Search Results (6,032)

Laboratory acoustic emissions (AEs) serve as small-scale analogues to earthquakes, offering fundamental insights into seismic processes. To ensure accurate physical interpretations of AEs, rigorous calibration of the acoustic system is essential. In this paper, we present an empirical calibration technique that quantifies sensor response, instrumentation effects, and path characteristics into a single entity termed instrument apparatus response. Using a controlled seismic source with different steel balls, we retrieve the instrument apparatus response in the frequency domain under typical experimental conditions for various piezoelectric sensors (PZTs) arranged to simulate a three-component seismic station. Removing these responses from the raw AE spectra allows us to obtain calibrated AE source spectra, which are then effectively used to constrain the seismic AE source parameters. We apply this calibration method to acoustic emissions (AEs) generated during unstable stick-slip behavior of a quartz gouge in double direct shear experiments. The calibrated AEs range in magnitude from −7.1 to −6.4 and exhibit stress drops between 0.075 MPa and 4.29 MPa, consistent with earthquake scaling relation. This result highlights the strong similarities between AEs generated from frictional gouge experiments and natural earthquakes. Through this acoustic emission calibration, we gain physical insights into the seismic sources of laboratory AEs, enhancing our understanding of seismic rupture processes in fault gouge experiments. Full article

A high-resolution seismic survey (HRSS) is often used in coal exploration to bridge the data gap between two consecutive boreholes and avoid ambiguity in geological interpretation. The application of high-resolution seismic surveys in the Indian context is challenging as the delineation of thin non-coal layers within the coal layer requires a very high seismic data resolution. However, conventional seismic processing techniques fail to resolve thin coal/non-coal layers and faults, which is crucial for the precise estimation of coal resources and mine economics. To address these issues, we applied the inverse continuous wavelet transform deconvolution (ICWT-Decon) technique to post-stack depth-migrated seismic sections. We examined the feasibility of the ICWT-Decon technique in both a synthetic post-stack depth-migrated model and 2D/3D seismic data from the North Karanpura and Talcher Coalfields in Eastern India. The results offered enhanced seismic sections, attributes (similarity and sweetness), and acoustic inversion that aided in the precise positioning of faults and the delineation of a thin non-coal layer of 4.68 m within a 16.7 m coal seam at an approximate depth of 450 m to 550 m. This helped in the refinement of the resource estimation from 74.96 MT before applying ICWT-Decon to 55.92 MT afterward. Overall, the results of the study showed enhancements in the seismic data resolution, the better output of seismic attributes, and acoustic inversion, which could enable more precise lithological and structural interpretation. Full article

Shape memory alloys (SMAs) have emerged as promising materials for self-centering seismic applications due to their unique properties of superelasticity and shape memory effect. This review article examines recent advancements in the use of SMAs for self-centering seismic devices, focusing on their mechanical properties, damping characteristics and applications in structural engineering. The fundamental principles of SMAs are discussed, including their phase transformations and hysteretic behavior, and their performance under various loading conditions is analyzed. The article also explores different SMA-based damping systems, with a particular emphasis on innovative self-centering friction dampers. Furthermore, the influence of factors such as alloy composition, heat treatment and loading parameters on the seismic performance of SMA devices is investigated. The review concludes by highlighting the potential of SMAs in improving the seismic resilience of structures and identifying future research directions in this field. Full article

