Based on strong motion acceleration records of Hubei Yingcheng M4.9 earthquake on 2019-12-26, we process the baseline correction and filtering and analyze the distribution characteristics of the ground motion. The results show that the peak ground acceleration (PGA) recorded in this earthquake attenuate rapidly with distance; the site effect, the hanging wall effect, and the rupture directivity effect cause the great differences among the ground motions. The data recorded at Yingcheng station are processed by rotating correction. There are obvious differences between the records along fault direction and those in perpendicular-to-fault direction and vertical direction, in which exists an analogous simple harmonic strong motion with a period of about 0.3 s, which is consistent with the focal mechanism mainly characterized by strike slip.
The 2011 Tohoku-Oki MW9.0 earthquake not only caused more than 5 m coseismic displacement and significant post earthquake deformation of the surface in Japan, but also caused significant far-field coseismic and post earthquake deformation in the eastern part of Chinese mainland. In this paper, using intensive GPS data observed from 1999 to 2017, we infer the results of far-field coseismic and postseismic displacements with high spatial resolution in eastern China. The results show that the 2011 Tohoku-Oki earthquake produced coseismic deformation of eastward movement in the east of 105°E in China, and considerable postseismic deformation in northeastern China and Shandong peninsula. The accumulated GPS postseismic displacement has exceeded its coseismic displacement. The observed far-field coseismic and postseismic deformation are helpful to maintain regional geodetic datum, and to provide a priori constraints for investigating the lithosphere and upper mantle rheology.
We analyze characteristics of present-day crustal 3D movement with GNSS data since 1999 and precise leveling data since the 1970s from Hainan island and the adjacent area. Combining these data with the horizontal movement field in the region of southeast Asia, we discuss how horizontal velocity in Hainan and the continental margin of the south China block(SCB) are influencedby surrounding tectonic plates. The results show that 3D movement of Hainan island is bounded with the Baisha fault, and the boundary of that in north island is Haikou-Tunchang line. The values of the east movement of SCB decrease from west to east, the rates of the epicontinental stations are smallest and their differences are smaller. The values of the south movement increase gradually from west to east. The velocities of stations at 23°~26° N(west of Taiwan island) are different from that of those stations on its north and south. The movement of SCB is affected by Indo-European collision and extrusion, the continental margin affected by movement of the Pacific Ocean and the Philippine sea plate, and the expansion of the south China sea(SCS). The Australia plate has less impact on the regional movement.
On 8 August 2017, a MS7.0 earthquake struck Jiuzhaigou county, Sichuan province, China. In this study, we use GPS, InSAR and strong motion data to invert the fault geometry and rupture model associated with the earthquake and analyze the cause of the earthquake. The results show that the Jiuzhaigou earthquake occurred on a blind strike-slip fault with strike 154° and dip 80°. The coseismic slip is dominated by left-lateral strike slip with a slight normal slip component and mainly locates at a depth of 2~12 km. The maximum slip is 1.6 m at a depth of 6 km. There is no slip on the subfault patches near the surface. The total seismic moment released in the Jiuzhaigou earthquake is 5.59×1018 Nm, corresponding to an MW6.44 event. We believe that the seismogenic fault is the hidden northern segment of the Huya fault.
The southern section of the Tangxi fault of the Taihang Mountains is studied by means of troughing, dating test, terrace survey and deformation measurement monitoring. The activity characteristics of the southern section of the Tangxi fault are analyzed and discussed. The results show that the Tangxi fault developed in the Middle Pleistocene and experienced many activities. The activity intensity in the southern segment of the Tangxi fault is relatively high,and the fault does not extend to the Late Pleistocene strata. The era of latest activity of the southern section of the Tangxi fault is the Middle Pleistocene. The results of vertical deformation monitoring of Xidaicun site in Tangxi fault (1999-2014) are abnormal. Based on the data of all monitoring points and regional neotectonic characteristics, the abnormality may reflect regional deformation in the working area, not caused by Tangxi fault.
