Seismoactive Regions Research Articles

Geoelectrical structure and monitoring in fault zones of Uimon depression in Gorny Altai region using electromagnetic methods

In this paper we present the results of our studies of sections of the Uimon basin in Gorny Altai (Russia) using a complex of electrical prospecting methods. The areas of Baratal Formation at the surface have been investigated. This areas explored in order to understand the stages of formation of the depression. In addition, the possibilities of the electrotomography method for regular observations in seismoactive regions are shown. Comparison of the amplitudes of the resistivity variations based on repeated ERT measurements in different zones of the Terekta fault indicates the activity of its eastern part, which is expressed in significant resistivity variations exceeding 100%. At the same time, the variations in the northwestern part of the fault, reaching 15% on average, are many times smaller.

Assessment and recognition of pre- and co-seismic electromagnetic signatures from magnetotelluric data: a case study from Koyna–Warna seismoactive region, India

Continuously monitored magnetotelluric (MT) time series data were used to identify the short-term earthquake co-seismic and pre-seismic electromagnetic phenomenon. The co-seismic behavior of the MT time series data recorded at 15 Hz sampling frequency is analyzed for the earthquake that occurred on November 24, 2007, of Mw = 4.6. The wavelet analysis of the MT time series data shows significant enhancement at 3–6 Hz frequency band in the scalogram during the earthquake in comparison with pre- and post-time. The significant enhancement in the scalogram is related to the onset of the main shock of the earthquake. In this paper, we have also shown the precursory signatures of several earthquake magnitudes (Mw) ranging from 3.9 to 4.9 and the focal depth extending from 5 to 10 km mainly dominated by normal and strike-slip faulting. The spectral polarization ratio technique was implemented on these events to identify the precursory signatures. A few days before the earthquake, a significant anomaly was identified for most of the earthquakes using this technique. This prominent anomaly is correlated with Dst index, which provides information about the ionosphere and magnetosphere responses in the presence of the solar wind and interplanetary magnetic field. We inferred the unusual behavior prior to the earthquake is related to the precursory signature, but not related to the solar-terrestrial effect. The complex tectonic settings in the study region suggest that both electrokinetic and seismic dynamo mechanisms are the probable mechanisms playing an important role in generation of co- and pre-seismic electromagnetic signals.

Statistical Analysis of Precision Water Level Data from Observations in a Seismoactive Region: Case Study of the YuZ-5 Well, Kamchatka

A new method is presented for statistical analysis of long-term time series of water level observations aimed at distinguishing short-term disturbances; observation data from the YuZ-5 well, located in the Petropavlovsk Geodynamic Test Area, eastern Kamchatka, are considered. These data (from July 27, 2012, to February 1, 2018) are remarkable for their degree of detail: the sampling rate of the water level and atmospheric pressure measurements was 5 min and the sensitivity (accuracy) was ±0.1 cm for water level recording and ±0.1 hPa for atmospheric pressure. Also, five strong earthquakes with Mw = 6.5–8.3 occurred at epicentral distances of de = 80–700 km during the observation period. A thorough analysis of the hydrodynamic regime of the observation well over a long period and the high quality of observation data, together with the data on strong seismic events, allow us to consider the possibility of using formalized statistical methods of water level data processing for diagnostics of anomalous conditions. As a result of factor and cluster analysis applied to the sequence of multidimensional vectors of the statistical properties of water level time series in successive one-day-long time windows, after adaptive compensation for atmospheric pressure, four different statistically significant states of time series, replacing each other in time, are distinguished. Geophysical interpretation of the anomalous conditions of the water level time series (with a probability of 0.013) is carried out in comparison to strong earthquakes, technical conditions of observations, and seasonal features of the hydrodynamic regime in the observation well. It is shown that this method of water level data processing can detect short-term anomalies in the hydrogeodynamic regime of a well, significantly supplementing traditional processing of water level data aimed mostly at finding low-frequency trends in water level changes. This method can be applied in geophysical monitoring and prediction of earthquakes from online processing of water level data in wells.

