Geodesy and Geodynamics最新文献

A method is proposed to fuse the velocity data of the global navigation satellite system (GNSS) and leveling height via combined adjustment with constraints. First, stable GNSS–leveling points are uniformly selected, and the constraints of the geodetic height change velocity and normal height change velocity are given. Then, the GNSS vertical velocities and leveling height difference are used as observations of combined adjustment, and robust least-squares estimation are used to estimate the velocities of the unknown points. Finally, a vertical movement model is established with the GNSS vertical velocities and leveling vertical velocities obtained via combined adjustment. Data from the second-order leveling network and GNSS control points in Shandong Province are taken as test data, and eight calculation schemes are used for discussion. One of the schemes, the bifactor robust combined adjustment method based on variance component estimation with two kinds of vertical velocity constraints achieves the optimal results. The method applied in the scheme can be recommended for data fusion of GNSS and leveling, further improving the reliability of vertical crustal movement in Shandong Province.

The Earth's Free Core Nutation (FCN) causes Earth tides and forced nutation with frequencies close to the FCN that exhibit resonance effects. High-precision superconducting gravimeter (SG) and very long baseline interferometry (VLBI) provide good observation techniques for detecting the FCN parameters. However, some choices in data processing and solution procedures increase the uncertainty of the FCN parameters. In this study, we analyzed the differences and the effectiveness of weight function and ocean tide corrections in the FCN parameter detection using synthetic data, SG data from thirty-one stations, and the 10 celestial pole offset (CPO) series. The results show that significant discrepancies are caused by different computing options for a single SG station. The stacking method, which results in a variation of 0.24–5 sidereal days (SDs) in the FCN period (T) and 10³-10⁴ in the quality factor (Q) due to the selection of the weighting function and the ocean tide model (OTM), can effectively suppress this influence. The statistical analysis results of synthetic data shows that although different weight choices, while adjusting the proportion of diurnal tidal waves involved, do not significantly improve the accuracy of fitted FCN parameters from gravity observations. The study evaluated a series of OTMs using the loading correction efficiency. The fitting of FCN parameters can be improved by selecting the mean of appropriate OTMs based on the evaluation results. Through the estimation of the FCN parameters based on the forced nutation, it was found that the weight function P₁ is more suitable than others, and different CPO series (after 2009) resulted in a difference of 0.4 SDs in the T and of 10³ in the Q. We estimated the FCN parameters for SG (T = 430.4 ± 1.5 SDs and Q = 1.52 × 10⁴ ± 2.5 × 10³) and for VLBI (T = 429.8 ± 0.7 SDs, Q = 1.88 × 10⁴ ± 2.1 × 10³).

Short-term (up to 30 days) predictions of Earth Rotation Parameters (ERPs) such as Polar Motion (PM: PMX and PMY) play an essential role in real-time applications related to high-precision reference frame conversion. Currently, least squares (LS) + auto-regressive (AR) hybrid method is one of the main techniques of PM prediction. Besides, the weighted LS + AR hybrid method performs well for PM short-term prediction. However, the corresponding covariance information of LS fitting residuals deserves further exploration in the AR model. In this study, we have derived a modified stochastic model for the LS + AR hybrid method, namely the weighted LS + weighted AR hybrid method. By using the PM data products of IERS EOP 14 C04, the numerical results indicate that for PM short-term forecasting, the proposed weighted LS + weighted AR hybrid method shows an advantage over both the LS + AR hybrid method and the weighted LS + AR hybrid method. Compared to the mean absolute errors (MAEs) of PMX/PMY short-term prediction of the LS + AR hybrid method and the weighted LS + AR hybrid method, the weighted LS + weighted AR hybrid method shows average improvements of 6.61%/12.08% and 0.24%/11.65%, respectively. Besides, for the slopes of the linear regression lines fitted to the errors of each method, the growth of the prediction error of the proposed method is slower than that of the other two methods.