A hysteretic model is essential for the study of the seismic performance of structures. Due to the ability to capture the component strength and stiffness deterioration, the modified Ibarra–Medina–Krawinkler (ModIMK) hysteretic model has been widely used recently. Previous studies on the ModIMK model have mainly focused on reinforced-concrete (RC) square columns, and very few have focused on circular columns. In contrast, studies on the ModIMK model specifically for corroded circular RC columns have not yet been conducted. For this reason, a database of 35 corroded and uncorroded comparison columns was gathered, and the hysteretic model parameters of each column were calibrated. The ratios of the model parameters of the corroded and uncorroded comparison components are defined as the corrosion-induced deterioration coefficients (CIDCs). After the CIDCs were calculated for all the corroded columns, the empirical equations for the CIDCs were established using regression methods. Through determining the ModIMK model parameters of the corroded columns when they were uncorroded, combined with these equations, the ModIMK model parameters of the corroded circular columns were calculated and their hysteretic models defined. Finally, the accuracy of the ModIMK model’s prediction method was demonstrated using the hysteretic response analyses of four components in the database and the application of two components outside the database. The prediction method lays the foundation for applying the ModIMK model to structures containing corroded circular RC columns. Full article

Determining the impact of pulse-type earthquake characteristics on the vulnerability of base-isolated buildings under non-pounding conditions has yielded conflicting results in previous studies. Moreover, this issue has received less attention for pounding conditions, especially floor-to-floor pounding. Therefore, this study aims to investigate the correlation between pulse-type earthquake characteristics and the seismic response of buildings under both pounding and non-pounding conditions. In the first stage, three base-isolated buildings and one fixed-base building are analyzed separately under 40 pulse-type earthquakes using the nonlinear time history method. Three scenarios are then considered to account for pounding with adjacent buildings. In the first pounding scenario, a base-isolated building with an intermediate moment frame (IMF) is placed between two fixed-base buildings. The second scenario involves changing the base-isolated building’s superstructure system to a special moment frame (SMF). Finally, the third scenario increases the base isolation period (T_b) of the base-isolated building used in scenario two. The correlation between earthquake characteristics and the seismic response of buildings is assessed by linear regression and the Pearson correlation coefficient. The results demonstrate that peak ground acceleration (PGA) has a strong correlation with the seismic response of buildings under pounding conditions, while peak ground velocity (PGV) shows a stronger correlation under non-pounding conditions. However, predicting building vulnerability with a single pulse-type earthquake characteristic remains unreliable unless a large number of ground motions are considered. Otherwise, it is crucial to consider the correlation of all earthquake characteristics with seismic responses. Full article

Maseve Mine is located in the western limb of the Bushveld Complex, recognized as the largest layered igneous intrusion in the world. The study shows results from surface (SP1, SP2, and SP3) and tunnel (T3a, T3b, and TP4b) reflection seismic profiles, totaling 4150 m. Tunnel seismic data were acquired using a seismic landstreamer and spiked geophones with 5 m receiver and shot spacing, as well as a sledgehammer for shots due to space constraints and safety. The profiles, 10–50 m above mineral deposits, crossed major geological structures. Surface seismic profiles used cabled systems and wireless sensors with 5 m and 10 m receiver spacing, respectively, and a 500 kg drop hammer as a source with 10 m shot spacing. Despite high noise levels from mine infrastructure and power cables, a careful processing workflow enhanced target reflections. Interpretation was constrained using borehole data, geological models, and 2D/3D seismic modeling. The processed data exhibit gently dipping reflections associated with faults and dykes, imaging the target mineralization (Merensky Reef and Upper Group 2) and a possible extension. Tunnel seismic experiments demonstrated the application of seismic methods using in-mine infrastructure, while surface experiments proved efficient, illustrating small-scale seismic surveys’ capability to image the subsurface, adding value in active mining environments for exploration with cost-effective seismic equipment. Full article