Single Layer Recurrent Neural Network for detection of local swarm-like earthquakes—the application

SUMMARYWe present results of applying a local event detector based on artificial neural networks (ANNs) to two seismically active regions. The concept of ANNs enables us to recognize earthquake-like signals in seismograms because well-trained neural networks are characterized by the ability to generalize to unseen examples. This means that once the ANN is trained, in our case by few tens to hundreds of examples of local event seismograms, the algorithm can then recognize similar features in unknown records. The detailed description of the single-station detection, design and training of the ANN has been described in our previous paper. Here we show the practical application of our ANN to the same seismoactive region we used for its training, West Bohemia/Vogtland (border area Czechia-Saxony, local seismic network WEBNET), and to different seismogenic area, Reykjanes Peninsula (South-West Iceland, local seismic network REYKJANET). The training process requires carefully prepared data set which is preferably achieved by manual processing. Such data were available for the West Bohemia/Vogtland earthquake-swarm region, so we used them to train the ANN and test its performance. Due to the absence of completely manually processed activity for the Reykjanes Peninsula, we use the trained ANN for swarm-like activity in such a different tectonic setting. The application of a coincidence of the single-station detections helps to reduce significantly the number of undetected events as well as the number of false alarms. Setting up the minimum number of stations which are required to confirm an event detection enables us to choose the balance between minimum magnitude threshold and a number of false alarms. The ANN detection results for the Reykjanes Peninsula are compared to manual readings on the stations of the REYKJANET network, manual processing from Icelandic regional network SIL (the SIL catalogues by the Icelandic Meteorological Office) and two tested automatic location algorithms. The neural network shows persuasively better detection results in terms of completeness than the SIL catalogues and automatic location algorithms. Subsequently, we show that our ANN is capable of detecting events from various focal zones in West Bohemia/Vogtland although mainly the focal zone of Nový Kostel was used for training. The performance of our detector is comparable to an expert manual processing and we can state that no important event is missed this way even in case of complicated multiple events during the earthquake swarms.

Variations of seismic activity caused by the Chandler Wobble

The problem of the correlation of the global dynamic phenomenon “Chandler wobble” with the local dynamics in different parts of the Earth’s crust and lithosphere is wide of the solution. In this study, an attempt was made to approach the solution by analyzing the temporal variations of local seismic activity in the restricted geospace volumes (GSV) within the uniform seismoactive regions. The driver of Chandler wobble is the deep mantle – the most hard and most massive Earth’s layer, whose large inertia tensor value is able to keep up Chandler’s specific rotation of the Earth for a long time. We use the geocentric coordinate system where daily rotation is absent. In this system Chandler wobble is very slow rotation of the Earth around the current equatorial axis (the pole of which is denoted as EP14). Probably, this slow rotation can influence on the seismic events in the GSV. This influence is proposed to determine by the some statistical parameter EP14gsv that indicates the most typical position EP14 on equator when the most part of the earthquakes have occurred in the given GSV. For some geospace volumes the distribution indicates certain longitudes, where the number of seismic events is maximal or minimal.

Displays of clouds anomalies on the sattelite images before strong earthquakes

Studying of clouds anomalies on the satellite images of seismoactive regions before strong earthquakes which have occurred accordingly on November, 9th, 2002, on April, 6th, 2009 and on October, 18th, 2011 in areas of the cities Anapa (Russia), Aqviilla (Italy) and Van (Turkey) is executed.

