Earthquake Research Advances最新文献

Geodetic observations have shown that there exist large differences in the viscosity of the deep lithosphere across many large strike-slip faults. Heterogeneity in lithospheric viscosity structure can influence the efficiency of stress transfer and thus may have a significant effect on the earthquake cycle. Until now, how the lateral viscosity variation across strike-slip faults affects the earthquake cycles is still not well understood. Here, we investigate the effects of across-strike viscosity variation on long-term earthquake behaviors with a three-dimensional strike-slip fault model. Our model is a quasi-static model which is controlled by the slip-weakening friction law and power-law rheology. By comparing with the reference case, we find that low viscosity on one side of the fault results in a smaller rupture area but with a higher Coulomb stress drop on the ruptured fault region. In addition, low viscosity also leads to a small Coulomb stress accumulation rate. These combined effects increase the earthquake recurrence interval by approximately 10% and the earthquake moments by about 30% when the low viscosity is related to a geothermal gradient of 30 ​K/km. In addition, across-strike viscosity variation causes asymmetric interseismic ground surface deformation rate. As the viscosity contrast increases, the difference in the interseismic ground surface deformation rate between the two sides of the fault gradually increases, although the asymmetric feature is not pronounced. This asymmetry of interseismic ground deformation rate across a strike-slip fault is supposed to result in asymmetric coseismic deformation if the long-term plate motion velocity is invariant. As a result, this kind of asymmetry of interseismic deformation may influence the evaluation of potential earthquake hazards along large strike-slip faults with lateral viscosity contrast.

Traditional visual interpretation is often inefficient due to its excessively workload professional knowledge and strong subjectivity. Therefore, building an automatic interpretation model on high spatial resolution remote sensing images is the key to the quick and efficient interpretation of earthquake-triggered landslides. Aiming at addressing this problem, a landslide interpretation model of high-resolution images based on bag of visual word (BoVW) feature was proposed. The high-resolution images were pre-processed, and then BoVW feature and support vector machine (SVM) was adopted to establish an automatic landslide interpretation model. This model was further compared with the currently widely used Histogram of Oriented Gradient(HoG) feature extraction model. In order to test the effectiveness of the method, typical landslide images were selected to construct a landslide sample library, which was subsequently utilized as the foundation for conducting an experimental study. The results show that the accuracy of landslide extraction using this method reaches as high as 89%, indicating that the method can be used for the automatic interpretation of landslides in disaster-prone areas, and has high practical value for regional disaster prevention and damage reduction.

On September 5, 2022, at Beijing time 12:52 p.m., an M_S 6.8 earthquake struck Luding County, Garze Tibetan Autonomous Prefecture, Sichuan Province. The epicenter of the earthquake was at the intersection of the Sichuan-Yunnan, Bayankala, and South China blocks. The tectonic background is extremely complex, and strong earthquakes occur frequently. Based on a predetermined focal location and focal mechanism solution for the earthquake, we reversed the focal depth and rupture process of the earthquake by fitting the teleseismic P and SH waves recorded by the global seismic network. The results show that the focal depth is 16 ​km, with the main rupture having a length of about 45 ​km near the epicenter, with a maximum displacement of 1.02 ​m. Although the rupture mainly propagates from the north–northwest (NNW) to the south–southeast (SSE) along the fault strike, there is a small-scale rupture slip zone at shallow depths in the north–northeast (NNE) direction along the epicenter of the seismogenic fault. This rupture image corresponds to the cluster distribution of aftershocks in the NNW and SSE directions starting from the epicenter, corresponding to the distribution of recorded landslides. The earthquake occurred on the Moxi fault, located in the southeastern section of the Xianshuihe fault. The major tectonic feature in this area is the southeastward movement of the Chuandian block relative to the Bayanhar block.

Piezoelectric material, as one of the great potential materials, had attracted lots of attention all over the world due to its distinguish advantages. In this paper, the development of piezoelectric-based technology for application in the field of civil structural health monitoring (CSHM), was summarized and discussed. Based on the different identification mechanisms, the piezoelectric transducer-based technology can be divided into two main approaches as the active or passive sensing and detection methods. This paper summarized the development of these two approaches and discussed their applications in the area of civil structural health monitoring, such as structural and concrete engineering, bridge engineering, pipeline engineering, protection engineering for geological hazards and earthquake disasters, and so on. In addition, the electrical mechanical impedance (EMI) technique, as one of the active identification methods, was also detailly presented. Finally, its great potential for the piezoelectric-based technique was presented based on the detail discussion, especially in the areas of civil structural health monitoring.

We measure spatio-temporal variations of seismic velocity changes in Salton Sea Geothermal Field, California based on cross correlations of daily seismic traces recorded by a borehole seismic network from December 2007 to January 2014. We find clear co-seismic velocity reductions during the 2010 M 7.2 ​El Mayor–Cucapah, Mexico earthquake at ∼100 ​km further south, followed by long-term recoveries. The co-seismic reductions are larger with longer post-seismic recoveries in higher frequency bands, indicating that material damage and healing process mostly occurred in the shallow depth. In addition, the co-seismic velocity reductions are larger for ray paths outside the active fluid injection/extraction regions. The ray paths inside injection/extraction regions are associated with smaller co-seismic reductions, but subtle long-term velocity increases. We also build 3D transient water flow models based on monthly injection/extraction rates, and find correlations between several water flow parameters and co-seismic velocity reductions. We interpret the relative lack of co-seismic velocity changes within the geothermal region as unclogging of fracture network due to persistent fluid flows of geothermal production. The long-term velocity increase is likely associated with the ground water depletion and subsidence due to net production.

