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Earthquake source parameters estimated from high rate multi GNSS data: a case study of the 2022 M6.9 Menyuan earthquake

Li Xuechuan, Chen Changyun, Liang Hongbao, Li Yu, Zhan Wei

Acta Geophysica

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2023

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Vol. 71, no. 2

625--636

EN

The epicenter, origin time, and magnitude of the earthquake are critical earthquake source parameters, as they can provide data support for earthquake emergency rescue and earthquake risk research, among others. Here, the high-rate displacement time series of 11 Global Navigation Satellite System (GNSS) stations during the 2022 Menyuan M6.9 earthquake were acquired using GPS, GPS/GLONASS, and GPS/GLONASS/Galileo observations using the PRIDE PPP-AR software. Our analysis revealed that the root mean squares (RMS) of displacement derived from GPS/GLONASS/Galileo relative to GPS derived in the north, east, and up components were improved by 23.3, 34.4, and 24.4%, respectively. The epicenter location of the Menyuan earthquake based on GPS/GLONASS/Galileo-derived time series of each station was 101.201°E and 37.791°N, the earthquake origin time was 17:45:23.7 (UTC), and the moment magnitude was 6.62, which were more accurate than the GPS and GPS/GLONASS results. Although there was no significant advantage of calculating the coseismic displacement by multi-day static solution from GPS/GLONASS/Galileo, our results showed that the multi-GNSS combination can improve the stability of time series and reduce noise, and more realistically describe the surface displacement changes during earthquakes; accuracy of earthquake source parameters estimation, can, therefore, be improved with the use of multi-GNSS data.

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Crustal deformation characteristics in the southwest segment of the Longmenshan structural belt before Lushan Mw6.6 earthquake and seismogenic structural model

Xu Dongzhuo, Li Shenghu, Ta La, Luo Sanming, Zhan Wei, Zhu Wenwu, Shen Xing

Acta Geophysica

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2021

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Vol. 69, no. 5

1597--1608

EN

Based on the calculation of precise leveling and GPS observation data, the crustal deformation characteristics of the southwest segment of Longmenshan structural belt before the Lushan Mw6.6 earthquake were analyzed. The results indicate: (1) Before the Lushan earthquake, the focus area and the SW section of the Longmenshan structure zone underwent weak crustal deformation and had large-scale crustal stress strengthening. The crustal deformation feld was in a locking state, and the far-feld area to the NW underwent obvious crustal deformation. This large-scale crustal deformation weakening or even locking phenomenon has a certain indicative signifcance for the occurrence of future moderately strong earthquakes in the same tectonic background area. (2) The Wenchuan earthquake caused the adjustment of the tectonic stress from the plateau and accelerated the accumulation of stress in the SW part of the Longmenshan structural belt, which contributed to the Lushan earthquake to a certain degree. (3) The seismogenic structure of the Lushan earthquake is not a simple thrusttype structure, but more likely to be an immature and complex blind thrust fault pattern that developed during the expansion and growth period of the multiple thrust nappe structural system. The seismogenic mechanism has reference value for the prediction of moderately strong earthquakes and scientifc research in the periphery of the continental plateau.

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Combination of the Levenberg–Marquardt and diferential evolution algorithms for the ftting of postseismic GPS time series

Li Jingwei, Zhan Wei, Guo Bofeng, Li Shuiping, Guo Binghui

Acta Geophysica

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2021

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Vol. 69, no. 2

405--414

EN

Postseismic global positioning system (GPS) time series are of fundamental importance for investigating the physical mechanisms of postseismic deformations, as well as the construction and maintenance of terrestrial reference frames. Particularly, methods for constructing accurate ftting models for such time series are critical. Based on the physical features of postseismic deformation models, we propose a new algorithm that combines the strengths of the Levenberg–Marquardt (LM) and dif ferential evolution (DE) algorithms, that is, the LM+DE algorithm. In this algorithm, the parameters are initialised by the constrained DE algorithm; the fnal parameters of the postseismic model are then solved by the LM algorithm. To validate the proposed method, DE, LM, and LM+DE were compared using synthetic and observational data from the 2011 Tohoku Earthquake. For all tests based on synthetic data, the LM+DE algorithm consistently converged to the global solution and the residual is small, regardless of how the independent parameter was varied. In the 2011 Tohoku earthquake, the parameters calculated by the LM+DE algorithm matched consistently for the global solution with a 100% passing rate after constraints were provided for the ratios of the initial relaxation time parameters. In contrast, the LM and DE algorithms individually achieved passing rates of only 22% and 1%, respectively. These results demonstrate that the proposed LM+DE algorithm efectively solves the initial estimate problem in the ftting of nonlinear postseismic models, and also ensures that the fts are mathematically optimal and consistent with physical reality.