Evaluation of the deformation parameters of the northern part of Egypt using Global Navigation Satellite System (GNSS)

The northern part of Egypt is a rapidly growing development accompanied by the increased levels of standard living particularly in its urban areas. From tectonic and seismic point of views, the northern part of Egypt is one of the interested regions. It shows an active geologic structure attributed to the tectonic movements of the African and Eurasian plates from one side and the Arabian plate from the other side. From historical point of view and recent instrumental records, the northern part of Egypt is one of the seismo-active regions in Egypt. The investigations of the seismic events and their interpretations had led to evaluate the seismic hazard for disaster mitigation, for the safety of the densely populated regions and the vital projects. In addition to the monitoring of the seismic events, the most powerful technique of Global Navigation Satellite System (GNSS) will be used in determining crustal deformation where a geodetic network covers the northern part of Egypt. Joining the GPS Permanent stations of the northern part of Egypt with the Southern part of Europe will give a clear picture about the recent crustal deformation and the African plate velocity. The results from the data sets are compared and combined in order to determine the main characteristics of the deformation and hazard estimation for specified regions. Final compiled output from the seismological and geodetic analysis will throw lights upon the geodynamical regime of these seismo-active regions. This work will throw lights upon the geodynamical regime and to delineate the crustal stress and strain fields in the study region. This also enables to evaluate the active tectonics and surface deformation with their directions from repeated geodetic observations. The results show that the area under study suffers from continuous seismic activity related to the crustal movements taken place along trends of major faults

Pre-seismic variations of atmospheric radon activity as a possible reason for abnormal atmospheric effects

Possible atmospheric effects associated with pre-seismic variations of atmospheric radon concentration occasionally observed prior to earthquake occurrence are subjected to theoretical study in order to assess their potential effectiveness. Altitude distribution of atmospheric conductivity is examined as a function of radon and aerosol concentrations. Horizontal components of atmospheric electric fields and currents, which can arise near a boundary of seismo-active region, are estimated. We speculated that changes in radon-induced air ionization can have an impact on fair-weather spectra of ULF electric pulsations. Particular emphasis has been placed on hypothesis for correlation between variations of pre-seismic radon activity and upward thermal radiation measured by satellite over the high seismicity regions. This hypothesis is based on assumption that the radon-induced ionization of atmospheric surface layer can trigger water vapor condensation which in turn results in release of the vaporization heat. Our analysis has shown that the upward thermal flux has to be many orders of magnitude lower than that predicted on the basis of this hypothesis.

Seismic hazard assessment for oil-and-gas-bearing shelf zones: A case study of the North Caspian region

Seismic hazard assessment is done for oil field areas in the North Caspian region by a method earlier successfully applied to other areas. The method involves general seismic zoning data, available regional databases on recurrence of seismic shaking, known models of ground motion attenuation in seismoactive regions, and data on geological and geophysical surveys in the studied area. The assigned level of seismic hazard of the region is refined using probabilistic analysis; additionally, disaggregation is made and accelerograms are synthesized (the latter are necessary for seismic microzoning of particular sites using the numerical nonlinear analysis of ground seismic response). The amplitude and spectral characteristics of ground motions are obtained which are necessary for seismic resistance design and construction of petroleum industry objects.

Seismoactive morphostrctures of the east of Eurasia

The comparison of materials of morphostructural and paleoseismogeological investigations for the East of Eurasia was made. As a result the series of previously unknown seismoactive morphostructures, morphostructural zones and regions were discovered. These data testify to the more high level of seismic danger in this region than it was considered earlier. Therefore, compiling new maps of seismic zoning on the morphostructural-and-paleoseismogeological base as well as actions for people and economy protection from possible strong earthquakes are the most actual now.

Six-degree-of-freedom near-source seismic motions II: examples of real seismogram analysis and S-wave velocity retrieval

