncertainty in the range of magnitudes over which the GR relation is observed to be valid. Importantly, spatiotemporal variations in the parameters that define the magnitude range are considered to be independent from the b-value, as we assume the physical factors that influence the GR relation are independent of the factors that limit the observed earthquake catalogue. We demonstrate this methodology through application to simulated and observed earthquake catalogues. In particular, the value of our approach is highlighted through application to observed records of induced seismicity associated with fluid-injection operations in western Canada. Our results demonstrate accurate b-value estimates and associated uncertainties. Furthermore, the additional parameters that define the magnitude range serve as proxies for other factors including seismic network performance, recording duration, potential geometric limitations on earthquake size and potential injection characteristics (in induced seismicity cases). Our approach also allows for the investigation of how these other factors may vary in space/time. Results from this work contribute to rigorous propagation of accurate b-value estimates, including uncertainties, into subsequent analyses such as seismic hazard models and regulatory protocols that are applied to industrial activity.

Assessing the completeness magnitude Mc of earthquake catalogs is an essential prerequisite for any seismicity analysis. We employ a simple model to com- puteMc inspacebasedontheproximitytoseismicstationsinanetwork.Weshowthata relationship of the form M predd �� ad bc, with d the distance to the kth nearest seismic station, fits the observations well, k depending on the minimum number of stations being required to trigger an event declaration in a catalog. We then propose anewMc mappingapproach,theBayesianmagnitude ofcompleteness (BMC)method, based on a two-step procedure: (1) a spatial resolution optimization to minimize spatial heterogeneities and uncertainties in Mc estimates and (2) a Bayesian approach that merges prior information about Mc based on the proximity to seismic stations with locally observed values weighted by their respective uncertainties. Contrary to the cur- rentMc mappingprocedures,theradiusthatdefineswhichearthquakestoincludeinthe local magnitude distribution is chosen according to an objective criterion, and there are no gaps in the spatial estimation of Mc. The method solely requires the coordinates of seismic stations. Here, we investigate the Taiwan Central Weather Bureau (CWB) seismic network and earthquake catalog over the period 1994-2010.

Online material : Earthquake catalog; coordinates of source zones; list of events in each zone; frequency magnitude distribution plots. Identification and characterization of seismic sources are essential input for seismic hazard analysis. A complete and consistent catalog of earthquakes in a region can offer good data for studying the distribution of earthquakes with respect to space, time, and magnitude. Earthquakes are known to have occurred in the region of the Indian subcontinent from historic times. Most of the activities, including many great earthquakes, have occurred in the northern subcontinent and in the Andaman and Nicobar regions. In the southern peninsula, damaging earthquakes have occurred, but their frequency was less and magnitudes were lower than the plate boundary earthquakes. The tectonic framework of the Indian subcontinent—an area of about 3.2 million square kilometers—is complex and varied spatially. This necessitates identifying different regions of similar seismicity. In this study we attempt to identify and characterize regional seismic source zones based on a homogeneous catalog of earthquakes in and around India from 250 BC until 2010. We identified different regional seismic source zones and created separate catalogs for each respective zone. Most earthquake catalogs do not report earthquake magnitudes consistently over time, which may hinder defining seismicity patterns or assessing seismic hazards. The magnitude scales used for earthquake catalogs in India are not homogeneous. Compiling a complete catalog of earthquakes with uniform magnitudes is essential for defining seismicity patterns and assessing seismic hazards for a region (Chen and Tsai 2008). Hence the original magnitudes of earthquakes have to be converted to a common and reliable magnitude scale using appropriate magnitude correlations. In the raw catalog, many events can be dependent events that occurred in association with a mainshock in a cluster. These aftershocks and foreshocks have to be removed from the catalog using …

The detection level of a seismic network is a measure of its effective ability to record small earthquakes in a given area. It can vary in both space and time and depends on several factors such as meteorological conditions, anthropic noise, local soil conditions—all factors that affect the seismic noise level—as well as the quality and operating condition of the instruments. The ability to estimate the level of detection is of tremendous importance both in the design of a new network and in determining whether a given network can recognize seismicity consistently or needs to be improved in some of its parts. In this article, we determine the detection level of the Cuban seismic network using the empirically estimated seismic noise spectral level at each station site and some theoretical relationships to predict the signal amplitude of a seismic event at individual stations. The minimum local detectable magnitude thus depends on some network parameters such as the signal-to-noise ratio and the number of stations used in the calculation. We also demonstrate the effectiveness of our predictions by comparing the estimated detection level with those empirically determined from one year of data (i.e., the year 2020) of the Cuban seismic catalog. Our analysis shows, on the one hand, in which areas the current Cuban network should be improved, also depending on the regional pattern of faults, and, on the other hand, indicates the magnitude threshold that can be assumed homogeneously for the catalog of Cuban earthquakes in 2020. Because the adopted method can use current measurements of the seismic noise level (e.g., daily), the proposed analysis can also be configured for continuous monitoring of network state quality.

