Geodesy and Geodynamics最新文献

This study analyzed the vertical deformation before and after the 2022 Menyuan Ms6.9 earthquake in Qinghai Province, China, using leveling profiles across faults measured from Minle County in Gansu Province to Menyuan County in Qinghai Province. Our results suggest the following: (1) The amplitude of regional vertical differential motion near the Sunna-Qilian and Lenglongling faults within the Qilian Shan increased before the 2022 Menyuan earthquake. It was accompanied by the emergence of high gradient deformation zones. Deformation at the Tongziba cross-fault leveling site near the Sunan-Qilian fault was considerable. In contrast, deformation at the Daliang cross-fault leveling site near the stepover region (adjacent to the epicenter) between the Lenglongling and Tuolaishan faults was minor. After 2018, vertical deformation at the Tongziba site notably accelerated, while that at the Daliang site was insignificant. (2) After the 2022 Menyuan earthquake, 140–150 mm of subsidence deformation occurred near the Daliang site, while the Tongziba site did not experience significant deformation. (3) Vertical deformation before and after the 2022 Menyuan earthquake conforms with the elastic-rebound theory, and the evolution of pre-earthquake deformation was consistent with the strike-slip fault deformation pattern at different seismogenic stages, i.e., the relative motion near the locked fault in the late seismogenic stage gradually weakened. The characteristics of strain accumulation and release derived from the vertical deformation before and after the Menyuan M_S6.9 earthquake help understand the deformation process of earthquake preparation and earthquake precursors.

In this study, we estimated the weekly Gravity Recovery and Climate Experiment (GRACE) spherical harmonic (SH) solutions and regional mascon solutions using GRACE-based Geopotential Difference (GPD) data and investigated their abilities in retrieving terrestrial water storage (TWS) changes over the Amazon River Basin (ARB) from January 2003 to February 2013. The performance of the weekly GPD-SH and GPD-mascon solutions was evaluated by comparing them with the weekly GFZ-SH solutions, Global Land Data Assimilation Systems (GLDAS)-NOAH hydrological model outputs, and monthly GFZ-SH, GPD-SH, and CSR-mascon solutions in the spatio-temporal and spectral domains. The results demonstrate that the weekly GPD-SH and GPD-mascon present good consistency with the weekly GFZ-SH solutions and GLDAS-NOAH estimates in the spatio-temporal domains, but GPD-mascon presents stronger signal amplitudes and more spatial details. The comparison of the monthly average of weekly estimates and monthly solutions demonstrates that the weekly GPD-mascon and GFZ-SH with DDK1 filtering are close to the monthly CSR-mascon and GFZ-SH solutions, respectively. However, the signal amplitudes of TWS changes from GPD-SH and GFZ-SH with 650 km Gaussian filtering are smaller than the monthly solutions, and the corresponding Root Mean Square Errors between the TWS change time series from the monthly average of weekly solutions and monthly estimates are 18.12 mm (GPD-mascon), 18.81 mm (GFZ-SH-DDK1), 24.93 mm (GPD-SH-G650km), and 33.07 mm (GFZ-SH-G650km), respectively. Additionally, the TWS change time series derived from weekly solutions present more high-frequency time-varying information than monthly solutions. Furthermore, the 300 km Gaussian filtering can improve the signal amplitudes of TWS changes from the weekly GPD-SH solutions more than those with 650 km Gaussian filtering, but the corresponding noise level is higher. The weekly GPD-SH and GPD-mascon solutions can extend the application scopes of GRACE and provide good complements to the current GRACE monthly solutions.

Global navigation satellite system (GNSS) technique has irreplaceable advantages in the continuous monitoring of surface deformation. Reducing noise to improve the signal-to-noise ratio (SNR) and extract the concerned signals is of great significance. As an improved algorithm of empirical mode decomposition (EMD), complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) algorithm has better signal processing ability. Using the CEEMDAN algorithm, the height time series of 29 GNSS stations in Chinese mainland were analyzed, and good denoising effects and extraction from periodic signals were achieved. The numerical results showed that the annual signal obtained with the CEEMDAN algorithm was significantly based on Lomb_Scargle spectrum analysis, and large differences in the long-term signals were found between the stations at different locations in Chinese mainland. With respect to data denoising, compared with the EMD and wavelet denoising algorithms, the CEEMDAN algorithm respectively improved the SNR by 29.35% and 36.54%, increased the correlation coefficient by 8.67% and 11.96%, and reduced root mean square error (RMSE) by 44.68% and 43.48%, indicating that the CEEMDAN algorithm had better denoising behavior than the other two algorithms. In addition, the results demonstrated that different denoising methods had little influence on estimating the annual vertical deformation velocity. The extraction of periodic signals showed that more components were retained by using the CEEMDAN algorithm than the EMD algorithm, which indicated that the CEEMDAN algorithm had advantages over frequency aliasing. In conclusion, the CEEMDAN algorithm was recommended for processing the GNSS height time series to analyze the vertical deformation due to its excellent features of denoising and the extraction of periodic signals.

