Strong Seismic Events Research Articles

Geomagnetic and ionospheric effects two consecutive strong earthquakes in Morocco on september 08, 2023

The geophysical effects of a strong seismic event in the form of two earthquakes of magnitude 6.8 and 4.9 that occurred on September 08, 2023 in Morocco at close times 22:11 and 22:30 UTC with an epicentral distance between the foci of ~ 4 km are considered. We used data from a number of observatories of the INTERMAGNET network and the results of magnetic registration at the Mikhnevo Geophysical Observatory of IDG RAS. It was shown that in the absence of significant global disturbances of the Earth’s magnetic field, earthquakes were accompanied by a series of three positive bay-shaped geomagnetic variations with maximum amplitudes from ~1 to ~10 nT, following each other after ~60 min. The maxima of the induced magnetic field variations were observed almost synchronously at distances from ~800 to ~10000 km. The delay time of the magnetic effect relative to the main shock of the first earthquake was ~70 min. Taking into account the almost planetary nature and high synchronicity of the magnetic field disturbances caused over a significant range of distances, as well as time delays corresponding in order of magnitude to the travel time of the seismic signal of a distance multiple of the size of the Earth, it is suggested that the magnetic effect of the seismic event in question was caused by a global source, which can serve as an excited geodynamo. The ionospheric effect of the seismic event under consideration is presented in the form of variations of the critical frequency f0F2 calculated from the data of the ground-based sounding station of the del Ebre Observatory.

Characterizing the free-vibration response of a two-span rocking bridge with free-standing columns

For accelerated bridge construction (ABC), replacing traditional emulative connections of precast elements with simpler discontinuities may lead to more resilient structures with reduced expected damages after strong seismic events. This paper comprises novel free-vibration tests of a 1:10 scale two-span rocking bridge with free-standing columns with proper geometrical and dynamic similarity. The two spans induced in the model the interaction between frames with different tributary masses, as would be expected for a realistic bridge. To excite the bridge uniformly, the experimental protocol consisted of forty-nine incremental sinusoidal ground motions that were interrupted, letting the bridge vibrate freely to rest. The results were compared with six analytical models. The results showed that the structure remained undamaged for the free-vibration tests after drifts up to 6 % and did not wobble unrestricted. The results were used to obtain the dynamic properties of the system and their variation to displacement increments. Construction imperfections induced the model to rock for all excitations, including low-intensity excitations, and to vibrate with periods different from those of theoretical equations at low displacements. This behavior was critical in the comparison between experimental results and the estimates from analytical models. These findings demonstrate that rocking bridges are a suitable system to control structural damage during seismic events despite the apparent variability of the behavior under realistic conditions. However, the design of these structures must account for the effects of construction imperfections at the rocking surface. The experimental results are openly available for download in the DesignSafe Data Depot using this DOI https://doi.org/10.17603/ds2-znfv-8t55.

Seismic response and damage evolution process of a bedded slope‒tunnel system via the continuum‒discontinuum element method

To investigate the failure evolution process and failure mechanism of the bedded slope‒tunnel system under earthquakes, this work examines a specific layered slope at a tunnel portal in southeast China and conducts a 2D dynamic analysis with the continuum‒discontinuum element method (CDEM). It investigates the slope's dynamic behavior and potential for instability by evaluating the wave patterns, acceleration, displacement, Hilbert‒Huang transform (HHT) spectral analysis, and equivalent crack ratio. The research results indicate that the analysis of acceleration and displacement over time provides insights into wave propagation within a slope. During minor earthquakes (< 0.3 g), the slope experiences dynamic amplification at the surface and elevation-dependent effects, which are less evident during stronger seismic events. This work also revealed a positive correlation between the tunnel's dynamic amplification and elevation. A method leveraging HHT energy analysis, in conjunction with the slope's equivalent fracture ratio, is introduced to trace the progression of seismic damage across temporal and spatial dimensions. The progression of seismic intensity is characterized by stages of local failure initiation, expansion, and eventual holistic failure. Similarly, the temporal dynamics of instability are categorized into phases of initial instability, acceleration, and eventual sliding. Furthermore, this work explores the impact of tunnels on slope stability by comparing the equivalent fracture ratios and dynamic displacement patterns of slopes both with and without tunnels, revealing the evolution process of seismic damage to slope‒tunnel systems. This work provides a reference for the seismic design of complex slope‒tunnel systems.

