The full horizontal gradient (HGM) and the square root of the sum of the squares of the horizontal, vertical and diagonal components (HVDM) in Tibetan plateau and surrounding region are calculated using the discrete wavelet transformation. The results show as follows: 1) the higher HGM of the sum of the 4th and 5th order wavelet details appeared on the Nepal Himalayas, eastern Himalayan syntaxis (EHS) and the Altyn Tagh fault, which are the more active tectonic belts around Tibetan plateau. 2) The high HGM values of the Nepal Himalayas and the western segment of the Altyn Tagh fault and morphology of the higher HGM belts around the Tibetan plateau identify differences in crustal thickness and material properties of the lower crust and the uppermost mantle in the Tibetan plateau and the blocks surrounding it. 3) The high HVDM belts distributed on the Himalayas, EHS, the Altyn Tagh fault and the Longmenshan fault reveal the morphological characteristics of the tectonic belts around the Tibetan plateau. 4) The epicenter of the 2015 Nepal earthquake is located on the low value belt of the HGM distribution with high\|low\|high, as well as at the boundary of the high HVDM value. This earthquake resulted from the accumulated energy caused by convergence of the India\|Eurasia continental collision and accommodation of the released large\|scale strike\|slip faults
Velocity results from published papers, which are in different reference frame, are transferred into a self-consistent frame based on common GPS velocities of each result. We investigate the interseismic coupling of the rupture fault before the Nepal earthquake based on interseismic GPS velocities along a profile in N15°E direction, which runs across the rupture region of the 2015 Mw7.9 Nepal earthquake. We model the creeping fault as a planar semi-space dislocation embedded in elastic half-space, and invert the horizontal velocities to infer the preferred locking depth and slip rate. The preferred model indicates that interseismic deformation is induced by a fault dipping at 10°, buried at a depth of 22.5 km, with a slip rate of 19.0 mm/a. Then, near field coseismic displacements measured from GPS observations are presented. The largest horizontal displacement of 1.89 m was recorded at KKN4 in Nepal. Coseismic offset of 54 cm was measured in southern Tibetan plateau, which is the largest value measured in mainland China. The displacements decrease rapidly to less than 5.0 mm at GPS stations 400 km away from the epicenter. GPS derived coseismic displacements along the N15°E profile show that the offset near the fault trace is not the largest offset measured by GPS, indicating that the shallow part of the fault did not rupture during the Nepal earthquake. The horizontal coseismic offset profile can be modeled well using a buried rectangular dislocation model. Therefore, we infer the rupture fault of the Nepal earthquake may be the main Himalaya thrust (MHT), and the shallow parts did not rupture during the shake.
Based on previous research, we analyze seismogenic structure, the triggering of aftershocks by mainshock, and the subsequent distribution of aftershocks, on the basis of which we discuss the seismicity trends surrounding the Nepal earthquake. The preliminary study suggests that the main boundary fault is responsible for this event, belonging to low-angle thrust faulting. The spatial distribution range of aftershocks is basically consistent with source rupture area and pattern, characterized by a migration eastward in time sequence. Furthermore, both the earthquake events of Nielamu Ms5.3 and Dingri Ms5.9 may be consequences of the tectonic stress field changes caused by the mainshock, and do not belong to its aftershock. The most seismically dangerous area is in a certain segment between the mainshock and the Himalayan eastern structural syntaxis along the subduction zone of the Indian and Eurasian plates.
Using measurements from three national repeated gravity networks-the crustal movement observation network of ChinaⅠ, digital earthquake observation network of China, and the crustal movement observation network of China during 1998-2013, we obtain the annual gravity rate in Tibet and its vicinity. Based on the lake level change in Qinghai-Tibet Plateau, we estimate the gravity effects due to the continental water storage changes at each site. Finally, we obtain the spatial distribution of the long-term gravity changes in Tibet and its vicinity through spatial Gaussian filter with 50 km smooth radius. From our research we find: 1) The time series at typical gravity stations show a clear linear trend, which means the linear trend is the principal characteristic at those stations. The positive linear trend implies accumulated regional gravity changes in the past decades. 2) The long-term gravity changes in Tibet and its vicinity show uneven spatial distribution, which might be related with the complicated crustal deformation and geodynamical mechanisms in the Qinghai-Tibet Plateau. The Himalayan tectonic block shows a significant positive gravity annual rate, which might be related to underground mass redistribution and adjustment caused by continuous extrusional deformation between the Indian and the Eurasian plates. The positive gravity variations might indicate the stress and energy acceleration surrounding the locality of the earthquake due to the crustal deformation and medium changes during the process of earthquake preparation.