Temporary seismic network deployments often suffer from incorrect timing records and thus pose a challenge to fully utilize the valuable data. To inspect and fix such time problems, the ambient noise cross-correlation function (NCCF) has been widely adopted by using daily waveforms. However, it is still challenging to detect the short-term clock drift and overcome the influence of local noise on NCCF. To address these challenges, we conduct a study on two temporary datasets, including an ocean-bottom-seismometer (OBS) dataset from the southern Mariana subduction zone and a dataset from a temporary dense network from the Weiyuan shale gas field, Sichuan, China. We first inspect the teleseismic and local event waveforms to evaluate the overall clock drift and data quality for both datasets. For the OBS dataset, NCCF using different time segments (3, 6, and 12-h) beside daily waveforms data is computed to select the data length with optimal detection capability. Eventually, the 6-h segment is the preferred choice with high detection efficiency and low noise level. For the land dataset, higher drift detection is achieved by NCCF using the daily long waveforms. Meanwhile, we find that NCCF symmetry on the dense array is highly influenced by localized intense noise for large interstation distances (>1 ​km) but is well preserved for short interstation distances. The results have shown that the use of different segments of daily waveform data in the OBS dataset, and the careful selection of interstation distances in the land dataset substantially improved the NCCF results. All the clock drifts in both datasets are successfully corrected and verified with waveforms and NCCF. The newly developed strategies using short-segment NCCF help to overcome the existing issues to correct the clock drift of seismic data.

In a conventional base isolation system, minimizing the seismic responses of the superstructure is always at the cost of increasing the isolator's response. The semi-active control of the isolator has been considered an effective solution to such a dilemma. It tunes the real-time properties of the isolator according to preset rules to further reduce the superstructure's seismic responses without increasing that of the isolator or vice versa. However, the number of ground motion records used to design and validate the controller, i.e., the preset rules, in existing studies is usually very small and therefore is suspectable if it is adequate to address the significant uncertainty in the shaking of future earthquakes. This paper critically reviews the performance of the proportional-integral-derivative (PID), linear-quadratic regulator (LQR), and fuzzy controllers in semi-active base isolation systems with magnetorheological (MR) dampers subjected to highly uncertain ground motion inputs through numerical simulations. The results show that the control performance of the controllers varies significantly with the increasing number of input records, suggesting the necessity of using at least 50 ground motion records to appropriately assess the performance uncertainty of semi-active base isolation systems. More importantly, the superior performance of the optimized controllers is not guaranteed if the system is subjected to ground motions that are new to the controller, even if the controller has been optimized for thousands of existing ground motions. It highlights the need of improving the adaptability of the semi-active systems for uncertain ground motion inputs.

The traces left by earthquakes in lacustrine sediments are studied to determine the occurrence of ancient earthquakes by identifying seismically induced soft-sediment deformation structures (SSDS). Dating can help reconstruct the relative frequency of earthquakes. Identifying seismically induced seismites, which carry abundant seismic information from numerous SSDS, is both critical and challenging. Studying the deformation mechanism of SSDS and learning about the common criteria of seismically induced SSDS improve the identification of earthquake triggers. With better research into SSDS, seismic events can be effectively captured, and temporal constraints can be carried out by ¹⁴C dating and optically stimulated luminescence (OSL) dating to identify and date the occurrence of ancient earthquakes. The present contribution primarily addresses the meaning and mechanism of SSDS and their relationship with earthquake magnitude as well as the common criteria of the SSDS induced by earthquakes.

At 12:52, September 5, 2022, an M_S 6.8 earthquake occurred in Luding, Sichuan. The earthquake caused serious casualties and property loss, and was determined to have an epicenter intensity of IX degree. In this study, we used three earthquake intensity rapid assessment methods (i.e. WFM, BPM and ASM) to evaluate the intensity of this earthquake. Then, we comparatively analyzed the three methods based on strong ground motion observation data and actual intensity maps. The results show that: (1) The earthquake is associated with a southeast-oriented single-sided rupture. The WFM method can only evaluate earthquakes with two-sided ruptures, which has some limitations; (2) The intensity of BPM and ASM was overestimated on the southwest and north sides of the epicenter, but other high-intensity zones were similar to the intensities measured by actual surveys; (3) The residuals of the three intensity assessment methods were all between −0.5 and 1. Although a small number of stations were underestimated, the overall residuals were good, and the residuals gradually approached 0 with the increase of distance; (4) The number of towns and villages evaluated by the three methods in the earthquake area was almost all lower than the field survey results. One exception is the area of VIII degree, where the BPM and ASM were higher than the survey results; (5) The area of the earthquake area evaluated by the three methods was low in VI and VII degree, moderate in VIII degree, and low in IX degree (the area from ASM is similar to the area measured by actual survey). Overall, ASM is applicable to this earthquake intensity assessment.

The report summarizes the observed damage to a variety of buildings near the epicenter of the M6.8 Luding earthquake in Sichuan Province, China. They include base-isolated buildings, multi-story reinforced concrete (RC) frame buildings, and masonry buildings. The near-field region is known to be tectonically highly active, and the local intensity level is the highest, that is, 0.4g peak ground acceleration (PGA) for the design basis earthquake, in the Chinese zonation of seismic ground motion parameters. The extent of damage ranged from the weak-story collapse that claimed lives to the extensive nonstructural damage that suspended occupancy. The report highlights the first observation of the destruction of rubber bearings and viscous dampers in the isolation layer of Chinese seismically isolated buildings. It also features the rare observation of the brittle shear failure of RC columns in moment-resisting frames in a region of such a high seismic design requirement. Possible reasons that may have attributed to the reported damage are suggested by providing facts observed in the field. However, careful forensic analyses are needed before any conclusive judgment can be made.