Three M_W > 7.0 earthquakes in 2020–2021 occurred in the Shumagin seismic gap and its adjacent area of the Alaska-Aleutian subduction zone, including the M_W7.8 Simeonof thrust earthquake on July 22, 2020, the M_W7.6 Sand Point strike-slip earthquake on October 19, 2020, and the M_W8.2 Chignik thrust earthquake on July 29, 2021. The spatial and temporal proximity of these three earthquakes prompts us to probe stress-triggering effects among them. Here we examine the coseismic Coulomb stress change imparted by the three earthquakes and their influence on the subduction interface. Our results show that: (1) The Simeonof earthquake has strong loading effects on the subsequent Sand Point and Chignik earthquakes, with the Coulomb stress changes of 3.95 bars and 2.89 bars, respectively. The Coulomb stress change caused by the Sand Point earthquake at the hypocenter of the Chignik earthquake is merely around 0.01 bars, suggesting the negligible triggering effect on the latter earthquake; (2) The triggering effects of the Simeonof, Sand Point, and Chignik earthquakes on aftershocks within three months are not well pronounced because of the triggering rates of 38%, 14%, and 43% respectively. Other factors may have played an important role in promoting the occurrence of these aftershocks, such as the roughness of the subduction interface, the complicated velocity structure of the lithosphere, and the heterogeneous prestress therein; (3) The three earthquakes caused remarkable coseismic Coulomb stress changes at the subduction interface nearby these mainshocks, with an average Coulomb stress change of 3.2 bars in the shallow region directly inwards the trench.

In this study, we estimate the absolute vertical land motions at three tidal stations with collocated Global Navigation Satellite System (GNSS) receivers over French Polynesia during the period 2007–2020, and obtain, as ancillary results, estimates of the absolute changes in sea level at the same locations. To verify our processing approach to determining vertical motion, we first modeled vertical motion at the International GNSS Service (IGS) THTI station located in the capital island of Tahiti and compared our estimate with previous independent determinations, with a good agreement. We obtained the following estimates for the vertical land motions at the tide gauges: Tubuai island, Austral Archipelago −0.92 ± 0.17 mm/yr, Vairao village, Tahiti Iti: −0.49 ± 0.39 mm/yr, Rikitea, Gambier Archipelago −0.43 ± 0.17 mm/yr. The absolute variations of the sea level are: Tubuai island, Austral Archipelago 5.25 ± 0.60 mm/yr, Vairao village, Tahiti Iti: 3.62 ± 0.52 mm/yr, Rikitea, Gambier Archipelago 1.52 ± 0.23 mm/yr. We discuss these absolute values in light of the values obtained from altimetric measurements and other means in French Polynesia.

Using 4 global reanalysis data sets, significant upward trends of precipitable water vapor (PWV) were found in the 3 time periods of 1958–2020, 1979–2020, and 2000–2020. During 1958–2020, the global PWV trends obtained using the ERA5 and JRA55 data sets are 0.19 ± 0.01 mm per decade (1.15 ± 0.31%) and 0.23 ± 0.01 mm per decade (1.45 ± 0.32%), respectively. The PWV trends obtained using the ERA5, JRA55, NCEP-NCAR, and NCEP-DOE data sets are 0.22 ± 0.01 mm per decade (1.18 ± 0.54%), 0.21 ± 0.00 mm per decade (1.76 ± 0.56%), 0.27 ± 0.01 mm per decade (2.20 ± 0.70%) and 0.28 ± 0.01 mm per decade (2.19 ± 0.70%) for the period 1979–2020. During 2000–2020, the PWV trends obtained using ERA5, JRA55, NCEP-DOE, and NCEP-NCAR data sets are 0.40 ± 0.25 mm per decade (2.66 ± 1.51%), 0.37 ± 0.24 mm per decade (2.19 ± 1.54%), 0.40 ± 0.26 mm per decade (1.96 ± 1.53%) and 0.36 ± 0.25 mm per decade (2.47 ± 1.72%), respectively. Rising PWV has a positive impact on changes in precipitation, increasing the probability of extreme precipitation and then changing the frequency of flood disasters. Therefore, exploring the relationship between PWV (derived from ERA5 and JRA55) change and flood disaster frequency from 1958 to 2020 revealed a significant positive correlation between them, with correlation coefficients of 0.68 and 0.79, respectively, which explains the effect of climate change on the increase in flood disaster frequency to a certain extent. The study can provide a reference for assessing the evolution of flood disasters and predicting their frequency trends.