This paper analyzes the shortcomings and deficiencies of the conventional earthquake emergency command system. We highlight the composition, architectural design and main features of the earthquake emergency system made by the Earthquake Adminstration of Hubei Province. Then, we briefly describe the application of the earthquake emergency system in the Nepal 8.1 earthquake emergency work. Finally, combined with new technology and new ideas, we anticipate and discuss next steps in the development direction of the earthquake emergency system. Practice shows that the earthquake emergency system helps the earthquake departments establish a comprehensive, responsive and efficient operation of earthquake emergency command system. It also improves the ability to deal with the earthquake event for the earthquake departments. It has high practical value.
Many micro-small earthquakes occurred near the epicenter before the Zigui 4.5 and 4.7 earthquakes on Mar 27, 30 in 2014. The D-D location results showed these earthquakes distributed near the sub-fault of the west of the Xiannüshan fault (area one) and the north end of this fault (area two). According to spectral analysis of the near-field seismic wave and characteristics of the regional geology and tectonics, we believe that small earthquakes in the area one were mainly shallow collapse events and earthquakes in the area two were tectonics seismic events. Comparing the statistical results of the focal mechanisms parameters of 15 small earthquakes in the area two to focal mechanisms of the 3 main shocks in this area, it shows that both plane strikes are NNW and NE, and that the azimuth and dip of force axes (P and T axes) are also basically the same, i.e., wholly consistent with the orientation of the regional stress field. These results reflect that the two force patterns have some consistency, but that there were differences on the rapture mode, which may be related to the re-activity of Xiannüshan fault by the effects of the water in the Three Gorges reservoir.
Based on GPS velocity field data from 1999 to 2013, we calculate the train rate field and the Euler rotation vector of main blocks in Longmenshan and the surrounding area. Using these results as constraints, we calculate the slip rate and locking depth of the main active faults with the Rngchn program based on the Okada model, and then discuss regional tectonic deformation and strain distribution in the research area. Finally, we analyze the effect of the Wenchuan earthquake on the above process. The research shows that: most active blocks, such as east Bayan Har, northwest Sichuan and middle Yunnan, are moving to the southeast with a clockwise rotation at the same time. Due to the crustal strain absorption and adjustment of thrust belts such as the Longmenshan fault, the regional crustal deformation decreases gradually from the west to the east. The Wenchuan earthquake not only accelerated the motion of Bayan Har and northwest Sichuan block, but also enhanced the strike-slip and thrust movement of the Anninghe-Zemuhe-Xiaojiang fault and the Lijiang-Xiaojinhe fault.
For signal-in-space accuracy assessment of the BDS regional satellite navigation system, this paper analyzes the use of precise ephemeris algorithms for spatial signal evaluation and the projection principle of SISURE. Further, it discusses the parameters for BDS of different constellations. In the examples, this paper estimates the signal-in-space accuracy in BDS of various satellites, and finds that the average SISURE grated error reaches 1.54 m, and that there is still a gap between BDS and GPS. This paper also analyzes larger signal-in-space errors of some satellite components and finds some important conclusions.
Aiming at improving the limitations of existing GPS wave measurement technologies, a GPS wave measurement method using TRACK is presented| specifically, acquiring high-precision vertical displacement of carrier on sea surface via TRACK, then deriving the wave signal from the vertical displacement time series, estimating the signal power spectrum using periodogram method, and figuring out the wave elements. Using the measured data for experimental purposes, the results show that the differences of average wave height and average period are within 2 cm and 0.25 s compared with the results of wave gauge, confirming the feasibility of the proposed method.
