Gravity variation before the Akto Ms6.7 earthquake, Xinjiang

The relationship between gravity variation and the Akto Ms6.7 earthquake on November 11, 2016, was studied by use of mobile gravity observation data from the China continental structural environmental monitoring network. The result revealed that before the Akto earthquake, a high positive gravity variation was observed in the Pamir tectonic knots region (within a maximum magnitude of approximately +80 microgal), which was consistent with the existing knowledge of gravity abnormality and the locations of strong earthquakes. In view of the recent strong seismic activities in the Pamir tectonic knots region, as well as the strong upward crust movement and compressive strain, it is believed that gravity change in the Pamir tectonic knots region reflects the recent strong seismic activities and crust movement

Seasonal gravity changes estimated from GRACE data

Since 2002, the GRACE program has provided a large amount of high-precision data, which can be used to detect temporal gravity variations related to global mass re-distribution inside the fluid envelop of the surface of the Earth. In order to make use of the GRACE data to investigate earthquake-related gravity changes in China, we first studied the degree variances of the monthly GRACE gravity field models, and then applied decor-relation and Gaussian smoothing method to obtain seasonal gravity changes in China. By deducting the multi-year mean seasonal variations from the seasonal maps, we found some earthquake-related gravity anomalies

Gravity variation in the Tibet area before the Nepal Ms8.1 earthquake

This research utilized two periods of gravity monitoring results from 2010 to 2013 from the Continental Tectonics Environmental Monitoring Network of China, analyzed the correlation between gravity variation in the Tibet area and the Nepal Ms8.1 earthquake, and investigated the gravity variation mechanism in combination with the crust vertical movement and horizontal strain field observed by Global Positioning System (GPS). The research results indicated that (1) the gravity variation exhibited apparent characteristics of a positive anomaly and high gradient zone in the Himalayan frontier. This observation is consistent with the existing recognition of the gravity anomaly and occurrence regularity of a strong earthquake; (2) the gravity variation exhibited apparent consistence with the spacious distribution of the vertical movement and the horizontal deformation field in that area. The crustal vertical movement was not the direct cause leading to the gravity variation. It is assumed that the crust stress–strain accumulation in the Qinghai–Tibetan Plateau and its adjacent areas is the important factor that resulted in the variation of gravity

Long-term gravity changes in Chinese mainland from GRACE and ground-based gravity measurements

A long-term (9 years) gravity change in Chinese mainland is obtained on the basis of observations of the ground-based national gravity network. The result shows several features that may be related to some large-scale groundwater pumping in North China, glacier-water flow and storage in Tianshan region, and pre-seismic gravity changes of the 2008 Ms8.0 Wenchuan earthquake, which are spatially similar to co-seismic changes but reversed in sign. These features are also shown in the result of the satellite-based GRACE observation, after a height effect is corrected with GPS data

Gravity inversion of deep-crust and mantle interfaces in the Three Gorges area

To better understand the heterogeneity of deep-crust and mantle interfaces in the region of the Three Gorges, China, we used the Parker-Oldenburg iterative inversion method to invert existing Bouguer gravity data from the Three Gorges area (1 : 500000), a new gravity map of the Three Gorges Dam (1 : 200000), and the results of deep seismic soundings. The inversion results show a Moho depth of 42 km between Badong and Zigui and the depth of the B2 lower-crustal interface beneath the Jianghan Plain and surrounding areas at 21–25 km. The morphology of crustal interfaces and the surface geology present an overpass structure. The mid-crust beneath the Three Gorges Dam is approximately 9 km thick, which is the thinnest in the Three Gorges area and may be related to the shallow low-density body near the Huangling anticline. The upper crust is seismogenic, and there is a close relationship between seismicity and the deep-crust and mantle interfaces. For example, the M5. 1 Zigui earthquake occurred where the gradients of the Moho and the B2 interface are the steepest, showing that deep structure has a very important effect on regional seismicity

Establishment of Absolute Gravity Datum in CMONOC and Its Application

The high accuracy absolute gravity datum covered the Chinese mainland area is established by using absolute gravity measurement data of one hundred stations in CMONOC(Crustal Movement Observation Network of China), the accuracy of each station is better than 5.0 μGal/a. The high accuracy gravity datum can be used for relative gravity measurements in adjustment, and the real gravity value can be determined from relative gravity measurement data of adjustment by using the gravity datum to avoid distortion of the real figure of gravity change. The trend of absolute gravity change from several observations at Chengdu station shows that the secular trend of gravity change is larger than 5.01±0.7 μGal/a, which is probably caused by the distribution of mass below the earth. The rate of land subsidence of Wuhan area is 3.27±0.65 mm/a determined from combined long-term absolute gravity measurements and GRACE satellite data according to the two system difference

Temporal variation of gravity-field in North China before and after the 2011 Japan Mw9.0 earthquake

Abstract:By using absolute and relative-gravity data recorded by the gravity network in North China, we obtained some large-scale and high-spatial-resolution images of gravity variation in this area for the first time. By analyzing these images, we found that the gravity in Liaodong peninsula area showed an obvious increase of 80 × l0−8ms−2 during about one- and-half year before the 2011 Japan Mw9.0 earthquake, and a rapid decrease after the earthquake. This gravity variation is similar to that observed previously for the 1976 Tangshan M7.8 earthquake

High-Accuracy Quasi-Geoid Determination Using Molodensky’s Series Solutions and Integrated Gravity/GNSS/Leveling Data

This study presents a methodology for constructing a quasi-geoid model with millimeter-level accuracy over the Shangyu area in China, following the guidelines of the International Association of Geodesy Joint Working Group 2.2.2, known as “The 1 cm geoid experiment”. Our approach combines two steps to ensure exceptional accuracy. First, we employ Molodensky’s theory to model the gravity field, accounting for non-level surfaces and considering complex terrain effects. Through an exhaustive analysis of these influential factors, we implement a comprehensive suite of applicable formulae within Molodensky’s series solution, enabling a thorough assessment of their impacts on height anomalies within the gravimetric quasi-geoid model. Second, we utilize a hybrid method that involves a multi-surface function using the least-squares method and a robust estimation technique. This approach enables the interpolation of quasi-geoid heights by incorporating ellipsoidal and leveling normal heights, as well as gravimetric quasi-geoid data. Through a numerical example, we demonstrate the efficiency of our solution concept, achieving an accuracy of 0.79 cm compared to independent global navigation satellite system (GNSS)/leveling measurements. By developing this methodology, our study contributes to the advancement of geodesy research and provides a valuable methodology for creating highly precise quasi-geoid models in geodetic applications