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Comparative study on grounding resistance measurement method of geo-electric resistivity electrode in geo-resistivity observation
Zhang Yu, Wang Lanwei, Hu Zhe
, Available online  , doi: 10.11939/jass.20210151
When using the traditional three electrode method to measure the underground electrode grounding resistance, there will be a large measurement error, which suggests that the method will not be suitable for the underground electrode ground resistance measurement. In view of this problem, this paper proposes a new method for measuring the electrode grounding resistance by using the geo-electric resistivity observation system, which is so called direct measurement method. Furthermore, the grounding resistances of the underground observation power supply electrodes of Pinggu seismic station of Beijing were measured by using the traditional three-pole method and the direct measurement method. The measurement results show that, compared with the traditional three pole method, the direct measurement method can get more reliable measurement results with less error, and saves man power and measuring time.
Shallow velocity structure and seismogenic environment in the Zigui section of the Three Gorges Reservoir region of China
Hu Jintao, Xie Jun, Wei Zigen, Jin Chao
, Available online  , doi: 10.11939/jass.20210194
After the impoundment of the Three Gorges Reservoir in 2003, shallow earthquakes occurred frequently, which had a great impact on local productions and lives. The study of shallow velocity structure is of great significance for shallow seismic disaster assessment and disaster prevention and reduction in Zigui area. In this paper, based on the vertical component continuous waveform records of 24 mobile seismic stations in Zigui area from June to July of 2020, the empirical Green’s functions between stations are obtained by cross-correlating of the ambient seismic noise, the Rayleigh wave group velocity dispersion curves of 0.6−5 s are extracted, and the inversion for the three-dimensional S-wave velocity model is obtained within 6 km near the surface of the region. The results show that the S-wave velocity of Zigui basin and its south adjacent area is significantly lower than that of the eastern fault area, which is consistent with the structural evolution and sedimentary characteristics of different structural blocks in the studied area; an earthquake with MS4.2 occurred on the vertical high-velocity and low-velocity junction area of the study area in 2014. The S-wave velocity decreases obviously near the Yangtze River region in the fault zone, indicating that the Yangtze River water penetrates into the fault area. Therefore, the frequent occurrence of earthquakes in Zigui area is related to the water load and water infiltration of the Three Gorges reservoir.
Applicability of the Next Generation Attenuation-West2 ground-motion model to the components of near-fault velocity pulse-like ground motions
Zhao Xiaofen, Wen Zengping, Xie Junju, Xie Quancai
, Available online  , doi: 10.11939/jass.20210176
The traditional ground-motion models (GMMs) do not account for pulse effects and may therefore fail to estimate seismic hazards and risk at near-fault sites, where pulse-like ground motions are expected. Thus, the applicability of the newest generation NGA-West2 GMMs to the near-fault velocity pulse-like ground motions need to be tested. The near-fault strong ground motions are quantitatively identified by considering the uncertainty of pulse orientation and using wavelet method from recent earthquake since 2013 to form a new pulse database. Based on the new pulse database, long-period pulses are extracted from the original pulse records by using wavelet method. Based on a quantitative analysis of the epsilon parameter, we quantitatively test the applicability of the NGA-West2 ground-motion model to the near-fault velocity pulse-like ground motions. The results show that the four NGA-West2 models are more suitable for describing the residual recordings at the studied period, but underestimate the pulse original ground motions especially around the pulse period. We noted that, during the four NGA-West2 models, the applicability of the CB2018 to the residual ground motions is the best. This study provides an excellent opportunity to quantitatively evaluate the NGA-West2 GMMs and to update these models in the near future, and also provides a basis for incorporating pulse effects into near-fault probabilistic seismic hazard analysis and seismic design.