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Tectonic extrusion bypassing the eastern Himalayan syntaxis results in a significant increase in regional stress instability and the associated frequent occurrence of earthquakes in southern Yunnan, China. However, the stress field, and the relationship between the focal mechanism of earthquakes and stress evolution in southern Yunnan, remain enigmatic. In this paper, using a modified grid point test method, we calculated the focal mechanism of ML ≥ 2.5 earthquakes in southern Yunnan (22-25° N, 100-104° E) from January 2009 to June 2023. Utilizing the solutions of historical earthquake focal mechanisms, we obtained the present-day regional tectonic stress field in southern Yunnan via inversion. The results indicate complex and diverse seismic focal mechanisms, and the main types of earthquakes are strike-slip events, followed by normal fault and reverse fault events. The orientations of the maximum and minimum principal stress axes rotate in a clockwise direction from northeast to southwest. The internal stress orientation distribution of the rhombic Sichuan-Yunnan block in the study area is consistent, and the block boundary zone is the site where stress deflection occurs, and the regional tectonic stress field is influenced by the interaction among different blocks. The distribution of R-value in the Lamping-Simao block gradually increases from north to south, indicating that the compressive stress required for material transport becomes relatively small. Combined with the geological and tectonic background of the study area, our results suggest that the speed of block movement gradually decreases from north to south; the distribution of R-value in the South China block is significantly smaller than that of the interior of the Sichuan-Yunnan rhombus, and the proportion of compressive stresses is larger, indicating a stronger extrusion in this region, which may be related to the fact that the Sichuan-Yunnan rhombus is strongly resisted by the South China block in the east.
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The 1693 tsunami was the most extensive earthquake-tsunami event in Sicily, submerging Catania, Augusta, and Syracuse. However, the earthquake rupture, water level, arrival time, and furthest inundation distance of the tsunami waves are not yet known. This study aims to investigate the tsunamigenic source, run-up height, furthest inundation distance, and arrival time of the 1693 tsunami waves on the east coast of Sicily. Moreover, the assessment of tsunami-prone zones was also conducted based on worst-case earthquake-tsunami scenarios. Numerical modeling was applied by proposing six offshore focal mechanism scenarios using the shallow water equation in Delft3D and Delft Dashboard. The input parameters include length, width, strike, dip, slip, rake, and depth of the earthquake rupture. Meanwhile, the tsunami wave propagation onshore utilized XBeach and ArcGIS, considering the maximum run-up height, surface roughness analyzed from land use maps, slope, river existence, and coastline from Digital Terrain Model (DTM) identification. The results indicate that the worst possible impact of the 1693 tsunami was generated by an earthquake with a magnitude of Mw 7.13. The maximum water level, furthest inundation distance, and arrival time achieved 7.7 m, 318 m, and 9 min after wave generation offshore, respectively. This simulation is consistent with the discovery of 1693 tsunami deposits at a distance of less than 400 m from the coastlines of Augusta and Syracuse, but it is above the estimated furthest inundation distance in previous studies, which only reached around 100 m-200 m from the eastern coastline of Sicily. The results of the study are reliable as they align with the 1697 historical document where seawater inundated San Filippo Square, Catania.
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Mining-induced earthquakes (MIEs) in underground coal mines have been a common phenomenon that easily triggers rock bursts, but the mechanism is not understood clearly. This research investigates the laws of focal mechanism and source parameters based on focal mechanism and source parameters analysis of MIEs in three frequent rock burst areas. The relative moment tensor inversion (MTI) method was introduced, and the way to construct the inversion matrix was modified. The minimum ray and source number conditions were calculated, and an optimized identification criterion for source rupture type was proposed. Results show that the geological structure, stress environment, and source horizon influence the focal mechanism. The tensile type sources can distribute in the roof and coal seam, while the shear types are primarily located in the coal seam. In the typical fold structure area, the difference in source rupture strength and stress adjustment between tensile and shear types is negligible, while the disturbance scale of tensile types is distinct. The shear types have higher apparent volume and seismic moment in the deep buried fault area but lower source energy. The apparent stress of the tensile types is higher than that of the shear types, representing that the stress concentration still exists in the roof after the MIEs, but the stress near the faults could be effectively released. In the high-stress roadway pillar area, the primary fracture of the coal pillar easily produces a continuous shear rupture along the dominant stress direction under the extrusion of the roof and floor. The source parameters (except apparent stress) of shear types are higher than tensile types and have higher dynamic risk. The results contribute to expanding the understanding of rock burst mechanisms and guide MIEs' prevention.