In response to the limitations of traditional weighting methods for leveling-network adjustment in complex areas, this paper establishes a new standard of classification for elevation difference based on the relationship between the observation errors of elevation difference and the hypsography. The calculation formulae for all weights of elevation difference observations are deduced. Then the Helmert variance component estimation is reasonably introduced to match the relationship of weight ratio for elevation difference values. In the end, advantages of the new method were proven with an example
In this paper, experiments are conducted in the area of 500 kV and 220 kV high-voltage transmission lines to research the effect of high-voltage transmission lines on GPS observations. The results show that electromagnetic interference and radio interference caused by the high-voltage transmission lines have no significant effect on the internal noise of the GPS receiver. The high-voltage transmission lines significantly impact the multipath effects. The closer to the lines and the higher the voltage, the more serious were the multipath effects. The high-voltage transmission lines have no significant effect on the ability of the GPS receiver to capture the data, the stability of the receiver clock, signal-to-noise ratio of the L1 and L2 carrier, cycle slip of the observation data, and the accuracy of calculation of the baselines and coordinates.
Aimed at the vast network data of IGS, MGEX and iGMAS, a rapid data processing method of multi-GNSS zero-difference precise orbit determination is proposed. Then, the accuracy and time consumption of the ultra rapid orbit products are analyzed. The results show that the efficiency of data processing using multi-GNSS ultra rapid orbit products is obviously improved. It provides enough time for data generation and downloading, because less solving time is needed. Thus, the 24 h observation data can wholly participate in orbit determination, and the orbit determination accuracy of each satellite system is also improved to some degree
This paper introduces the time series prediction model of ionospheric VTEC improved by wavelet decomposition. The VTEC grid data released by IGS in 2013 are taken as experimental data to model point by point. Firstly, the VTEC series of 5 112 grid points are decomposed using db4 separately, then predicted using time series analysis, and finally reconstructed to predict the VTEC. The forecast bias and RMSE of the common prediction method and the improved method are compared. The result shows that the precision and the proportion of high accuracy using the improved method are better than the common prediction method. The improved method achieves the aim of raising accuracy.
〗Ionospheric delay is the main error of satellite measurement. As the precision of the traditional Klobuchar model is not high, this paper presents a new Klobuchar model that is designed to improve the precision of Beidou satellite navigation systems. We use a GIM model for CODE as a reference and a relax iterative search method to 〖JP2〗conduct case analysis, including the China region’s grid points and the observed data from nine stations. By comparing the two models, we find that the new model has a higher correction rate with respect to the broadcast model. Moreover, using the new model to forecast ionospheric delay within one week also has a better correction effect than the broadcast model. Statistical data further shows that the average correction precision improvement on grid points is from 67.89% to 78.44%, and the observed data of different stations from 69.81% to 82.34%.
〗In order to analyze the skewness of GPS time series data, a skewness factor MC is introduced for measurement as well as construction of the corresponding function in order to improve the detection range of the IQR law. We interpolate after rejecting the outliers, using the time series of the CHAN IGS station provided by Sopac experimental sequence, artificially adding different orders of magnitude and different densities of outlier. We confirmed that the IQR law considering skewness is more rigorous in algorithm and more effective in outlier detection than IQR law alone.
Taking the least squares surface fitting model as background field, and using accuracy measured data of the Nanning regional CORS network, we continue to correct the Klobuchar model of the initial phase, amplitude and night time delay values, in order to establish a Nanning region ionospheric delay model. The results show obvious improvement in the accuracy of the Klobuchar model.
Considering errors of distances, weighted total least squares regression is applied to estimate parameters of variogram model. According to variance-covariance propagation law, variogram values and distances after classification are found unequally accurate. Combined with two weighting methods of variogram values, the entropy weight method and number of points method, the weight method of distances derived by the variance-covariance propagation law is used to estimate parameters. Taking the power function model as an example, weighted total least squares regression is proven to be more reasonable and accurate by results of simulated and actual data.
The quaternion has been widely used in three dimensional space datum transformation, but its theoretical basis is not very clear. This paper studies some basic properties of the quaternion theory, and it proves that coordinate rotation transformation is equivalent to the orthogonal transformation of quaternion. Using the definition of basic quaternions, it establishes that all quaternions applied to coordinate rotational transformation are made by several basic quaternion’s Glassman product. At the same time, the theoretical relationship between quaternions and coordinate rotation matrix are given.