The Hydrological Impact of Historical and Modern Earthquakes in Central-Southern Italy: Data Analysis and Seismotectonic Insights

Abstract We present the results of research conducted on the hydrological effects induced by historical and modern earthquakes in the central-southern Apennines of Italy. We investigated thirty-nine seismic events of magnitude between M 4.1 and 7.1 that occurred between 1688 and 2020. We collected 526 observations of coseismic and postseismic hydrological effects such as increase or decrease in streamflow, variations in the water levels in wells, formation and/or disappearance of springs and changes in their discharge, and changes in the chemical and physical characteristics of waters. More than half of the observations were new data unpublished to date in the scientific literature. We find that the ease of finding data of interest is strongly influenced by the historical period in which the seismic event occurred. We summarize the methodology of data retrieval and its classification and present examples and maps of coseismic hydrological changes associated with individual seismic events. Most of our novel data derive from seismic postcards, macroseismic questionnaires, and hydrographic annals. However, a nonnegligible set of data comes from a careful rereading of sources—both historical and modern—that were at first considered fruitless. The majority of data concerns an excess flow in streams and springs, and physical–chemical variations such as turbidity, an increase in temperature, and gas emission. We also find that the maximum distance to which seismically induced streamflow responses have been reported can be related to the earthquake magnitude and use this distance to derive an alternative magnitude for some of the strongest earthquakes of our dataset. Finally, we show a potential application of this type of research because the distribution of coseismic hydrological changes can provide constraints in discriminating between the causative faults of strong historical seismic events for which the instrumental data are scarce or not available.

New OpenSees material model for simulating reinforced concrete shear walls subjected to coupled axial tension and cyclic lateral loads

In high-rise buildings, reinforced concrete (RC) shear walls, particularly those forming part of coupled wall systems or core wall systems, may be subjected to coupled axial tension and cyclic lateral loads during strong seismic events. A new two-dimensional material model named the “Fixed Angle Model Considering Crack Sliding” (FAM-CS) was proposed for simulating the nonlinear behavior of RC walls subjected to axial tension and cyclic lateral loads. The proposed model was implemented in the OpenSees platform. Nonlinear constitutive models for shear aggregate interlock effects of concrete and dowel action of rebars were incorporated into the proposed model to represent the shear transfer mechanisms along concrete cracks. The proposed model was validated against the test data of six wall specimens subjected to coupled axial tension and cyclic lateral loads. The results indicated that the proposed model reasonably predicted the lateral strength capacity (an average error of 6.2 %) and the residual strength at the maximum drift loading (an average error of 12.3 %) of the specimens. For comparison, three other commonly used models, the Shear-Flexure Interaction Multiple-Vertical-Line-Element-Model, the multi-layer shell element model and the Cyclic Softened Membrane Model were adopted for the simulation of the specimens. Compared with the three existing OpenSees models, the newly implemented material model provided improved predictions of the wall hysteretic behavior with respect to lateral strength capacity, lateral strength degradation, pinching characteristics and cyclic stiffness degradation. In addition, the proposed model reasonably captured the localized failure pattern as well as the energy dissipation characteristics of the test specimens. Finally, a mesh sensitivity study was conducted to assess the robustness of the proposed model. The results revealed that the proposed model was robust regarding the lateral load-drift responses of RC walls, with a mesh size ranging from approximately one to three times the average crack spacing.

