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Integrated observations on crustal strain‑ionosphere total electron content anomalies before the earthquake

Sharma Gopal, Singh Mutum Somorjit, Aggarwal Shiv Prasad, Romero-Andrade Rosendo

Acta Geophysica

2023

Vol. 71, no. 3

1173--1185

Changes in strain (Linear and triangular) rate and Ionosphere Total Electron Content (TEC) before Mw 7.9 2018 Alaska Earthquake are investigated. Ten years of global positioning system (GPS) time series solutions were used for strain estimation in the region before the occurrence of the earthquake using the Haversine formula and triangulation method. Linear strain values suggest an anomaly in strain variation trend near the epicenter. Additionally, daily TEC variations for 30 days before the earthquake occurred were monitored and analysed. Analysis suggests TEC depletion on December 26 2017, and January 16 2018, respectively. TEC values from 60 GPS stations data were interpolated to study the spatial variations of TEC anomaly. Hourly TEC data derived from GPS stations on December 26 2017, and January 16 2018, suggest low TEC zone concentration near to the earthquake epicenter during 1 to 4 UTC. Spatial distribution of TEC values in 2-Dimension corresponding to anomaly time at 60 GPS stations in the vicinity of study area suggests lowest TEC values at stations that lie closer to the epicenter. The study suggests Lithosphere-Ionosphere coupling before Mw 7.9 2018 Alaska Earthquake and recommends developing a TEC-Strain Monitoring System for further validation of the work and for the better study of earthquake precursors based on TEC-Strain anomalies.

Microstructural characterization and mechanical properties of Mg-xSn-Al-Zn alloys

Kim B., Jeon J., Park K., Park B., Park Y., Park I.

Archives of Materials Science and Engineering

2008

Vol. 30, nr 2

93-96

Purpose: In this study, the microstructure and mechanical properties of as-cast Mg-xSn-Al-Zn alloys were investigated. Design/methodology/approach: Ingot was fabricated by a squeeze cast. The alloys were induction melted at 750stopniC in a mild steel crucible under CO2+2%SF6 mixed gas atmosphere and cast into a permanent mould coated with boron nitride spray held at approximately 350 stopniC . Tensile tests were carried out at room temperature in a screw-driven tensile testing machine and crosshead speed was 0.2 mm/min. Microstructural observation was carried out using a optical microscope (OM) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDS). Findings: It is found that the tensile strength and elongation decreased at room temperature increased with Sn concentration. As a consequence, 5wt% Sn addition was the one exhibiting the best tensile properties at room temperature. The micro-hardness of the alloy continuously increased with increasing the Sn concentration. Practical implications: The investigations of microstructure of commercially magnesium alloys are important for achieving desired mechanical behaviour of the material. Originality/value: The fracture behaviors of magnesium alloys are investigated.