Verification of a Stiffness-Variable Control System with Feed-Forward Predictive Earthquake Energy Analysis

Semi-active isolation systems with controllable stiffness have been widely developed in the field of seismic mitigation. Most systems with controllable stiffness perform more robustly and effectively for far-field earthquakes than for near-fault earthquakes. Consequently, a comprehensive system that provides comparable reductions in seismic responses to both near-fault and far-field excitations is required. In this regard, a new algorithm called Feed-Forward Predictive Earthquake Energy Analysis (FPEEA) is proposed to identify the ground motion characteristics of and reduce the structural responses to earthquakes. The energy distribution of the seismic velocity spectrum is considered, and the balance between the kinetic energy and potential energy is optimized to reduce the seismic energy. To demonstrate the performance of the FPEEA algorithm, a two-degree-of-freedom structure was used as the benchmark in the numerical simulation. The peak structural responses under two near-fault and far-field earthquakes of different earthquake intensities were simulated. The isolation layer displacement was suppressed most by the FPEEA, which outperformed the other three control methods. Moreover, superior control on superstructure acceleration was also supported by the FPEEA. Experimental verification was then conducted with shaking table test, and the satisfactory performance of the FPEEA on both isolation layer displacement and superstructure acceleration was demonstrated again. In summary, the proposed FPEEA has potential for practical application to unexpected near-fault and far-field earthquakes.

Evaluation of the period and soft story conditions of reinforced concrete buildings with and without infill walls

Since the ground floor of most of the buildings in our country is designed as a shop or ground floor (in the buildings created as a workplace), there is very little infill wall ratio on the ground floors due to architectural and functional reasons, and some of them do not even exist at all. However, infill walls significantly increase the horizontal rigidity and strength of the structure, thus causing a decrease in the period value that determines the earthquake loads that will affect the structure. However, the infill wall meets the first destructive forces of the earthquake, and during this time, it cracks and absorbs some of the earthquake energy. The structural system elements of the building (columns and shear walls) start to meet the earthquake forces only when the infill walls are damaged and fail. In this direction, the aim of this study is to investigate to what extent the amount of infill wall on the ground floor affects the period of the building, and whether there are soft storey irregularities in the building according to the change in the amount of infill wall on the ground floor. In this study, while there are infill walls on all floors and all axes of buildings of various heights (3, 6, 9 and 11 floors), the amount of infill walls in the x and y directions on the ground floors is reduced to a certain extent, and many models are created until the ground floor is completely without infill walls. All these models created were analyzed with the support of the SAP2000 program, and the period values were determined and examined according to the soft storey problems and compared with the case of the entire building with and without infill walls. In addition, it was examined whether the period formulas determined as a result of the studies and taking into account the infill wall give realistic results for the situation examined in this study.

Characteristics of Seismicity in the Eagle Ford Shale Play, Southern Texas, Constrained by Earthquake Relocation and Centroid Moment Tensor Inversion

Analysis of earthquake locations and centroid moment tensors (CMTs) is critical in assessing seismogenic structures and connecting earthquakes to anthropogenic activities. The objective of this study was to gain insights into the seismotectonics of the Eagle Ford Shale play (EF), southern Texas, through relative relocation of earthquakes, assessment of CMT solutions, and investigation of the background stress field. Using Texas Seismological Network (TexNet) data from 2017 through 2019, we were able to relocate 326 earthquakes and obtain CMT solutions for 37 ML≥2.0 earthquakes. These earthquakes are located in the sedimentary basin and uppermost crust, with depths ranging from 2 to 10 km. The earthquake groups in the northeastern EF are linearly distributed along the Karnes fault zone, whereas the southern and western groups are spatially scattered around mapped or unmapped faults. CMT solutions identified 32 normal fault earthquakes and five strike-slip earthquakes. The orientation of the fault plane of most normal fault earthquakes is southwest–northeast, whereas the possible fault plane of the strike-slip fault is from north-northwest to south-southeast, which is roughly perpendicular to the normal faults. Normal and strike-slip faults in the EF are of high dip angles, with the dip angles of the most faults ranging from 60° to 80°. Stress inversion results show that the major orientation of maximum horizontal stress (SHmax) is southwest–northeast, with minor local stress-field rotations. We further estimated earthquake energy release in the EF region using moment magnitude from the CMT solutions, and the cumulative earthquake energy release curve reveals three notable increases in cumulative seismic moment, which occurred in January–July 2018 and January–March 2019, and May–August 2019. Whether these energy releases were caused by anthropogenic activities is a matter for further investigation.