Seismic variations before Eastern Anatolian catastrophic events in February 2023

AbstractThe East Anatolian Fault System has been intensively studied over the years due to its potential to generate strong earthquakes and the high exposure of the economy and population in the region. This interest intensified even more after the strong earthquakes in the area at the beginning of February 2023, leading to a focused search for features and precursors that might suggest such an upcoming event. We analyze certain characteristics of seismicity within the East Anatolian Fault System before the earthquakes of February 6, 2023, with magnitudes Mw = 7.8 and Mw = 7.5, over the time period between 1983 and 2022. The earthquake catalog from January 1983 to September 2023, created by Turkish Bogazici University KOERI, is used. Processing of the data is performed by the ZMAP 7.1 software used in the MATLAB environment. Events with a magnitude greater than 2.5 are considered in four time periods: 1983–1992, 1993–2002, 2003–2012, and 2013–2022, totaling 29,346 events. The b-value of the magnitude-frequency distribution of earthquakes (slope of the recurrence graph) is determined; the parameter β, indicative of the increase or decrease in the rate of anomalous seismicity, and parameter Z, associated with anomalous seismic quiescence, is evaluated. A significant decrease in the value of b (from 1.07 to 0.84) is observed when comparing the two periods (2013–2017/2018–2022), indicating accumulated stress in the Earth’s crust. Furthermore, the Z parameter analysis for the period July 2021 to December 2022 shows evidence of relative seismic quiet in the examined area compared to the period from January 2020 to the end of June 2021. Those results suggest that the spatiotemporal variations of the studied seismic parameters could serve as predictors of the two very strong seismic events in the southern part of the Eastern Anatolian region of Turkey.

Experimental and finite element assessment of stabilizing configurations for underground heritage sites

Heritage sites in Alexandria, Egypt, are some of the UNESCO world heritage sites at high risk from geo-environmental hazards, in particular caused by sea level rise and heavy rain due to the climate change. Recently, safeguarding UNESCO world subterranean and built heritage draws more attention. After recent environmental catastrophies in Alexandria, sustainable conservation materials and stabilizing configurations of underground monumental structures has also become urgent and highly demanded. Based on typical damage due to the heavy weathering caused by the ground water table and salt, this paper offers a guide for engineers and conservators, where rock structures consolidation and stabilizing configurations to protect these structures in the static state and against strong seismic events is presented. In this paper, typical geotechnical problems and damage to the Catacombs of of Kom El-Shoqafa are presented first, followed by an experimental evaluation methodology that includes spectroscopic and morphological characterization in addition to the mechanical testing of untreated and treated rock samples with synthetic organosilicone and acrylic compounds. The effectiveness of the new silica-based consolidants was evaluated in terms of the amount of solid adsorbed, mechanical properties (e.g., surface hardness, ultrasonic velocity, modulus of elasticity and modulus of compressive strength), and resistance to salt crystallization. The treated groups showed better mechanical strength than the control group. The ability of the treated samples to resist climate change negative impact was also greatly improved. According to laboratory tests, new silica-based hardeners and hydrophobic materials have great potential for strengthening weathered Calcarenitic rock structures. It was observed that the rock samples containing the modified binder (MTMOS + Wacher BS 15) reach higher mechanical strength parameters. After the experimental study (testing procedures), FEM analysis was performed using PLAXIS 2D code to validate the silica-based consolidants and verify their efficiency in improving the response of rock structures in static and seismic states against strong earthquake events. The results of this work confirm the high potential of low-cost injection techniques and stabilizing configurations (pre- stressed anchors and concrete friction piles) technology, confirming the possibility of achieving significant improvement in the geotechnical properties of Calcarenitic rock structures and enhancing the seismic performance of underground archaeological structures using low-cost injection technology that is easy to manufacture.

Advancing the understanding of earthquake risk in Portugal

The assessment of earthquake risk at the national scale is crucial for the design and implementation of risk reduction measures. Due to its location in the southwest of the Eurasian plate, Portugal is exposed to moderate to strong seismic events, such as the well-known 1755 Lisbon earthquake. We reviewed existing studies covering exposure, seismic hazard, vulnerability, and risk assessment for Portugal, and performed probabilistic seismic hazard and risk analyses for the country using new model components. These include a new exposure model developed for the residential building stock using the 2021 national Building Census Survey, a recent exposure model for commercial and industrial buildings, updated vulnerability functions for 116 building classes, and the recently released European Probabilistic Seismic Hazard model. The seismic risk results include average annual economic losses, fatalities, buildings with complete damage, and population left homeless. These results allowed the identification of the regions in Portugal with the highest earthquake risk, as well as which building classes contribute the most to the overall impact.