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This article presents updated and unified Poissonian earthquake and focal mechanism catalogs for the United Arab Emirates and its surroundings. Data were compiled from different local, regional, and international sources. Several magnitude-conversion relationships have been applied to obtain the unified moment magnitude estimates for the final datasets. Dependent earthquakes were identified and removed from the compiled data via a declustering process to ensure a time independent Poissonian distribution of seismicity. The final compiled earthquake catalog is comprised of 1464 mainshocks, which span the time period of 658-2019 [1]. The range of their spatial region is 21°-31°N on the latitude and 47° to 66°E on the longitude. Additionally, an overall number of 583 focal mechanism solutions spanning the time period of 1923-2015 were acquired [1]. Such datasets are compatible with other published catalogs from across the globe which provide a basis for the estimation of seismic hazard and risk, as well as, the establishment of a unified seismic action representation in the building codes for the United Arab Emirates. This paper and its dataset are a companion for a published article in the Journal of Asian Earth Sciences under the title "A State-Of-The-Art Seismic Source Model for the United Arab Emirates" [2].
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Reservoir-induced earthquakes related with the construction of the Three Gorges Project have attracted great concerns of the public. Since the first water impoundment on May 25, 2003, a number of earthquakes have occurred during the water storage stages, in which the largest was the Badong M5.1 earthquake on December 16, 2013. In this paper, the relationships between seismic activities, b value, seismic parameters, and reservoir water level fluctuations are studied. In addition, based on the digital seismic waveform data obtained since 2000, the focal depth changes and focal mechanism characteristics before and after the water impoundment are studied as well. These provide us important information to understand the earthquake mechanisms. The results show that these earthquakes are typical reservoir-induced earthquakes, which are closely related to water infiltration, pore pressure, and water level fluctuations. The majority of the micro and small earthquakes are caused by karst collapse, mine collapse, bank reformation, superficial unloading, and so on. The larger earthquakes are related to the fault structures to some extent. Due to the persistent effects of water impoundment on the seismic and geological environments around the reservoir and water infiltration into the rocks, the influences on the crustal deformation field, gravity field, seepage field, and fault medium-softening action may vary gradually from a higher strength to a weaker one. Therefore, it is possible that small earthquakes and few medium earthquakes (M≤5.5) will occur in the reservoir area in the future.
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BACKGROUND: Cocaine use is a known but rare cause of cardiac arrhythmias. Ventricular arrhythmias related to cocaine may not respond to antiarrhythmic drugs and may need treatment with radiofrequency ablation. OBJECTIVES: We describe the clinical and electrophysiological characteristics of cocaine-related ventricular tachycardia (VT) from a multicenter registry. METHODS: Subjects presenting with VT related to cocaine use and being considered for radiofrequency ablation have been included in the study. Patients who were refractory to maximal medical therapy underwent radiofrequency ablation of the VT. Clinical, procedural variables, efficacy, and safety outcomes were assessed. RESULTS: A total of 14 subjects met study criteria (age 44 ± 13, range 18- to 68-year-old with 79% male, 71% Caucasian). MRI showed evidence of scar only in 43% of patients (6/14). The mechanism of VT was focal in 50% (n = 7) and scar related reentry in 50% (n = 7) based on 3D mapping. The mean VT cycle length was 429 ± 96 milliseconds. The site of origin was epicardial in 16% (3/18) of VTs. Most clinical VTs were hemodynamically stable (75%). Mean ejection fraction at the time of admission was 44 ± 14%. Duration of procedure was 289 ± 50 minutes. One subject developed pericardial tamponade requiring drainage. At 18 ± 11 months follow-up, freedom from arrhythmia was seen in 86% (1 case lost to follow-up and 2 died). CONCLUSION: Radiofrequency ablation is not only feasible but also safe and effective in patients who have drug refractory VT related to chronic cocaine use.
Asunto(s)
Ablación por Catéter , Trastornos Relacionados con Cocaína/complicaciones , Taquicardia Ventricular/cirugía , Adolescente , Adulto , Anciano , Antiarrítmicos/uso terapéutico , Ablación por Catéter/efectos adversos , Resistencia a Medicamentos , Técnicas Electrofisiológicas Cardíacas , Estudios de Factibilidad , Femenino , Hemodinámica , Humanos , Masculino , Persona de Mediana Edad , Recurrencia , Sistema de Registros , Estudios Retrospectivos , Factores de Riesgo , Volumen Sistólico , Taquicardia Ventricular/diagnóstico , Taquicardia Ventricular/etiología , Taquicardia Ventricular/fisiopatología , Factores de Tiempo , Resultado del Tratamiento , Estados Unidos , Adulto JovenRESUMEN
In kinematics, a framework is called overconstrained if its continuous flexibility is caused by particular dimensions; in the generic case, a framework of this type is rigid. Famous examples of overconstrained structures are the Bricard octahedra, the Bennett isogram, the Grünbaum framework, Bottema's 16-bar mechanism, Chasles' body-bar framework, Burmester's focal mechanism or flexible quad meshes. The aim of this paper is to present some examples in detail and to focus on their symmetry properties. It turns out that only for a few is a global symmetry a necessary condition for flexibility. Sometimes, there is a hidden symmetry, and in some cases, for example, at the flexible type-3 octahedra or at discrete Voss surfaces, there is only a local symmetry. However, there remain overconstrained frameworks where the underlying algebraic conditions for flexibility have no relation to symmetry at all.