According to the phenomenon that a morphological filter erodes terrain excessively and the demand of seed ground points for region growing, a two-stage “rough-refined” filtering strategy is proposed. First, a rough digital elevation model (DEM) is obtained by applying a multi-scale morphological filter to airborne LiDAR data, which is called rough filter. Then, region growing is applied to gain refined DEM based on the seed ground points derived from the rough DEM. When tested against the ISPRS LiDAR reference datasets, the experiment shows that the proposed algorithm is highly adaptable to various landscapes in reserving the detail of terrain effectively, and also is more robust.
Multi-step prediction, a new algorithm based on ensemble empirical mode decomposition (EEMD) for dam deformation prediction, is presented. Firstly, starting from the time-frequency analysis, with the use of a collection of empirical mode decomposition, deformation time series are broken down into characteristic components of different frequencies. Secondly, run-determination act is used to reconstruct volatility components similar to high, medium and low ones. This is effective in centralizing model predictive feature information and reducing the difficulty. Finally, multi-step prediction model of the three is established separately and the predictive values are overlayed as the final prediction result. The calculation result is analyzed and compared with the AR model, BP neural network and SVM. At the same time, different prediction verification instructions are established to prove our algorithm. The results show that the prediction accuracy of EEMD is higher, it can guarantee better prediction of dam deformation in volatile periods| it is feasible to apply to dam deformation prediction.
Combined with the Logistic and Richards models, reference shifted-inverse power method translation right of the eigenvalues of the inverse power method and method of Logistic model and Richards model with different weight combination. Taking the South-Renmin station and Ludan village station of Shenzhen and the East-Four station of Changsha as an example, we use the new Logistic-Richards combination model of ground surface settlement during subway construction in fitting and prediction, and the superiority of the combination model is verified by the contrast.
The analytic expressions of principal strain and shear strain are deduced by quadrilateral law with three-dimensional deformation data. The horizontal and vertical strains of Wenchuan are calculated with the three-dimensional GPS data during 2005 to 2008. The results show that the horizontal principal strains of Wenchuan and Yingxiu are extrusion. The main vertical principal strain is positive in the southeast direction, but it is negative in the northwest direction. The main vertical principal strain is consistent with the observation that the surface is sinking in the southeast and uplifting in the northwest. The maximum principal strain is in Y (east) direction. The maximum shear strain is in XY (northeast) direction. Wenchuan is situated on the high gradient of the principal and shear strains, coinciding with the location of the earthquake
The kinematical parameters for 13 major global plates within NNR-MORVEL56 plate motion model, as well as their standard deviations, have been estimated in this paper, using velocities from 225 GPS sites with respect to ITRF2008. During the process of site selection, we obtained the second invariant strain rate (SISR) field of sites by the bicubic interpolation method according to the GSRMv1.2, supposing a site should be located in the rigid region if its SISR is lesser than 10－14/a. Given the effects of postglacial rebound on the sites’ velocity, this paper employed a quantitative calculation to the horizontal rate of the sites based on the ICE3G-VM2 model through the TABOO software, assuming that sites with a horizontal rate greater than 0.5 mm/a belongs to GIA region and should be eliminated. In the end of this paper, our results have been compared with the results by Altamimi and the MORVEL based on geological data respectively, showing that models established in this paper display a relatively high accuracy with the feasibility of site selection criteria adopted, and at the same time, the differences between these results and reasons causing kinematic deviation in several plates have also been illustrated.
This paper proposes a new model of landslide deformation prediction based on the grey artificial neural network, combining the data processing characteristics of the grey model and the artificial neural network, respectively. There are three kinds of forecasting model structure: series grey artificial neural network (SGANN), parallel grey artificial neural network (PGANN), and inlaid grey artificial neural network (IGANN). The landslide deformation time series is decomposed into trend item and random item in SGANN. The trend item of the deformation time series can be extracted by the grey model, using the artificial neural network to construct the nonlinear relationship between the deformation time series and the trend item. PGANN uses the grey model and the artificial neural network to predict separately, while the weight value of this model is subject to the required accuracy of the experiment. IGANN optimizes the topological structure of the neural network by adding a grey layer and grey model group, in order to reduce the randomness of the original monitoring data and to enhance the model robustness ability. The above three new models are employed to forecast the deformation time series data monitored at the Gushuwu landslide. The cases show that the grey artificial neural network model is valid and feasible in prediction of landslide deformation under complicated conditions.