Shake table tests of steel moment resisting frame with self‐centering SMA‐based isolators

AbstractThis paper investigates a steel moment resisting frame (MRF) with a novel type of self‐centering (SC) base isolators, wherein superelastic shape memory alloy (SMA) U‐shaped dampers (SMAUDs) work as core components. A two‐story steel MRF model equipped with two SMAUD‐based isolators was designed and built in the laboratory, and a series of shake table tests were conducted to examine the dynamic behavior and seismic performance of the frame. Throughout all the tests, no interventions, such as repair or replacement of frame or isolator members, were done. Shake table test results demonstrated that the SMAUD‐based isolators could withstand multiple strong earthquakes with stable SC behavior. The utilization of SMAUD‐based isolators provided effective protection for the frame, enabling it to restore its original position with minimal structural damage. A numerical model of the tested steel MRF with SMAUD‐based isolators was also built. The results obtained from the numerical analyses agreed with those of the shake table tests satisfactorily. A comparative study of the seismic performance between the MRF with SMAUD‐based isolators and the MRF with traditional steel U‐shaped damper‐based isolators was also conducted in the shake table tests. The results showed that SMAUD‐based isolators not only inherit the isolation function of conventional isolators to protect the frame but also possess an SC ability to eliminate residual isolator deformation effectively. Moreover, SMAUD‐based isolators demonstrate remarkable resilience to withstand multiple strong seismic events without any need for repair or replacement.

Wavelet-based correlations of the global magnetic field in connection to strongest earthquakes

We consider 3-component records of the magnetic field strength with a time step of 1 min at 153 stations of the INTERMAGNET network for 31 years, 1991–2021. Data analysis is based on the calculation of pairwise correlation coefficients between wavelet coefficients in successive time windows 1 day long (1440 min counts). To describe the state of the magnetic field, the maxima of the average values of all pairwise correlation coefficients between stations were chosen, calculated over all detail levels of the wavelet decomposition and over all components of the magnetic field strength vector. The daily time series of such maxima is called wavelet correlation. The division of the network stations into 7 clusters is considered, and a time series of wavelet correlations is calculated for each cluster. In a sliding time window with a length of 365 days, correlation measures of synchronization of wavelet correlations from different clusters are calculated, which are compared with the strongest earthquakes with a magnitude of at least 8.5. For the global time series of wavelet correlations, the method of influence matrices is used to study the relationship between the maximum correlation responses to a change in the length of the day and a sequence of earthquakes with a magnitude of at least 7. As a result of the analysis, precursor effects are identified, and the important role of the Maule earthquake in Chile on February 27, 2010 in the behavior of the response of magnetic field for the preparation of strong seismic events is shown.

Predicting Peak Ground Acceleration of Strong-Motion Earthquakes Using Variable Snapshots of P-Wave Data with Long Short-Term Memory Neural Network

Abstract Conventional earthquake early warning systems (EEWS) rely on mathematical functions that utilize P-wave parameters extracted over a 3 s window to estimate peak ground acceleration (PGA). Advancements in the capabilities of deep neural networks to approximate universal functions, coupled with the availability of strong seismic event data, offer an unprecedented opportunity to evaluate the relationship between variable snapshots of P-wave data and the PGA of strong-motion earthquakes. This convergence of technology and data opens new avenues for research into utilizing smaller snapshots of P-wave in EEWS. Our study centers on the utilization of a long short-term memory (LSTM) neural network to model long dependencies within the P-wave of 1839 earthquakes recorded by the Kiyonshin Network (K-NET) for the prediction of PGA of S waves. Our methodology involves experiments that ultimately evaluate the network’s performance on 4, 3, and 2 s of P-wave snapshots. Our findings indicate that there is sufficient information in 2 s of temporal accelerometer readings after the onset of P waves to predict PGA accurately with an LSTM network.

