Study on the Cap Rock Deformation of Hutubi Underground Gas Storage by GPS Observations

The deformation responses of surface cap rocks of Underground Gas Storage( UGS) in Hutubi,Xinjiang during gas injection and production were investigated with the GPS data recorded by the deformation monitoring network,which includes 13 observation sites. The time series of three-dimensional deformation of the surface cap rocks was obtained in the UGS operation process,and the deformation signals in different phases were identified by combining the GPS data with wellhead pressure data. The results show that the respiration response of surface cap rock deformation is obvious during gas injection and production of UGS,and the surface deformation due to a 1MPa change of wellhead pressure is 1. 02 mm in gas injection and 1. 24 mm in gas production horizontally, and- 1. 11 mm in gas injection and 0. 86 mm in gas production vertically.

Characteristics of regional crustal deformation before 2016 Menyuan Ms6.4 earthquake

On January 21, 2016, a strong earthquake with a magnitude of Ms6.4 happened at Menyuan,Qinghai Province of China. In almost the same place, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. In this paper, we analyze the characteristics of regional crustal deformation before the 2016 Menyuan Ms6.4 earthquake by using the data from 10 continuous Global Positioning System(GPS) stations and 74 campaign-mode GPS stations within 200 km of this event:(a) Based on the velocity field from over ten years GPS observations, a regional strain rate field is calculated. The results indicate that the crustal strain rate and seismic moment accumulation rate of the QilianHaiyuan active fault, which is the seismogenic tectonics of the event, are significantly higher than the surrounding regions. In a 20 km × 20 km area around the seismogenic region, the maximum and minimum principal strain rates are 21.5 nanostrain/a(NW-SE extension) and -46.6 nanostrain/a(NE-SW compression), respectively, and the seismic moment accumulation rates is 17.4 Nm/a. The direction of principal compression is consistent with the focal mechanism of this event.(b) Based on the position time series of the continuous GPS stations for a time-span of about 6 years before the event, we calculate the strain time series. The results show that the dilatation of the seismogenic region is continuously reduced with a "non-linear" trend since 2010, which means the seismogenic region has been in a state of compression. However, about 2-3 months before the event,both the dilatation and maximum shear strain show significant inverse trends. These abnormal changes of crustal deformation may reflect the non-linear adjustment of the stressestrain accumulation of the seismogenic region, when the accumulation is approaching the critical value of rupture.

Probing the interseismic locking state of the Xianshuihe fault based on a viscoelastic deformation model

The interseismic locking state of tectonic faults is essential for regional seismic hazard assessments.However,it is challenging to obtain this parameter reliably due to the weak deformation and complex model configurations.To better probe the fault locking state,more reliable physical models and well-covered observations are required.Here we investigate the locking state of the Xianshuihe fault based on a new-developed viscoelastic deformation model.Meanwhile,we combine GPS velocities from 13 new near-field stations and existing stations in this region to improve the spatial resolution.Similar to the theoretical predictions,our results indicate that the elastic model will clearly overestimate the fault locking depth and seismic moment accumulation rate,and the fault slip rate inferred from the elastic model is slightly lower than that from the viscoelastic model.Relying on the locking distribution inferred from the viscoelastic model,we identify four potential asperities on the Xianshuihe fault.More importantly,we find a clear spatial correlation between the fault locking distribution and the rupture extent of historical earthquakes,which indicates that the fault locking state may control the rupture extent and thus the magnitude of earthquakes.In addition,our results show that the 2022 M6.8 Luding earthquake only ruptured the south part of a potential asperity,and the accumulated energy in the northern unruptured area is equivalent to an Mw6.9 earthquake,where the seismic hazard deserves special attention.

Precise orbit determination for LEO satellites:single-receiver ambiguity resolution using GREAT products

In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites.The GNSS-based Precise Orbit Determination(POD)will be exclusively performed to achieve this goal,where the Integer Ambiguity Resolution(IAR)plays a key role in acquiring high-quality orbits.In this study,we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations.We perform ambiguity-fixed LEO POD for four typical missions,including Gravity Recovery and Climate Experiment(GRACE)Follow-On(GRACE-FO),Swarm,Jason-3 and Sentinel-3,using the Uncalibrated Phase Delay(UPD)products generated by our GREAT(GNSS+REsearch,Application and Teaching)software.The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits.There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias(OSB)and Integer Recovery Clock(IRC)products,indicating the good-quality of UPD products we generated.Compared to the float solution,the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites.Meanwhile,the benefit can be observed in laser ranging residuals as well,with a Standard Deviation(STD)reduction of 3–4 mm on average for the fixed solutions.Apart from the absolute orbits,the relative accuracy of the space baseline is also improved by 20–30%in the fixed solutions.The result demonstrates the superior performance of the ambiguity-fixed LEO POD,which appears as a particularly promising technique for POD of future LEO constellations.