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In 2007–2015, Shirshov Institute of Oceanology of the Russian Academy of Sciences (IO RAS) carried out seismological observations in the water area and on the coast of the Baltic Sea using autonomous seismic stations. Here, in the area of the Sambia Peninsula, previously considered aseismic, a strong perceptible earthquake with a magnitude of about M = 4.6 occurred in 2004. The most interesting data were obtained by IO RAS in 2008–2009 from seismological monitoring using autonomous bottom and coastal seismic stations. The data obtained in 2010–2015 turned out to be unsuitable for full-scope processing due to several causes (losses of bottom seismographs, high noise level at coastal stations, etc.). Seismological monitoring in the west of the Kaliningrad region and in the adjoining area of the Baltic Sea detected weak earthquakes with magnitudes ML = 2.5-3 whose sources are confined to the development are of the Kravtsovskoe offshore oil field. Some of these earthquakes have been recorded by the stations of the Norwegian seismic array NORSAR and by the seismic stations of Sweden. The Kravtsovskoe oil field is located on the shelf northwest of the unique natural object, the Curonian Spit. The detected weak earthquakes are likely to be anthropogenic, induced by reservoir pressure disturbances as a result of intensive hydrocarbon production, and are probably precursors of a strong man-made earthquake.

Geophysical Journal International, v. 155, n. 3, p. 981-990, 2003. http://dx.doi.org/10.1111/j.1365-246X.2003.02095.x ; International audience ; Since the decommission of the underground launching control room of the ground-based component of the French nuclear missile system, the whole installation has been turned into a cross-disciplinary underground laboratory. The LSBB is a unique low-noise underground laboratory because of its initial military conception and its location in the regional park of Luberon far from large cities, industry and heavy traffic. The deepest point is 500 m below the surface. At this depth a huge and non-conventional shielded cylindrical capsule is installed with no μ-metal, 1268 m3 in volume, with a residual electromagnetic noise lower than 2 fT Hz−1/2 above 10 Hz. As a result, fluctuations of the Earth's magnetic field under 10 Hz can be recorded at a very low-noise level with a low-Tc SQUID 3-D magnetometer. Taking advantage of the main gallery topology, a broad-band underground seismic array has been deployed since 2001. An analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the Indian earthquake of 2001 January 26 is presented. Evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance (6250 km) is supported by a polarization analysis of seismic and magnetic signals. Spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure.

Geophysical Journal International, v. 155, n. 3, p. 981-990, 2003. http://dx.doi.org/10.1111/j.1365-246X.2003.02095.x ; International audience ; Since the decommission of the underground launching control room of the ground-based component of the French nuclear missile system, the whole installation has been turned into a cross-disciplinary underground laboratory. The LSBB is a unique low-noise underground laboratory because of its initial military conception and its location in the regional park of Luberon far from large cities, industry and heavy traffic. The deepest point is 500 m below the surface. At this depth a huge and non-conventional shielded cylindrical capsule is installed with no μ-metal, 1268 m3 in volume, with a residual electromagnetic noise lower than 2 fT Hz−1/2 above 10 Hz. As a result, fluctuations of the Earth's magnetic field under 10 Hz can be recorded at a very low-noise level with a low-Tc SQUID 3-D magnetometer. Taking advantage of the main gallery topology, a broad-band underground seismic array has been deployed since 2001. An analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the Indian earthquake of 2001 January 26 is presented. Evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance (6250 km) is supported by a polarization analysis of seismic and magnetic signals. Spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure.

Geophysical Journal International, v. 155, n. 3, p. 981-990, 2003. http://dx.doi.org/10.1111/j.1365-246X.2003.02095.x ; International audience ; Since the decommission of the underground launching control room of the ground-based component of the French nuclear missile system, the whole installation has been turned into a cross-disciplinary underground laboratory. The LSBB is a unique low-noise underground laboratory because of its initial military conception and its location in the regional park of Luberon far from large cities, industry and heavy traffic. The deepest point is 500 m below the surface. At this depth a huge and non-conventional shielded cylindrical capsule is installed with no μ-metal, 1268 m3 in volume, with a residual electromagnetic noise lower than 2 fT Hz−1/2 above 10 Hz. As a result, fluctuations of the Earth's magnetic field under 10 Hz can be recorded at a very low-noise level with a low-Tc SQUID 3-D magnetometer. Taking advantage of the main gallery topology, a broad-band underground seismic array has been deployed since 2001. An analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the Indian earthquake of 2001 January 26 is presented. Evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance (6250 km) is supported by a polarization analysis of seismic and magnetic signals. Spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure.