SUMMARY The northern Chile Triple Junction (CTJ) is characterized by the ongoing subduction of the Nazca plate beneath the South American plate. The geological structures within the subduction zone undergo complex changes, resulting in significant tectonic activities and intense seismicity along the western margin of South America. Based on the Gravity Recovery and Climate Experiment (GRACE) data and earthquake catalogues, this study selects the northern CTJ area (25° S–40° S, 75° W–65° W) as the research object, adopts the mathematical methods of independent component analysis (ICA) and principal component analysis (PCA) to separate the earthquake-related signals within the GRACE data, and fits the changes of seismic b-values through the frequency–magnitude relationship. The characteristics of gravity changes before and after seismic events, the seismic activity parameter b-values, and the relationship between the gravity signals and b-values are discussed. The results show that mathematical methods can effectively extract seismic-related gravity components from the GRACE data. ICA, compared to PCA, provides better results in capturing the temporal variations associated with b-value time-series, which exhibit good consistency in long-term trend changes. The average change of b-values in the study area is 0.66 ± 0.003, fluctuating over time. Generally, prior to larger seismic events, b-values tend to decrease. Along the western margin of South America, b-values are low; this aligns with the active tectonic activities between subducting plates. Additionally, a certain correlation between b-values and gravity changes is observed, but due to the influence of tectonic activities, the correspondence between b-values and gravity anomalies may not be consistent across different areas. The b-value is highly consistent with the strain rate model. Low b-values correspond to high strain rates along the western edge of South America, which is in line with the tectonic characteristics of frequent seismic activity in this area. A gradual concentration of gravity anomalies before major earthquakes is observed, accompanied by the gradual accumulation of smaller seismic events. Meanwhile, several months before the two major earthquakes, the spatial distribution of gravity appears to be similar to the coseismic signals, but the nature of its generation remains to be explored. These methods and results not only add to the applications of GRACE in seismic studies but also raise questions for further exploration.

Over the past two decades, there have been several initiatives to create volunteer‐based seismic networks. The Personal Seismic Network, proposed around 1990, used a short‐period seismograph to record earthquake waveforms using existing phone lines (Cranswick and Banfill, 1990; Cranswick et al. , 1993). NetQuakes (Luetgert et al. , 2010) deploys triaxial Micro‐Electromechanical Systems (MEMS) sensors in private homes, businesses, and public buildings where there is an Internet connection. Other seismic networks using a dense array of low‐cost MEMS sensors are the Community Seismic Network (Clayton et al. , 2012; Kohler et al. , 2013) and the Home Seismometer Network (Horiuchi et al. , 2009). One main advantage of combining low‐cost MEMS sensors and existing Internet connection in public and private buildings over the traditional networks is the reduction in installation and maintenance costs (Koide et al. , 2006). In doing so, it is possible to create a dense seismic network for a fraction of the cost of traditional seismic networks (D’Alessandro and D’Anna, 2013; D’Alessandro, 2014; D’Alessandro et al. , 2014). A rapidly deployable and highly mobile seismic network can collect enormous volumes of data at high spatial density during an aftershock sequence following major earthquakes (Naito et al. , 2013). Although the low‐cost seismic networks described above were primarily designed to detect and characterize earthquakes, the networks have also been used for other purposes such as to monitor building health in Kohler et al. (2013). These types of low‐cost networks may also have other potential applications such as detecting landslides (Azzam et al. , 2011) and locating explosions (Taylor et al. , 2011). The Quake‐Catcher Network (QCN) is another variant of a cyber‐social seismic network, which has been operating since 2008. Cochran, Lawrence, Christensen, and Chung (2009) and Cochran, Lawrence, Christensen, and Jakka (2009) describe the implementation that uses a client software phase‐picking …