Using drilling and shear wave velocity logging data collected from 43 engineering sites of seismic safety evaluation projects completed in Changzhi urban district, the structural models of shallow strata and shear wave velocity are built in terms of the Kriging interpolation, which is an unbiased evaluation method for non-uniform distribution of discrete data. The results show that the shallow strata and shear wave velocity structures present stronger laterally inhomogeneous features, and also indicate that the sedimentary deformation is obviously controlled by the hydrological environment as well as the main faults in Changzhi urban district and its adjacent areas.
This paper proposes a high accuracy prediction method for Earth polar motion parameters, using a dual differential least-squares (LS) and autoregressive (AR) model. Firstly, Earth polar motion parameters are calculated by dual differential methods to obtain differential results. The stationarity of differential polar motion parameters is improved. The LS method is utilized to fit the differential polar motion parameters to obtain the residual results. Secondly, the AR model is utilized to analyze the residual polar motion parameters. Thirdly, the extrapolated results of LS and AR model prediction results are combined to obtain the differential prediction results. Finally, the differential prediction results are calculated by inverse dual differential methods, to obtain the final prediction results. The proposed method is applied to the real Earth polar motion parameters prediction. The results show that 1 day’s PMX prediction accuracy is better than 0.25 mas, and 1 day’s PMY prediction accuracy is better than 0.2 mas. These results are compared with EOP_PCC results. It shows that this paper’s polar motion parameters short term prediction accuracy is close to EOP_PCC good prediction accuracy, and that 1 day’s prediction accuracy is a little better than EOP_PCC 1 day’s prediction accuracy.
Using three different strategies, we processed the land subsidence monitoring data collected by a mixed set of single-frequency and dual-frequency receivers installed in Nansha, Guangzhou, from July 1, 2012 to December 31, 2013. The result shows that during maximum solar sunspot cycle periods, ionospheric disturbances corrupted the precision of GPS data processing, even with the baselines less than 10 km. GPS measurement precision shows a standard deviation of about 5 mm, which is quite consistent with leveling results.
According to the deficiency existing in the EGM08 global gravity field model, a combined model is presented in this paper. The low and medium frequencies bands of the EGM08 model are substituted by a GOCE geopotential model, and very ultra-high frequencies signals are extended by a residual terrain model RTM. Simulant analyses show that the precision of height anomalies is widely improved by GOCE model, and the RTM’s contribution to height anomalies cannot be ignored. The GPS/leveling benchmarks tests show that the GOCE model’s contribution to height anomalies is up to 43%, and RTM’s contribution is 1 cm.
〗Although the sequence joint inversion is a priority method of joint inversion with gravity and seismic data, its theoretical basis is less comprehensive than the theoretical basis of synchronous joint inversion. So, we analyze the weak points of the sequence joint inversion, and make some improvements in the mesh mode of geological structure and constraints. Then we employ wavelet multi-scale analysis and quasi-BP neural network inversion to improve the resolution of the result and to accelerate convergence. The inversion of Suining-Aba in the Longman mountains shows that the inversion effect of this method is obvious.
High precision inter-satellite range rate is sensitive to mass anomaly in the Earth’s surface region. The function of the relationship between regional mass anomaly and spherical harmonic coefficients variation is deduced. According to this relationship, the influence of mass anomaly in different regions on gravity can be separated. The influence is simulated by adding mass variation of a certain height of equivalent water and analyzing the range rate residual of time-variable gravity field relative to background gravity field. The result shows that the influence of regional mass anomaly on range rate is limited spatially, and that range rate is very sensitive, and that the sensitivity is related to the content of mass variation.