Geophysical Journal International, v. 155, n. 3, p. 981-990, 2003. http://dx.doi.org/10.1111/j.1365-246X.2003.02095.x ; International audience ; Since the decommission of the underground launching control room of the ground-based component of the French nuclear missile system, the whole installation has been turned into a cross-disciplinary underground laboratory. The LSBB is a unique low-noise underground laboratory because of its initial military conception and its location in the regional park of Luberon far from large cities, industry and heavy traffic. The deepest point is 500 m below the surface. At this depth a huge and non-conventional shielded cylindrical capsule is installed with no μ-metal, 1268 m3 in volume, with a residual electromagnetic noise lower than 2 fT Hz−1/2 above 10 Hz. As a result, fluctuations of the Earth's magnetic field under 10 Hz can be recorded at a very low-noise level with a low-Tc SQUID 3-D magnetometer. Taking advantage of the main gallery topology, a broad-band underground seismic array has been deployed since 2001. An analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the Indian earthquake of 2001 January 26 is presented. Evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance (6250 km) is supported by a polarization analysis of seismic and magnetic signals. Spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure.

Geophysical Journal International, v. 155, n. 3, p. 981-990, 2003. http://dx.doi.org/10.1111/j.1365-246X.2003.02095.x ; International audience ; Since the decommission of the underground launching control room of the ground-based component of the French nuclear missile system, the whole installation has been turned into a cross-disciplinary underground laboratory. The LSBB is a unique low-noise underground laboratory because of its initial military conception and its location in the regional park of Luberon far from large cities, industry and heavy traffic. The deepest point is 500 m below the surface. At this depth a huge and non-conventional shielded cylindrical capsule is installed with no μ-metal, 1268 m3 in volume, with a residual electromagnetic noise lower than 2 fT Hz−1/2 above 10 Hz. As a result, fluctuations of the Earth's magnetic field under 10 Hz can be recorded at a very low-noise level with a low-Tc SQUID 3-D magnetometer. Taking advantage of the main gallery topology, a broad-band underground seismic array has been deployed since 2001. An analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the Indian earthquake of 2001 January 26 is presented. Evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance (6250 km) is supported by a polarization analysis of seismic and magnetic signals. Spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure.

Nine earthquakes inside Mesopotamia Plain from 2016 to 2018 were analyzed. Three seismic networks have been relied on to relocate these events and know their responsible fault. These networks are; Mesopotamian Seismological Center, Al-Refaei Seismic Array and Iranian Seismological Center. The results showed that the root mean square (RMS) values for all relocated events ranged between 0.002-0.997. The results of the error ellipse ranged from 0.24 - 4.17 km with longitude and 0.76 - 8.24 km with latitude. The new locations of these events are on or near the Ramadi-Musaiyib Fault. This means that the Ramadi-Musaiyib Fault, which belongs to the Najd fault system, is currently in reactivation.

Tema del mes ; Se presenta una breve reseña de las actividades que la Universidad Nacional Autónoma de México ha realizado durante más de 100 años para el monitoreo del fenómeno sísmico. Tales acciones han estado bajo la responsabilidad de los Institutos de Geofísica e Ingeniería mediante la operación del Servicio Sismológico y la Red Acelerográfica. También se señalan los trabajos de colaboración realizados con el Gobierno Federal para implementar el proyecto denominado la Red Sísmica Mexicana, el cual ha permitido mejorar la cobertura nacional de observación sísmica así como la generación de información pronta y oportuna que incluye en forma inmediata los reportes sísmicos de magnitud y localización epicentral; así como los mapas de intensidad del movimiento tanto a nivel nacional como a nivel local en el valle de México ; In this paper we present those activities that National University Autonomous of Mexico has carried out during more than hundred years of monitoring the seismic phenomena. Such actions have been in charge of the institutes of Geophysics and Engineering Institutes by means of Mexican Seismological Service and the Accelerograph Network. It is also mentioned the joint venture with the Federal Government to implement the project called Mexican Seismic Array which has permitted to improve seismic observation coverage and the generation of appropriate and relevant information as well. Such is the case of the seismic reports that include epicentral location and earthquake magnitude and in the other hand the Shakemaps in the country and particularly in Mexico ́s valley