The Palu M_W7.4 earthquake occurred on September 28, 2018, with the epicenter at 119.86°, 0.72°. The severe shaking caused severe damage in Central Sulawesi, especially in Palu. We conducted a postseismic deformation study to determine the deformation pattern and reduce future earthquakes' impact. Interferometric Synthetic Aperture Radar (InSAR) data were processed using LiCSBAS to get the time series. The time series data were fitted to exponential and logarithmic functions to determine the mechanism of postseismic deformation. The exponential model identified the influence of the viscoelastic mechanism, and the logarithm identified the afterslip mechanism. The Palu earthquake was fitted to logarithmic and exponential, but the logarithmic was more significant than an exponential function. Afterslip mechanism predominates, and viscoelastic mechanisms play a minor role in this postseismic deformation.

In this paper, we make a statistical analysis of the fault information of the underground fluid instruments of 12 models in China from January 2021 to May 2022 based on the Pearson correlation coefficient, and compare the fault statistics of the meteorological three-element instruments of 3 models during the study period. The results show that: (1) The numbers of faults of the underground fluid instruments of 12 models with different service times are basically positively correlated with the numbers of the corresponding instruments, with good consistency. Moreover, the automatic observation instruments (8 models) with more than 30 units are significantly correlated at a 0.05 significance level (95% confidence level). Even at a 0.01 significance level (99% confidence level), there are 7 models (7/8) with significant correlation. (2) The positive and negative correlations between the monthly average number of faults and the corresponding service times of the underground fluid instruments of 12 models with different service times are random, and there are 9 models (75%) with no significant correlation at a 0.05 significance level (95% confidence level), while 12 models (100%) with no significant correlation at a 0.01 significance level (99% confidence level). (3) The monthly average numbers of faults of the underground fluid instruments of 12 models are basically 0.02–0.05 times/(unit·month), and the overall fault frequency is low. (4) The fault statistics results of the meteorological three-element instruments of 3 models are consistent with the characteristics of the underground fluid instruments of 12 models. In general, there is no significant correlation between the fault frequency and the service time of underground fluid instruments. (5) The results of this paper demonstrate that the service time of underground fluid instruments cannot be taken as the main reason for whether to update the instruments. Similarly, the fault frequency of the instruments cannot be taken as the main reason for the service life of the instruments in the process of formulating the service life standards of underground fluid instruments.

Three A10 absolute gravimeters (AGs) were first acquired in China by the Hubei Earthquake Agency under the Belt and Road Seismic Monitoring Network Project. Although AG measuring and testing technique is not new, the purchase and simultaneous testing of 3 A10 absolute gravimeters is unprecedented in China. This study conducted the first acceptance testing of the AGs at 3 locations (the Jiufengshan Gravity Observation Station, the Global Navigation Satellite System Observation Station in Wuhan, and the Jiugongshan Observation Station in Xianning). The results were compared using a method based on expert validation, and the acceptance testing scheme was formulated by referring to the Technical Regulations for Tectonic Environment Monitoring Networks in China and Specifications for Gravimetry Control. Based on the repeatability, precision, and consistency of the measured g values, the results from each instrument were evaluated using the air pressure precision test. Comparing the instrument reference values, the final test results can identify the indicator parameters for 3 A10 AGs, the effects of the surrounding environment, and the related parameters on measurement precision. The precision of A10-059, A10-058, and A10-057 exceeded 0.78 μGal, 0.79 μGal, and 0.42 μGal, respectively. This testing scheme can be used as a reference for conducting acceptance testing of AGs in the future and obtaining absolute gravimetric measurements.

Based on the relative and absolute gravity measurements in the southern South-North Seismic Belt since 2015, we analyzed the dynamic change of the regional gravity field and its relationship with the Yangbi M_S6.4 earthquake that occurred on May 21, 2021. The results show that: 1) The regional gravity field changes are closely related to the Weixi-Qiaohou fault, which reflects the surface gravity field changes caused by the fault activity from 2015 to 2021; 2) The gravity field change related to the preparation of Yangbi earthquake has experienced the evolution process of " steady state - regional gravity anomaly - local gravity anomaly - four-quadrant distribution - large area positive anomaly - earthquake occurring in the reverse change process "; 3) The cumulative and differential change images of the gravity field show that there were significant gravity changes in the two years preceding the Yangbi earthquake, and the earthquake occurred in the high-gradient belt of gravity variation, the center of the four-quadrant, and close to the zero contour turn; 4) The dynamic evolution image of the gravity field can well reflect the precursory phenomena during the preparation for the Yangbi M_S6.4 earthquake. Based on the anomaly change of mobile gravity, a certain degree of medium-term prediction was made before the Yangbi M_S6.4 earthquake, especially the determination of strong earthquake location.