Investigating a Possible Correlation between NOAA-Satellite-Detected Electron Precipitations and South Pacific Tectonic Events

On 4 March 2021, a devastating M8.1 earthquake struck the Kermadec Islands of New Zealand. Given the tremendous energy released during the event, we sought to investigate the event’s potential impact on the ionosphere and the inner Van Allen Belt using data from the high-energy electron detectors on board the NOAA-18 satellite. The survey was also extended to the strongest shallow M6.5+ earthquakes occurring between 150° and 190° in longitude, and between −5° and −35° in latitude over the previous ten years. In nearly all cases, evident electron fluxes entering the loss cone were observed. To explore the possibility of a connection between ionospheric signals and tectonic events in this intensely active region, we analyzed electron losses from the inner Van Allen Belt, taking into account latitude, longitude, day/night times, and proximity to the South Atlantic Anomaly. Compared to previous studies, here only the most significant loss phenomena persistent in the ionosphere were considered. Particular interest was reserved for the intense electron loss events that had a duration spanning from a few to several minutes and occurred several hours before and after strong seismic events. Thereafter, time series of electron counting rates and strong Southern Pacific earthquakes were transformed into binary series, and the series multiplication was investigated. The results suggest four peaks of association, including a first couple between electron perturbations detected for ascending semi-orbits and seismic events and a second one between electron perturbations detected in the southern ionosphere and seismic events. They both anticipated the occurrence of earthquakes, occurring around 4 h before them. Other couples were observed between electron perturbations detected for descending semi-orbits and seismic events and between electron perturbations detected in the northern ionosphere and seismic events. They both occurred around 3 h after the occurrence of earthquakes. The case of perturbations anticipating seismic events has the intriguing properties of sustaining the hypothesis that a physical interaction occurred around 6 h before seismic events as in the West Pacific case. A physical model of electrons detected far several thousands of km from the earthquake epicenters was also presented. However, a simulation of random seismic events suggested that the null hypothesis cannot be fully rejected for these associations, prompting many more analyses and case studies.

Cross-Correlation among Seismic Events, Rainfalls, and Carbon Dioxide Anomalies in Spring Water: Insights from Geochemical Monitoring in Northern Tuscany, Italy

Variations in the CO2 dissolved in water springs have long been observed near the epicenters of moderate and strong earthquakes. In a recent work focused on data collected during the 2017–2021 period from a monitoring site in the Northern Apennines, Italy, we noticed a significant correlation between CO2 anomalies and moderate-to-weak seismic activity. Here, we extended this analysis by focusing on data collected from the same site during a different period (2010–2013) and by integrating the CENSUS method with an artificial neural network (ANN) in the already-tested protocol. As in our previous work, a fit of the computed residual CO2 distributions allowed us to evidence statistically relevant CO2 anomalies. Thus, we extended a test of the linear dependence of these anomalies to seismic events over a longer period by means of binary correlations. This new analysis also included strong seismic events. Depending on the method applied, we observed different time lags. Specifically, using the CENSUS methodology, we detected a CO2 anomaly one day ahead of the earthquake and another anomaly eleven days ahead. However, no anomaly was observed with the ANN methodology. We also investigated possible correlations between CO2 concentrations and rain events and between rain events and earthquakes, highlighting the occurrence of a CO2 anomaly one day after a rain event of at least 10 mm and no linear dependence of seismic and rain events. Similar to our previous work, we achieved a probability gain of around 4, which is the probably of earthquake increases after CO2 anomaly observations.

DEFORMATION INTERACTION OF STRONG EARTHQUAKES OF 2010–2016 IN THE ZONE OF INFLUENCE OF THE HIKURANGA SUPERPLUME (NEW ZEALAND) ACCORDING TO GPS OBSERVATIONS