Tema del mes ; Se presenta una breve reseña de las actividades que la Universidad Nacional Autónoma de México ha realizado durante más de 100 años para el monitoreo del fenómeno sísmico. Tales acciones han estado bajo la responsabilidad de los Institutos de Geofísica e Ingeniería mediante la operación del Servicio Sismológico y la Red Acelerográfica. También se señalan los trabajos de colaboración realizados con el Gobierno Federal para implementar el proyecto denominado la Red Sísmica Mexicana, el cual ha permitido mejorar la cobertura nacional de observación sísmica así como la generación de información pronta y oportuna que incluye en forma inmediata los reportes sísmicos de magnitud y localización epicentral; así como los mapas de intensidad del movimiento tanto a nivel nacional como a nivel local en el valle de México ; In this paper we present those activities that National University Autonomous of Mexico has carried out during more than hundred years of monitoring the seismic phenomena. Such actions have been in charge of the institutes of Geophysics and Engineering Institutes by means of Mexican Seismological Service and the Accelerograph Network. It is also mentioned the joint venture with the Federal Government to implement the project called Mexican Seismic Array which has permitted to improve seismic observation coverage and the generation of appropriate and relevant information as well. Such is the case of the seismic reports that include epicentral location and earthquake magnitude and in the other hand the Shakemaps in the country and particularly in Mexico ́s valley

Hydraulic fracturing at Preston New Road, Lancashire, UK, in August 2019 induced a number of felt earthquakes. The largest event (M 2.9) occurred on August 26th, 2019, approximately 3 days after hydraulic fracturing operations at the site had stopped. Following this, in November 2019, the UK government announced a moratorium on hydraulic fracturing for shale gas in England. Here we provide an analysis of the microseismic observations made during this case of hydraulic fracturing-induced fault activation. More than 55,000 microseismic events were detected during operations using a downhole array, the vast majority measuring less than Mw 0. Event locations revealed the growth of hydraulic fractures and their interaction with several pre-existing structures. The spatiotemporal distribution of events suggests that a hydraulic pathway was created between the injection points and a nearby NW-SE striking fault, on which the largest events occurred. The aftershocks of the ML 2.9 event clearly delineate the rupture plane, with their spatial distribution forming a halo of activity around the mainshock rupture area. Across clusters of events, the magnitude distributions are distinctly bimodal, with a lower Gutenberg-Richter b-value for events above Mw 0, suggesting a break in scaling between events associated with hydraulic fracture propagation, and events associated with activation of the fault. This poses a challenge for mitigation strategies which rely on extrapolating microseismicity observed during injection to forecast future behaviour. The activated fault was well oriented for failure in the regional stress field, significantly more so than the fault activated during previous operations at PNR in 2018. The differing orientations within the stress field likely explain why this PNR-2 fault produced larger events compared to the 2018 sequence, despite receiving a smaller volume of injected fluid. This indicates that fault orientation and in situ stress conditions play a key role in controlling the severity of seismicity induced by hydraulic fracturing.

Abstract. The town of Idrija is located in an area with an increased seismic hazard in W Slovenia and is partly built on alluvial sediments or artificial mining and smelting deposits which can amplify seismic ground motion. There is a need to prepare a comprehensive seismic microzonation in the near future to support seismic hazard and risk assessment. To study the applicability of the microtremor horizontal-to-vertical spectral ratio (HVSR) method for this purpose, 70 free-field microtremor measurements were performed in a town area of 0.8 km2 with 50–200 m spacing between the points. The HVSR analysis has shown that it is possible to derive the sediments' resonance frequency at 48 points. With the remaining one third of the measurements, nearly flat HVSR curves were obtained, indicating a small or negligible impedance contrast with the seismological bedrock. The isofrequency (a range of 2.5–19.5 Hz) and the HVSR peak amplitude (a range of 3–6, with a few larger values) maps were prepared using the natural neighbor interpolation algorithm and compared with the geological map and the map of artificial deposits. Surprisingly no clear correlation was found between the distribution of resonance frequencies or peak amplitudes and the known extent of the supposed soft sediments or deposits. This can be explained by relatively well-compacted and rather stiff deposits and the complex geometry of sedimentary bodies. However, at several individual locations it was possible to correlate the shape and amplitude of the HVSR curve with the known geological structure and prominent site effects were established in different places. In given conditions (very limited free space and a high level of noise) it would be difficult to perform an active seismic refraction or MASW measurements to investigate the S-wave velocity profiles and the thickness of sediments in detail, which would be representative enough for microzonation purposes. The importance of the microtremor method is therefore even greater, because it enables a direct estimation of the resonance frequency without knowing the internal structure and physical properties of the shallow subsurface. The results of this study can be directly used in analyses of the possible occurrence of soil–structure resonance of individual buildings, including important cultural heritage mining and other structures protected by UNESCO. Another application of the derived free-field isofrequency map is to support soil classification according to the recent trends in building codes and to calibrate Vs profiles obtained from the microtremor array or geophysical measurements.