As a crucial reserve for natural gas, the safe operation of underground gas storage facilities is paramount for seasonal peak shaving and emergency supply security. Focusing on the Lei X gas storage facility in the Liaohe Basin of China, this study delves into the mechanical integrity of gas storage facilities and assesses the upper limit pressure for safe operation. Leveraging seismic logging data, we conducted an analysis and statistical evaluation of boundary faults and top cover characteristics, integrating regional stress fields and rock mechanics to evaluate fault activation pressure and cover failure risk using a fault activation pressure assessment method. This research elucidates the maximum safe operating pressure for underground gas storage facilities. The research findings suggest that the sealing layer of the Lei X gas storage reservoir exhibits a predominant hydro-fracturing pattern. Under the existing stress field conditions, the sealing layer demonstrates favorable sealing properties, and the boundary faults remain relatively stable. Moreover, through data extraction and quantitative analysis, this study clearly determined the critical pressure at which each fault is activated and the pressure at which the sealing layer undergoes hydro-fracturing during cyclic injection and the production of gas storage. Considering the activation pressure and fracturing pressure data for the sealing layer, a secure operating pressure of 15.0 MPa was calculated for gas storage operations. This study offers crucial theoretical support for enhancing injection and production efficiency, as well as ensuring the safe operation of Lei X gas storage and providing technical guidance for future adjustments to injection and production schemes. Full article

This study addresses the potential of machine learning (ML) algorithms in geophysical and geodetic research, particularly for enhancing GNSS time series analysis. We employed XGBoost and Long Short-Term Memory (LSTM) networks to analyze GNSS time series data from the tectonically active Anatolian region. The primary objective was to detect discontinuities associated with seismic events. Using over 13 years of daily data from 15 GNSS stations, our analysis was conducted in two main steps. First, we characterized the signals by identifying linear trends and seasonal variations, achieving $R^2$ values of 0.84 for the XGBoost v.2.1.0 model and 0.81 for the LSTM model. Next, we focused on the residual signals, which are primarily related to tectonic movements. We applied various threshold values and tested different hyperparameters to identify the best-fitting models. We designed a confusion matrix to evaluate and classify the performance of our models. Both XGBoost and LSTM demonstrated robust performance, with XGBoost showing higher true positive rates, indicating its superior ability to detect precise discontinuities. Conversely, LSTM exhibited a lower false positive rate, highlighting its precision in minimizing false alarms. Our findings indicate that the best fitting models for both methods are capable of detecting seismic events (Mw ≥ 4.0) with approximately 85% precision. Full article

Marine sand, in addition to oil and gas resources, is the second-largest marine mineral resource. The rational development and utilization of marine sand resources are conducive to the growth of the marine economy. In the process of marketing marine sand in China, local authorities are required to delineate auctioned sand mining areas after a general survey, commonly referred to as preliminary exploration. Marine sand can be categorized into surface marine sand and buried marine sand. Buried marine sand deposits are buried beneath the sea floor, making it challenging to locate them due to their thin thickness. Consequently, there exist numerous technical difficulties associated with marine sand exploration. We conducted the preliminary research work in the waters off Guangdong Province of the South China Sea, employing a reduced drilling and identifying a potentially extensive deposit of marine sand ore. In this study, various geophysical methods such as sub-bottom profile survey, single-channel seismic survey, and drilling engineering were employed in the northern offshore waters of the South China Sea. As a result, two distinct marine sand bodies were delineated within the study area. Additionally, five reflective interfaces (R₁, R₂, R₃, R₄, and R₅) were identified from top to bottom. These interfaces can be divided into five seismic sequences: A₁, B₁, C₁, D₁, and E₁, respectively. Three sets of strata were recognized: the Holocene Marine facies sediment layer (Q₄^m), the Pleistocene alluvial and pluvial facies sediment layer (Q₃^al+pl), as well as the Pleistocene Marine facies sedimentary layer (Q₃^m). In total, two placers containing marine sand have been discovered during this study. We estimated the volume of marine sand and achieved highly favorable results of the concept that we are proposing a geologic exploration approach that does not involve any previous outcropping analogue study. Full article