In order to establish a high-precision slope displacement prediction model, we use phase space reconstruction(PSR) to transform the slope displacement time series data into multi-dimensional data. The wavelet kernel function is constructed to improve the support vector machine model and to establish the PSR-WSVM model. The model is applied to slope displacement prediction. The PSR-WSVM model prediction results are compared with the traditional support vector machine model(SVM), wavelet support vector machine model(WSVM) and phase space reconstruction-based support vector machine model(PSR-SVM) prediction results. The average absolute error is passed. Mean absolute error percentage(MAPE) and root mean square error(RMSE) accuracy evaluation indicators verify the feasibility of the PSR-WSVM model. The results of engineering examples show that the three precision evaluation indexes of PSR-WSVM model prediction result are better than the other three models, and the accuracy of slope displacement prediction has obvious improvement.
We process and analyze the repeated gravimetry network data of Hubei province and its adjacent area. 14 long-term and short-term gravity change maps are obtained from Sep 2016 to Sep 2019. We analyze the gravity changes characteristics before Yingcheng M4.9 earthquake on December 26, 2019. The results show that: 1) The Xiangfan(Xiangyang)-Guangji(Wuxue) fault is related to Yingcheng M4.9 earthquake. It is in the transition zone between positive and negative gravity anomaly. 2) There is an abnormal rise and fall of gravity before the earthquake. It occurs during the fall process. 3) The earthquake pregnancy spans a long period of time, which is similar to Zigui M4.5 and M4.1 earthquakes on October 11, 2018. The similarity may be related to the fact that the activity of active faults in Hubei and Hunan province is weak; their movement amount is small and their stresses are often hard to concentrate.
We combine ground geodetic data(absolute gravity, GNSS), surface and underground hydrological data, and GRACE satellite gravity data. Based on the long-term variation of absolute gravity at Jixian GNSS datum station in 20 recent years(1998 to 2018), we calculate and analyze the gravity effect caused by different physical signals, including the vertical displacement of the earth’s surface, groundwater and surface water load. Then, the characteristics of long-term gravity variation of each influencing factor are obtained, and the following conclusions are drawn through in-depth analysis and study: The long-term variation of absolute gravity at Jixian datum station from 1998 to 2018 shows a downward trend as a whole, and the change rate is about -1.64±0.53 μGal/a. The well water level data from 2004 to 2017 shows that the groundwater at Jixian GNSS datum station has an obvious downward trend, with a change rate of about -0.66±0.07 m/a, and the gravity effect is -1.94±0.22 μGal/a. It is the most important factor that affects the gravity change of this point. A comprehensive analysis of the long-term variation characteristics of the ground absolute gravity and other gravity effect factors shows that there is a gravity rise of about 0.43±0.58 μGal/a at Jixian datum station. It may be related to the upwelling of high-density matter at the top of the upper mantle in the capital circle area.
In this paper, based on the global atmospheric model and the data of Zhejiang regional meteorological station, the load deformation field and the change of gravity field caused by atmospheric pressure are calculated by the method of removing and restoring according to the load theory. The results show that the vertical deformation caused by atmospheric load in Zhejiang province reaches 12.1 mm, and the ground gravity change caused by atmospheric load exceeds 12 μGal. The influence of vertical deviation is small, and the atmospheric load has obvious annual periodicity and seasonality.
The study of the disturbance process of hydrologic load on crustal stress is helpful in clarifying the relationship between hydrologic load and seismic activity. Using the seasonal signal of GPS time series in Nepal, the seasonal three-dimensional displacement field and stress-strain field model in this region is constructed. The modulation effect of seasonal hydrological load on seismicity in this area is studied by combining rainfall and seismic catalogue. The results show that: 1) there is a strong spatiotemporal correlation between seasonal surface displacement and rainfall; 2) the rainfall in monsoon period disturbs the long-term movement trend of the fault and releases the Coulomb stress to a certain extent, thus inhibiting the seismic activity and affecting the time of the earthquake.