NORTH-EAST OF RUSSIA

The results of seismic monitoring of Magadan region, Chukotka Autonomous Area and adjacent sea shelf (Okhotsk, Chukchi, Bering and East Siberian seas) are given. The information about 12 digital seismic stations and monitoring equipment types and parameters is given. Maps of earthquake energy representativeness, seismic stations and epiсenters are presented. The distribution of earthquake number by energy classes and total seismic energy by six regions of North-East of Russia is given. The information about 234 events with energy classes КР=6.0–12.8 is included in the catalog. All hypocenters are located within the Earth's crust. Earthquake epicenters in Kolyma area are plotted on the tectonic zoning scheme. The strongest earthquake in 2014 with MPSP=4.5 (КР=12.8) occurred on July 4 in Kolyma area and was called Elgenskoe II. It was sensible with intensity I=4. Monitoring in 2014 showed decrease of seismic activity in Okhotsk sea area and its increase in the Kolyma. Spatially, all the earthquakes of the North-East of Russia are traditionally concentrated within the large seismogenic zones: the Chersky, the North Okhotsk and the Trans-Bering Sea.

A Study on the Significance of the Design Parameters of Steel Plate Shear Walls Subjected to Monotonic Loading

Steel plate shear walls (SPSWs) as a resistant system against lateral loads have a high potential for earthquake energy dissipation. Due to the uncertainties of loading, construction, and installation of SPSWs, it is vital to investigate the importance of each component and achieve higher accuracy in design and the implementation of these members. In this paper, a sensitivity analysis is carried out to determine the significance of important uncertainties. The results denoted that the most important parameters affecting the loading capacity of the SPSWs are height, thickness, length, Young’s modulus of the wall material, flange, and web thickness of the column, respectively.

Detecting Earthquake-Related Anomalies of a Borehole Strain Network Based on Multi-Channel Singular Spectrum Analysis

To investigate the nonlinear spatio-temporal behavior of earthquakes, a complex network has been built using borehole strain data from the southwestern endpoint of the Longmenshan fault zone, Sichuan-Yunnan region of China, and the topological structural properties of the network have been investigated based on data from 2011–2014. Herein, six observation sites were defined as nodes and their edges as the connections between them. We introduced Multi-channel Singular Spectrum Analysis (MSSA) to analyze periodic oscillations, earthquake-related strain, and noise in multi-site observations, and then defined the edges of the network by calculating the correlations between sites. The results of the daily degree centrality of the borehole strain network indicated that the strain network anomalies were correlatable with local seismicity associate with the earthquake energy in the strain network. Further investigation showed that strain network anomalies were more likely to appear before major earthquakes rather than after them, particularly within 30 days before an event. Anomaly acceleration rates were also found to be related to earthquake energy. This study has revealed the self-organizing pre-earthquake phenomena and verified the construction of borehole networks is a powerful tool for providing information on earthquake precursors and the dynamics of complex fault systems.

Evaluation of global seismicity along Northern and Southern hemispheres

An earthquake has been identified as one of the major natural disasters that cause loss of lives and property. To mitigate this disaster, knowledge of global seismicity is essential. This research is aimed at evaluating the Gutenberg Richter b-value parameter and focal depth distribution of earthquake parameters to identify the prominent earthquake-prone zones in the Northern and Southern hemispheres. The study area covers 20° to the Northern and Southern hemispheres, with the equator in the middle. The data were obtained from the earthquake catalogue of the Advanced National Seismic System (ANSS) hosted by the Northern California Earthquake Data Centre USA from 1963–2018. Fifty-four-year earthquake data of M ≥ 6.0 were processed and analyzed using Gutenberg-Richter (GR). The b-value parameters obtained from the GR model were plotted against the hemispheres using bar chart graphs to determine the tectonic stress level of the study region. The earthquake energy released was evaluated along the Northern and Southern hemispheres for a proper understanding of seismic events in the study region. It was observed that the rate of earthquake occurrence at the Southern hemisphere is higher than the Northern hemisphere. The b-values obtained in all the zones vary from 0.82–1.16. At the same time, the maximum earthquake energy of 4.6 × 1025 J was estimated. Low b-values indicate high tectonic stress within the plates. The large tectonic stress accumulation around the equator suggests that unstable lithospheres characterize this zone.