Medium-steep bedding rock slopes (MBRSs) are generally considered relatively stable, because the dip angle of the rock layers (45–55°) is larger than the slope angle (40–45°). However, the stability of MBRSs was significantly impacted during the 1933 Diexi earthquake, leading to slope instability. Field investigations revealed that no continuous sliding surface was recognized in the failure slopes. Instead, the source areas of landslides present a “reverse steps” feature, where the step surfaces are perpendicular to the bedding surface, and their normal directions point towards the crest of the slopes. These orientations of “reverse steps” differ significantly from those of steps formed under static conditions, which makes it difficult to explain the phenomenon using traditional failure mechanism of the slope. Therefore, a large-scale shaking table test was conducted to replicate the deformation and failure processes of MBRSs under seismic action. The test revealed the elevation amplification effect, where the amplification factors of the acceleration increased with increasing elevation. As the amplitude of the input seismic wave increased, the acceleration amplification factor initially rose and subsequently decreased with the increase in the shear strain of the rock mass. The dynamic response of the slope under Z-direction seismic waves is stronger than that under X-direction seismic waves. The deformation and failure were mainly concentrated in the upper part of the slope, which was in good agreement with the field observations. Based on these findings, the deformation and failure mechanism of MBRSs was analyzed by considering both the spatial relationship between the seismogenic fault and the slope, and the propagation characteristics of seismic waves along the slope. The seismic failure mode of MBRSs in the study area was characterized as flexural–tensile failure. This work can provide a reference for post-earthquake disaster investigation, as well as disaster prevention and mitigation, in seismically active regions. Full article

Geological reservoirs are widely used for storing or disposing of various fluids and gases, including groundwater, wastewater, carbon dioxide, air, gas, and hydrogen. Monitoring these sites is essential due to the stored assets’ economic value and the disposed materials’ hazardous nature. Reservoir pressure monitoring is vital for ensuring operational success and detecting integrity issues, but it presents challenges due to the difficulty of obtaining comprehensive pressure distribution data. While direct pressure measurement methods are costly and localized, indirect techniques offer a viable alternative, such as inferring reservoir pressure from surface deformation data. This inversion approach integrates a forward model that links pressure distribution to deformation with an optimization algorithm to account for the ill-posed nature of the inversion. The application of forward models for predicting subsidence, uplift, and seismicity is well-established, but using deformation data for monitoring underground activity through inversion has yet to be explored. Previous studies have used various analytical, semi-analytical, and numerical models integrated with optimization tools to perform efficient inversions. However, analytical or semi-analytical solutions are impractical for complex reservoirs, and advanced numerical models are computationally expensive. These studies often rely on prior information, which may only sometimes be available, highlighting the need for innovative approaches. This study addresses these challenges by leveraging advanced numerical models and genetic algorithms to estimate pressure distribution from surface deformation data without needing prior information. The forward model is based on a discrete Green matrix constructed by integrating the finite element method with Python scripting. This matrix encapsulates the influence of reservoir properties and geometry on the displacement field, allowing for the rapid evaluation of displacement due to arbitrary pressure distributions. Precomputing Green’s matrix reduces computational load, making it feasible to apply advanced optimization methods like GA, which are effective for solving ill-posed problems with fewer observation points than unknown parameters. Testing on complex reservoir cases with synthetic data showed less than 5% error in predicted pressure distribution, demonstrating the approach’s reliability. Full article

In landfill cover, geosynthetic packages are often used to fulfil different and simultaneous functions: drainage, waterproofing, separation, reinforcement, and soil protection. In this regard, various types of geosynthetics are combined in succession to allow for water and biogas drainage and to waterproof, reinforce, and provide protection from erosion over the useful lifetime, ranging over many decades if we consider the long phases of disposal, closure, and quiescence of the landfill itself. The creation of the composite cover barrier requires the evaluation of various interfaces’ frictional strength under low contact stresses, both in static and seismic cases. The main purpose of this study is to summarize the results of past laboratory tests carried out on different geosynthetic–geosynthetic and geosynthetic–soil–geosynthetic interfaces using experimental instrumentation developed at the geotechnical laboratory of the University of Padua, which allows for the characterization of the interface geosynthetic friction at low contact stresses. The main aspects highlighted are the kinematic mode of failure, the wearing of the contact surfaces, the presence or absence of interstitial fluid, and, finally, the density level of the granular soil in contact with the geosynthetics. Full article