Near-source records obtained by the mechanical seismic sensor Rotaphone are presented. The Rotaphone can measure six components of seismic movements, three translational and three rotational. The apparent S-wave phase velocity is determined and the possibility to obtain the wavepath S-wave velocity directly under the receiver is discussed. Rotation-to-translation ratios (RTRs) characterize the strength of rotations compared to translations. The Rotaphone records of local microearthquakes were obtained in various European seismoactive regions over the last few years. Three case studies, analyzed in detail, include various geological structures and seismograms recorded at various epicentral distances from 0.7 to 14.9 km. Also, the source depth varies from 4.8 to 10.4 km. The first case is an event from the West Bohemia intraplate seismic swarm region. The seismogram was recorded only 0.7 km from the epicenter. This case shows the complexity of rotation-to-translational relations near the epicenter. The second case is from the Corinthian Gulf active-rift region. The study confirms the expectation of the theory concerning rotations connected with the direct S wave; however, difficulties follow from a very complex 3D geological structure in the vicinity of the station, complicated by a distinctive topography with steep slopes of the hills. The third example is from South Iceland, near the active Katla volcano. The data in this case satisfy the rotation-to-translation relations very well, which is probably caused by the relatively simple geological setting and appropriate source-to-receiver configuration. The RTRs are computed for all three cases, and their frequency dependence is discussed.

5 years of measurement of electromagnetic emission in West Bohemian seismoactive region

In the previous work we discovered a possible correlation between seismic activity in West Bohemia (Czech Rep.) and electro-magnetic emission (hereafter EME) during earthquake swarm in 2008 year (frequency range of observation: 0.2 – 10 Hz). Since then the EME observation has been continuing for 5 years. We present new results of EME observation during two consecutive swarms (in years 2011 and 2013) – we have to conclude, that the statistical correlation observed during 2008 year swarm was observed only partly and weakly for 2011 year swarm and it was not confirmed for the 2013 year swarm. We are not able to explain observed fact (due to heuristic and statistical character of original hypotheses), it can be an accidental correlation (in 2008 year), but the effect could also vanish for weaker swarms (i.e. for 2011 year and especially for 2013 year), or it could be an effect of different medium property round the hypocenters (the seismic activity migrates to the north with time). ARTICLE INFO Article history: Received 10 September 2013 Accepted 14 February 2014 Available online 3 March 2014

Multiparameter monitoring of electromagnetic earthquake precursors in the frequency range 0.1 Hz-1 MHz

An approach to monitoring of electromagnetic earthquake precursors including variations of the apparent resistivity, electrotelluric fields, electromagnetic emission, and ionospheric disturbances perspective for short-term and mid-term earthquake prediction is considered. Parameters of hardware-software systems for audio- and radiomagnetotelluric soundings used in the monitoring of these precursors in a wide range of frequencies from 0.1 Hz to 1 MHz are described. The technique for the stress-strain sensitive area selection for the creation of monitoring networks based on the analysis of geological and geophysical characteristics of seismo active regions, study of geoelectric structures of preselected sites, and monitoring test sessions with the assessment of the response on tidal media deformations is presented. Recommendations on the recording technique of earthquake electromagnetic precursors are provided.

The seismic moment tensor of earthquakes in the Pribaikalye Region based on surface waves

The most complete characterization of the stress– strain state of the lithosphere in seismoactive regions based on seismological data can be obtained by calcu� lation of seismic moment tensors (SMT) and their fur� ther analysis. In the Pribaikalye Region, the percent� age of experimentally determined SMT, which is an important characteristic of a source, is generally small, about 1% (CMT catalog, NEIC, USGS [1–4]), because the routine estimation of focal mechanisms for most earthquakes is regularly implemented based on the polarities of first arrivals of body waves,

Regularities in the manifestation of earthquake precursors in the ionosphere and near-surface atmospheric electric fields in Kamchatka

The data of hourly measurements of ionospheric parameters in Petropavlovsk-Kamchatsk are analyzed for the period 1998–2002. In the vertical component of near-surface atmospheric quasistatic electric field Ez, earthquake precursors in the form of anomalous negative bays have been found earlier. In some cases, anomalously high sporadic layer Es, interpreted as an ionospheric precursor of an earthquake, was observed simultaneously with anomalous negative bays in Ez. All these cases were correlated with earthquakes of different magnitudes which occurred with a significant time delay (more than five days) after the precursor appearance. Based on the whole data set (including those for simultaneously measured Es and Ez), empirical dependences linking the prediction time of a precursor, earthquake magnitudes, and the distance from the observation point to the epicenter, are presented. It is shown that these dependences are close to those obtained earlier for long-term earthquake precursors in near-surface geophysical fields of the same seismoactive region. Estimates of the prediction time for earthquake precursors on the boundaries of preparation zones are presented.