On January 8, 2022, a 6.9 magnitude earthquake occurred in Menyuan County, Qinghai Province, with the epicenter located at the intersection of the Tuolaishan Fault and the Lenglongling Fault, which are part of the Qilian–Haiyuan fault zone. This study investigated the sliding characteristics and seismic mechanism of the earthquake to understand the activity and seismic risk of the fault on the northeastern margin of the Qinghai–Tibet Plateau. This paper analyzed Sentinel-1 synthetic aperture radar images to obtain the coseismic deformation field of the earthquake, which was then used to invert the slip distribution of the seismogenic fault and the coseismic Coulomb stress on the surrounding faults caused by the earthquake. It was found that the earthquake was primarily characterized by sinistral strike-slip movement. Along the satellite line of sight, the south wall of the fault had a maximum deformation of 0.62 m, and the north wall had a maximum deformation of 0.48 m. The coseismic slip distribution results indicated that the maximum slip of the earthquake was 4.51 m, and the moment magnitude was M_W6.7. The Coulomb stress analysis showed that the 2016 Menyuan earthquake promoted the occurrence of the 2022 Menyuan earthquake.

Currently, the extraction of coseismic offset signals primarily relies on earthquake catalog data to determine the occurrence time of earthquakes. This is followed by the process of differencing the average GPS coordinate time series data, with a time interval of 3 to 5 days before and after the earthquake. In the face of the huge amount of GPS coordinate time series data today, the conventional approach of relying on earthquake catalog data to assist in obtaining coseismic offset signals has become increasingly burdensome. To address this problem, we propose a new method for automatically detecting coseismic offset signals in GPS coordinate time series without an extra earthquake catalog for reference. Firstly, we pre-process the GPS coordinate time series data for filtering out stations with significant observations missing and detecting and removing outliers. Secondly, we eliminate other signals and errors in the GPS coordinate time series, such as trend and seasonal signals, leaving the coseismic offset signals as the primary signal. The resulting coordinate time series is then modeled using the first-order difference and data stacking method. The modeling method enables automatic detection of the coseismic offset signals in the GPS coordinate time series. The aforementioned method is applied to automatically detect coseismic offset signals using simulated data and the Searles Valley GPS data in California, USA. The results demonstrate the efficacy of our proposed method, successfully detecting coseismic offsets from vast amounts of GPS coordinate time series data.

The Laji Shan–Jishi Shan tectonic belt (LJTB), located in the southern part of the northeastern Tibetan Plateau (NETP), is a tectonic window to reveal regional tectonic deformation in the NETP. However, its kinematics in the Holocene remains controversial. We obtain the latest and dense horizontal velocity field based on data collected from our newly constructed and existing GNSS stations. Combined with fault kinematics from geologic observations, we analyze the crustal deformation characteristics along the LJTB. The results show that: (1) The Laji Shan fault (LJF) is inactive, and the northwest-oriented Jishi Shan fault (JSF) exhibits a significant dextral and thrust slip. (2) The transpression along the arc-shaped LJTB accommodates deformation transformation between the dextral Riyue Shan fault and the sinistral west Qinling fault. (3) With the continuous pushing of the Indian plate, internal strains in the Tibetan Plateau are continuously transferred in the northeast via the LJTB as they are gradually dissipated near the LJTB and translated into significant crustal uplift in these regions.

The Debao M_S4.8 earthquake occurred in western Guangxi on August 5, 2021, near where the Jingxi M_S5.2 earthquake occurred in 2019. To study the increasing seismicity in western Guangxi, it is necessary to determine whether there was an anomaly related to the earthquake source near the Pingxiang gravity station, which is located approximately 100 km from the epicenter of the Debao M_S4.8 earthquake. In this study, the R-value scoring method was used to analyze the anomaly and evaluate the prediction efficiency of the double frequency (DF) micro-seismic signal vertical displacement (referred to as vertical displacement, VD) and the absolute value of monthly extreme rate (referred to as the monthly rate). Results show that earthquakes larger than M_S4.0 in the 350 km range from the Pingxiang station tend to coincide with yearly typhoons, and the VD of micro-seismic signals correspondingly changes from low to high. The Debao M_S4.8 earthquake occurred during a gradual VD increase from 0.05 × 10⁻⁶ to 0.10 × 10⁻⁶ m. When discussing the relationships among R, the rate threshold, and the effective duration of prediction, the rate threshold of the micro-seismic signal converges from 0.00039 × 10⁻⁶ to 0.00031 × 10⁻⁶ m/month, the effective duration of prediction is approximately 6–10 months, and R also converges from 0.29 to 0.31. By comparing the results of three gPhone gravity stations in Guangxi, we found that the increase of short-term VD before the Debao earthquake was related to the enhancement of the DF micro-seismic signal excited by the typhoon. When the typhoon track was perpendicular to the coastline of China, the possibility of an earthquake occurring was increased. This study provides evidence and reference for the future occurrence period of earthquakes above M_S4.0 in western Guangxi.

High-precision time-varying gravity field is an effective way to study the internal mass movement and understanding the spatio-temporal evolution process of the geodynamic system. Compared to the satellite gravity measurement, the repeated terrestrial gravity observation can provide a more high-order signal related to the shallow crust and subsurface. However, the suitable and unified method for gravity model estimation is a key problem for further applications. In this study, we introduce the spherical hexahedron element to simulate the field source mass and forward model the change of gravity field located at the Sichuan-Yunnan region (99–104°E, 23–29°N) in the four epochs from 2015 to 2017. Compared to the experimental results based on Slepian or spherical harmonics frequency domain method, this alternative approach is suitable for constructing the equivalent mass source model of regional-scale gravity data, by introducing the first-order smooth prior condition of gravity time-varying signal to suppress the high-frequency component of the signal. The results can provide a higher spatial resolution reference for regional gravity field modeling in the Sichuan-Yunnan region.