We study the temporal and spatial evolution characteristics of the low point of the daily variation of the geomagnetic vertical component before the Songyuan M5.7 earthquake. The results show that: 1) when the isoline of the low point time 0 h after the longitude effect is removed, the epicenter of the Songyuan M5.7 earthquake is located on the boundary of April 13 and near the boundary of April 24, respectively; 2) during the abnormal day(the geomagnetic vertical component day of the mainland of China), the daily deformation patterns in the region with positive and negative low point time after longitude effect removal are mainly W-shaped and V-shaped respectively; 3) during the two abnormal days of April 13 and April 24, there are high gradient zones with low point time after longitude effect removal in mainland of China, and the epicenter of Songyuan M5.7 earthquake is located at the edge of high gradient zone on April 13, and the east side of high gradient zone on April 24 respectively.
Based on the quaternion algorithm, we introduce the concepts of the conjugate and inverse of vectors and the Glassman product, which represents another multiplication of two vectors. The quaternion corresponding to a large arc on a sphere is the inverse of Glassman product of the unit vector, whose center points to the end of the large arc, and the unit vector whose center points to the beginning of the large arc. The quaternion corresponding to spherical angle is the inverse of Glassman product of the unit vector of normal plane of the final arc(toward the vertex) and the unit vector of plane normal of the initial arc (away from the vertex). It is easy to derive spherical trigonometry formulae using the quaternion algorithm, including sinusoidal and cosine formulae, and the first and second five elements formulae.
In this paper, we determine SWARM satellite orbits using the reduced-dynamic method, and estimate the receiver antenna PCO and PCV models based on the carrier phase residuals to verify their influence on orbit determination accuracy. The results show that when using PCO information, the accuracy of orbit determination is obviously improved, and the radial, along-track and cross-track RMSs are improved by 47%, 48% and 66%, respectively. After correcting the PCV effect, the POD accuracies in three directions are improved to the mm level. The SLR RMS statistics show that, considering the PCO and PCV, the average RMS of SWARM is 2.29 cm, which is very close to the post-scientific orbit. Finally, after comparing different PCV models, we infer that the 5°×5° PCV grid model is suitable for SWARM satellite POD.
Due to the small number and uneven distribution of tracking stations of BDS-2, GLONASS, Galileo satellites, it is necessary to obtain high-precision common parameters with GPS in the actual BDS-2/GLONASS/Galileo orbit determination process to improve orbit accuracy. In order to optimize the data processing strategy of joint orbit determination, it is necessary to analyze the influence of the common parameters in the joint orbit determination on the orbit. This paper analyzes the contribution of common station coordinates, tropospheric and receiver clock parameters, to multi-system joint orbit determination in the non-ionosphere combination from the theoretical point of view. Finally, we carry out single-system and multi-system joint orbit determination experiments. The experimental results show that the high-precision common parameters have a significant effect on the accuracy of the orbit determination of each single system. The accuracy of the orbit accuracy of the IGSO of BDS-2, GLONASS, and Galileo can be improved by almost 20%, and the orbit accuracy of the MEO of BDS-2 can be improved by almost 60%.
This paper analyzes the LEO constellation’s enhancement effect on GNSS’s precise point positioning(PPP), adopting mathematical simulation technology and taking the GPS system and the Iridium system as examples. Based on the emulational observation data of the GPS and Iridium, taking BJFS station as an example, pseudo- kinematic precise point positioning experiment is performed. The test results show that, compared with the GPS single system, the number of visible satellites of the GPS+Iridium dual system increases by an average of 1.5. The GDOP value and the PDOP value decrease by about 0.25. With Iridium enhanced GPS, the condition number of PPP filtration matrix reduces rapidly and the stability of PPP filtration is promoted; the positioning accuracy of the zenith U-direction, along with the three-dimensional positioning accuracy; the PPP convergence time is shortened by 30% or more and single-difference MW method is adopted to fix the PPP ambiguity. With Ratio =1.5, 3, 5 as an index of ambiguity fixed successfully, and compared with the emulational value of ambiguity, the time required for the first successful fixing of PPP ambiguity is shortened by 40% or more.