In this study, we aimed to assess the capacity of a physics-based earthquake simulator to improve our understanding of the seismogenic process. In this respect, we applied a previously tested earthquake simulator to two well-known and completely different seismogenic fault systems, namely the Italian Apennines and the Nankai subduction in Japan, for which long historical records of strong earthquakes are available. They are characterized by different fault mechanisms, fault sizes, and slip rates. Because of the difference in slip rates, the time scale of the seismicity patterns is different for the two systems (several hundreds of years for the Apennines and a few tens of years for the Nankai Fault). The results of simulations that produced synthetic catalogues of 100,000 years show these significant long-term seismicity patterns characterizing the seismic cycles for both seismogenic areas as follows: The average stress and the occurrence rate of earthquakes increase in the long term as the next major earthquake approaches; while the average stress increases uniformly, the occurrence rate stops increasing well in advance of the mainshocks; the b-value exhibits a long-term increase before major earthquakes and a fast decrease shortly before the mainshocks. Even if no specific statistical tool was applied for the quantification of the similarities between the seismicity patterns of the two seismic areas, such similarities are clearly justified by the large number of seismic cycles included in the 100,000-year synthetic catalogues. The paper includes a discussion on the capability of the simulation algorithm to reliably represent the real long-term seismogenic process. This question is difficult to answer because the available historical observations are of too short a duration to provide significant statistical results. In spite of the limitations characterizing the use of earthquake simulators for time-dependent earthquake hazard assessment, and the lack of convincing mechanistic explanations of the specific seismic patterns reproduced by our simulator algorithm, our results encourage further investigations into the application of simulators for the development of seismogenic models, including short-term features. Full article

This study introduces an alternative approach to the assessment of the earthquake resistance of existing buildings and the evaluation of the requirements for seismic retrofit through external stiffening. Instead of assessing individual structural components, we evaluate the entire building using a nonlinear static pushover analysis. Earthquake resistance of the building is defined as a ratio between the total energy that the existing structure can absorb and the energy at its ideal (upgraded) state estimated using the capacity curves obtained from the pushover analysis. The required retrofitting can then be assessed as the stiffness needed to be added to achieve the desired resistance. The study establishes the definition for the ideal capacity of an existing structure, safe displacement limits, and a procedure for deriving the target capacity curves and earthquake-resistance factors. The proposed procedure is applied to a benchmark example, demonstrating that upgrading sub-standard RC structures can be achieved by adding external stiffening members without strengthening individual components. The study also shows that traditional assessment procedures have limited capability to evaluate earthquake resistance in existing buildings with low ductility. The developed procedure provides an essential tool for comparative assessments of retrofitting scenarios and profitability evaluations. Full article

This study investigates the seismic response of two 20-story adjacent reinforced concrete structures with differing lateral load-bearing systems, emphasizing the influence of soil–structure interaction. In total, 72 numerical models explored the combined effects of 9 earthquake motions, 4 soil types, and 2 structural designs. Analytical fragility curves revealed superior seismic resilience for the structure with shear walls compared to the bare frame structure. Shear walls increased the capacity to withstand earthquakes by up to 56% for each damage level. Soil behavior analysis investigated the effect of soil properties. Softer soil exhibited larger deformations and settlements compared to stiffer soil, highlighting soil ductility’s role in the system’s response. The study further assessed potential pounding between structures. The connection between structural stiffness and soil deformability significantly affected pounding risk. The provided gap (350 mm) proved insufficient to prevent pounding under various earthquake scenarios and soil types, leading to damage to RC components. These findings emphasize the crucial need to consider both structural systems and soil properties in seismic assessments. Full article