Between 2010 and 2016, a series of 11 strong M&gt;6 earthquakes occurred in New Zealand. In the area covering the epicentral zones of these seismic events, the spatiotemporal characteristics of movements and deformations of the Earth’s crust were obtained based on the processing of continuous satellite GPS observations at 64 points of the geodetic network. Using these data, we have studied the evolution of horizontal movements and deformations in order to reveal the possible relationship between the observed deformational and seismic processes. Analysis has been made on the total shear deformation, since the main tectonic structures of the region are faults with a shear mechanism of displacement of their sides. The presence of a giant mantle superplume in the area was the reason for the study of the behavior of horizontal dilatation deformation, and horizontal and vertical crustal motions. Based on the obtained digital deformation models, there were created kinematic visualizations, which are synoptic animations providing direct observations of the seismic deformation process and their heuristic analysis. The study revealed that a series of the strongest earthquakes may be interconnected by a long-term single deformation process, which is caused by the occurrence of an anomalous total shear deformation. The general maximum of shear deformation, dilatation deformation, and horizontal and vertical displacements are concentrated in the center of mantle superplume activity. Prior to strong seismic events, there occur zones of deficit (minimum) displacements of the Earth’s crust in the area of future epicenters, which is of research interest in terms of predicting their locations.

What Is the Effect of Seismic Swarms on Short-Term Seismic Hazard and Gutenberg-Richter b-Value Temporal Variation? Examples from Central Italy, October–November 2023

A seismic hazard can be quantified by using probabilities. Modern seismic forecasting models (e.g., Operational Earthquake Forecasting systems) allow us to quantify the short-term variations in such probabilities. Indeed these probabilities change with time and space, in particular after strong seismic events. However, the short-term seismic hazard could also change during seismic swarms, i.e., a sequence with several small-/medium-sized events. The goal of this work is to quantify these changes, using the Italian Operational Earthquake Forecasting system, and also estimate the variations in the Gutenberg–Richter b-value. We focus our attention on three seismic swarms that occurred in Central Italy in October–November 2023. Our results indicate that short-term variations in seismic hazard are limited, less than an order of magnitude, and also that b-value variations are not significant. Placing our findings in a more general context, we can state that according to currently available models and catalogs, the occurrence of seismic swarms does not significantly affect the short-term seismic hazard.

Tectonics and Seismicity of the Lunar South Polar Region

The lunar south pole regions are subjected to global stresses that result in contractional deformation and associated seismicity. This deformation is mainly expressed by lobate thrust fault scarps; examples are globally distributed, including polar regions. One small cluster of lobate scarps falls within the de Gerlache Rim 2 Artemis III candidate landing region. The formation of the largest de Gerlache scarp, less than 60 km from the pole, may have been the source of one of the strongest shallow moonquakes recorded by the Apollo Passive Seismic Network. The scarp is within a probabilistic space of relocated epicenters for this event determined in a previous study. Modeling suggests that a shallow moonquake with an M w of ∼5.3 may have formed the lobate thrust fault scarp. We modeled the peak ground acceleration generated by such an event and found that strong to moderate ground shaking is predicted at a distance from the source of at least ∼40 km, while moderate to light shaking may extend beyond ∼50 km. Models of the slope stability in the south polar region predict that most of the steep slopes in Shackleton crater are susceptible to regolith landslides. Light seismic shaking may be all that is necessary to trigger regolith landslides, particularly if the regolith has low cohesion (on the order of ∼0.1 kPa). The potential of strong seismic events from active thrust faults should be considered when preparing and locating permanent outposts and pose a possible hazard to future robotic and human exploration of the south polar region.

A model of TEC perturbations possibly related to seismic activity

For application of observed anomalies of the total electron content (TEC) in the ionosphere for short-term earthquake prediction, it is necessary to understand the physical nature of such anomalies during the preparation of a strong seismic event. The physical mechanism of occurrence of such anomalies is considered in order to distinguish the TEC disturbance of a seismic origin and to clear the processes in the lithosphere resulted in an appearance of the TEC anomaly in the ionosphere. It is supposed that the observed TEC anomalies arise as a result of occurrence of additional electric field in the ionosphere demonstrated by numerous satellite data before the impending earthquakes. At the same time, an injection of charged aerosols into the atmosphere in the epicentral earthquake area was detected. As a result, an electromotive force arises in the surface layer of the atmosphere, which initiates a perturbation of the electric current in the global circuit and the electric field appearance in the ionosphere. We have shown that the TEC disturbance arises as a result of the heating of the ionosphere by electric current and the plasma drift in the electric field of this current. The spatial distribution of TEC arises as a result of the combined action of these two factors, and its nature depends on the relationship between them. Based on the developed model the numerical study of the spatial distribution of TEC in the ionosphere is possible for a given horizontal distribution of the concentration of charged aerosols in the atmosphere near the Earth’s surface.