Based on the latest MGEX station that can receive the new signals B2a and B2(B2a+b) from BDS-3, we analyze the carrier noise ratio of the BDS-3 signal, multipath and the position dilution of precision of the satellite(PDOP). The results show that compared with GPS, the CNR B2(B2a+b)>B2a≈L5>B3≈B2b>B1≈L1>L2, multipath B2(B2a+b)<B2a≈L5<B3≈B2b <L2<L1<B1. The PDOP value of BDS-3 is similar to GPS, and the PDOP is significantly reduced after being composed of multiple systems with GPS.
Adopting natural earthquakes and artificial explosion waveform record events of Fujian region, through one dimensional discrete wavelet transform(DWT) and 4-layer wavelet packet transform(WPT) for signal decomposition, we use the extract to identify four waveform little potter characters: the wavelet energy than characteristics, wavelet packet energy than features, wavelet packet Shannon entropy, logarithmic of wavelet packet energy entropy.Inaddition, we extract the original waveform P/S seismic phase amplitude ratio.We use BP neural network to test the recognition effect of four kinds of wavelet characteristics and add the characteristics of P/S seismic phase amplitude ratio respectively. The results show that the wavelet energy ratio feature recognition is effective. The combination of P/S seismic phase amplitude ratio and wavelet packet logarithmic energy entropy has the best recognition effect, which can be considered as the identification criterion for the online automatic identification system of natural earthquake and artificial explosion.
Based on the refraction time-distance curve equation, we anayze the principle of common-receiver refraction stack imaging technology. The refraction wave of the 2D fault model is stacked in common midpoint domain and common-receiver domain respectively, and the actual 2D seismic data of Hexi corridor is processed comparatively. The results of model and practical application show that the common-receiver domain profile has higher lateral resolution than the common midpoint domain. This method, in combination with other data, can accurately determine the spatial location of fault points on active faults.
The microtremor noise data of 12 stations in western Inner Mongolia are used to calculate site response based on Nakamura noise spectral ratio method. The site responses of stations are classified into 3 categories according to the shape of site response curves. Site response is affected by topography, structure, base condition and so on. Comparing noise spectral ratio method with Moya method shows that the curve shapes of these two methods are basically consistent, only a few stations are significantly different. The results show most stations in western Inner Mongolia are in a good site platform situation, and site response curves are relatively flat, without obvious frequency amplification points.
This paper introduces the working modes of ML-1 frequency-stabilized laser. The results of single mode and two modes measurements are compared with those of the FG5X absolute gravimeter. We show that the working modes of ML-1 laser can effectively reduce the influence of temperature drift and time drift on absolute gravity observation. The red/blue separation indicates the laser drift. When the red/blue separation is large, it indicates that there is a large drift in the frequency-stabilized laser, which needs calibration.
In this paper, we carefully analyze the static and dynamic drift characteristics of four CG-5 gravimeters. We find that the static drift of CG-5 gravimeters increases linearly in one static test result. When we divide different time scales, there are still some differences in instrument drift rate in each time period. At the same time, the static drift rate varies over long periods of time. The drift rate of CG-5 gravimeters varies greatly with different measuring times. The drift rate of CG-5 gravimeters vary greatly when initially put into use, gradually decreases with time, and the final drift rate varies in a certain range. The dynamic drift rate of the four instruments is not closely related to the instrument space. The drift characteristics of each instrument show a relatively consistent trend in the long-term variation of static drift rate, in the dynamic test of uphill and downhill, and in the dynamic drift rate change process of each line in a single period. Based on the above, this paper uses the method of time-division adjustment to correct the drift of observation data. After drift correction, the data quality of each instrument and the whole system is improved.