Orientations of the principal paleostress in the Western Bohemia sesmoactive region and their comparison with the recent stress

The palaeostress analyses based on the fault striae data were carried out in the Western Bohemia seismoactive region. The results of these analyses were compared with the recent orientations of the principal stresses determined from focal mechanisms of micro-earthquakes. The fault striae data were obtained mainly from the late-Variscan granites. No data for the palaeostress analyses were found in the post-Variscan (Tertiary) sedimentary cover.

The problem of the occurrence of neutrons of terrestrial origin during seismic wave travel

The results of experimental measurements of thermal neutrons in 1986–1997 in Pamir, which is one of the most seismoactive regions of the world, are studied. In this period, visible peaks in the thermal neutron flux near the Earth’s surface were found, especially in the periods near the upper and lower transits of the moon during a new moon or full moon, when the tidal gravitational wave reaches its maximum value. Additionally, about 500 earthquakes with m > 4 occurred in the same period of the operation of neutron counters. The time of seismic-wave travel across the given territory was known at a precision of less than 1 min (in some cases). Nevertheless, increases in neutron flux have never been observed during the travel of a seismic wave. Why is this? It appears that the mechanical effect on the Earth’s crust has the same impact with no respect to the cause of this effect; however, this was observed during experiments. This paper studies the reasons for this lack and the probable conditions that are favorable for an increase in terrestrial thermal neutron flux when a seismic wave travels across a territory.

Detailed Study of the Seismic Regime in the Garm Epicenlral Region

The Garni region of the USSR, like California in the USA, is a true earthquake laboratory. Here and there earthquakes not only often occur and reach high intensities, but they are also being systematically studied on the basis of instrumental data. That is why the results obtained in these regions (and in a few other regions of the globe) become to a great extent of general seismological importance. From 1955 on, according to a sufficiently complete program, continuous observations of the seismic regime were carried out in the Garm region. Seismic regime we understand as the entire complex of earthquakes considered in time and space. Into our program the earthquakes with origins in the earth's crust were included. Their seismic energie E (being related to a sphere of a radius B = 10 km surrounding the hypocentre) varying within a range of 1012-1017 joules. The investigations were carried out mainly in the 106-1014 joules range. In studying the energy distribution of the yearly earthquake number N in the Garm region the slope y — — zllog NjA log E of the earthquake occurrence graph N{E) was found to be only slightly varying with time and space (i.e. from one region to another one) notwithstanding the possible essential change in the general seismic activity (Fig. 1). For the Garm region, as seemingly for most seismoactive regions of the globe, this slope is on the average y = 0.43 + 0.05 (Fig. 2). It is of interest to compare these data (as it was done in (2)) with Gutenberg's statistics for the yearly number of shallow earthquakes (with foci in the earth's crust) occuring throughout the globe. Fig. 3

Comparative analyses of the radon and hydrogen fieldes in conditions of the seismoactive and platform regions

Comparative analyses of the radon and hydrogen fieldes in conditions of the seismoactive and platform regions

On the acoustic model of lithosphere-atmosphere-ionosphere coupling before earthquakes

Abstract. In this work, the many-fluid magnetohydrodynamic theory is applied to describe the modification of the electromagnetic field of the ionospheric E-layer by acoustic-type waves. There, altitudinal profiles of the electromagnetic field and the plasma parameters of the atmosphere and ionosphere are taken into account. It is concluded that at E-region altitudes above seismo-active regions, magnetohydrodynamic waves as Alfvén and magnetoacoustic ones might change their amplitude and direction of propagation. Waves of the Farley-Buneman type might also be excited a few days before very strong earthquakes. The collisions between the neutral and charged particles of the E-layer also cause diffusion and heating processes. Thus, changes of the characteristic foE-frequency might be obtained.