MONITORING OF CHANGES IN THE STRESS-STRAIN STATE OF GEOENVIRONMENT AT THE PETROPAVLOVSK GEODYNAMIC TESTING SITE BASED ON THE MULTI-INSTRUMENTAL BOREHOLE AND GPS DATA DURING THE ACTIVE PHASE OF PREPARING THE ZHUPANOVSKY EARTHQUAKE (JANUARY 30, 2016, Mw 7.2)

The paper presents the results of comparative analysis of the data regarding the multi-instrumental borehole monitoring data of changes in the geoenvironment stress-strain state and GPS data obtained in the time vicinity of the close strong Zhupanovsky earthquake. The purpose this study was to assess the feasibility of using GPS measurements on routine basis for effective monitoring of strong Kamchatka earthquakes in the area of Petropavlovsk-Kamchatsky. The Zhupanovsky earthquake active phase was chosen as a "test" time interval for comparing GPS and borehole monitoring data. This earthquake has been the strongest seismic event since 2000 in terms of the ratio of the earthquake focus length to the hypocentral distance. The time series borehole electromagnetic and geoacoustic data were compared with the dilatation series reflecting the relative changes in the area of a triangle composed of Kamchatka GPS observation network located in the Petropavlovsk geodynamic testing site. The analysis indicates a high degree of consistency in these time series. GPS data obtained during the active phase of the earthquake preparation is agree with the results of mathematical modeling expected values of volumetric strain on the daylight surface on the eve of the earthquake. A joint analysis of borehole and GPS data made it possible to specify the time limits for the stages of change in the stress-strain state of geoenvironment and to resolve ambiguity of interpretation of the electromagnetic and geoacoustic borehole measurement results at the final stage of preparing the Zhupanovsky earthquake.

SARIKHOSOR EARTHQUAKES on March 29, 2018 with KR=13.1, Мs=5.1, I0=6 and March 7, 2019 with KR=12.1, МS=4.1, I0=5–6 (Tajikistan)

General information about the tangible earthquakes that occurred on the territory of Tajikistan in 2018–2019 and their confinement to tectonic structures is given. The most active tectonic structures during this period within which strong seismic events occurred are determined. The results of a survey of macroseismic manifestations of March 29, 2018 and March 7, 2019 earthquakes, which occurred in the eastern part of the Tajik depression, and their isoseist maps are presented. An assumption about the possible influence of two large reservoirs on the increase of the seismicity of the region is made. An analysis of the depths of earthquake sources in comparison with the geological and tectonic structures of the region is made. The difference in the depths of earthquakes, determined by different seismological services, makes it difficult to link the source of seismic events to tectonic structures and to determine their parameters.

Influence of Lower Lateral Bracing on the Seismic Pounding Damage to Slab-On-Girder Steel Bridges

During strong seismic events, seismic-induced pounding has been observed to cause damage to bridges. Previous studies on seismic-induced bridge pounding responses have generally focused on reinforced concrete bridges. However, the seismic damage between steel and reinforced concrete beams is significantly different, and research on steel beams’ seismic pounding response remains limited. Therefore, this paper adopts the multiscale fine three-dimensional numerical simulation method to study the seismic response of a slab-on-girder steel bridge. The numerical results show that the lower lateral bracing has a significant effect on seismic damage to steel beams. The lower lateral bracing can share about 1/3 of the pounding action and reduce the displacement angle of the steel beam by 40%. Under horizontal two-way seismic action, the lower lateral bracing significantly reduces the stress on the steel beam. In addition, the bracing should have continuous stiffeners to avoid connection failure. Generally, the lower lateral bracing should be considered in the design of the slab-on-girder steel bridge. It significantly improves the lateral seismic performance of the bridge and reduces seismic damage to steel beams.