A N-S trending profile has been set along the 106°E longitude and high-precision gravity data of this area was obtained for the first time. After a series of pretreatments and corrections, gravity anomalies of the profile are obtained. Analyses indicate that free-air anomaly of this profile is closely related to terrain. Bouguer gravity anomaly changes gently along the profile and relatively fast changes only occur in areas near the Gobi-Altai belt (GAB) and Haraa belt (HRB). The rapid gravity anomaly change may indicate a rapid change of deep structure, and such gravity anomaly change is not found around the Mongol-Okhotsk orogenic belt. The isostatic gravity anomaly of the profile is mainly negative, equilibrium has not been reached for most areas. The correlation between earthquake activity and isostatic anomaly of the profile is similar to research results of the northern North-South seismic belt.
〗This paper selects P, S wave arrival time difference Δt ≤ 14 s data, and calculates the Shanxi reservoir earthquake sequence seismic wave velocity using the multi-station method, combined with the characteristics of temporal and spatial distribution of seismic sequence and seismic structure. Analysis of the temporal and spatial distribution characteristics of wave velocity ratio sequence shows: 1) The seismic wave velocity ratio in Shanxi reservoir is 90% concentrated in 1.66-1.75, with an average velocity ratio of 1.70. 2) Shanxi reservoir earthquake sequence comprises a plurality of seismic activity. Each group of seismic velocity ratio starts by showing a rapid decline| after a phase of wave velocity ratio showing changes slowly rising. Wave velocity ratios between every two groups of earthquakes generally show a gradually increasing trend. Variation characteristics of wave velocity ratio in Shanxi reservoir earthquake sequence can be summarized as “drop-rebound-a group of earthquake”. 3) There is some relationship between the wave velocity changes and epicentral location. As the earthquake migrates to the new position, the initial several seismic wave velocity ratio is relatively large, and then the velocity ratio gradually reduces. 4) Along the depth direction and along the Shuangxi-Jiaoxiyang fracture direction, wave velocity distribution is not uniform. Wave velocity ratio is relatively small in the northwest segment of the Shuangxi-Jiaoxiyang fault submerged in the reservoir| wave velocity shows the most complex variation in the southeast segment of Shuangxi-Jiaoxiyang fracture. Located in the south bank of the reservoir, there are two transition regions of high value and low value wave velocity ratios. An ML≥4 earthquake occurred in the transition region at a 5-8 km depth.
This paper introduces the signal characteristics and the observed characteristics of continuous tremor waves in continent seismic observations. On the basis of identifying and extracting principles of tremor wave signals, improving the signal to noise ratio, reducing the analysis time scale, referencing international intermittent tremor positioning methods, improving the methods of signal identification, processing and positioning methods, we propose technological approaches and processes for positioning these kinds of signals. Further, we apply it to several tremor wave signals caused by typhoons in mainland Chinese seismic observation for positioning and effect testing. Results show that these technological approaches and processes are viable and that the positioning results are reasonable and believable.
On the basis more than ten absolute gravity values of the Himalaya project in the north and the south segments during 2011-2013, gravity dynamic variations are obtained according to the recalculated one-degree term of chromatic polynomial of gravimeter in the network of Gansu, Ningxia and Hexi. The results show: 1) Gravity variation is fairly dramatic in the Qinghai-Tibet plateau, which reflects tendency change on large spatial scales in the process that deep material moves to the northeast. 2) One-degree term of chromatic polynomial remains stable with respect to LCR-G and Burris| CG-5 decreased gradually (it should be calibrated according to the absolute values). 3) A general tendency of change of gravity variation after we used absolute values to calibrate the one-degree term of chromatic polynomial is consistent with long baseline calibration, data analysis is more reliable which is decreased.
This paper compares the full-scale verification method with the decimeter verification method, which are used for the verification of levelling staff. By using a paired-samples t test, we compare the results obtained by the two verification methods, and evaluate the repeatability and reproducibility of the results. The results obtained by the two verification methods show no significant differences| the reproducibility error occurred in both verification methods and the difference which occurred in the comparisons obtained by the two verification methods are of the same order of magnitude.
This paper presents an approach to store earthquake big data based on Hbase. We do so by setting up a test platform, Java language development test program, and MySQL in storage, query and structured and unstructured data for comparative testing of performance. The results show that, compared with the relational database MySQL, Hbase accesses earthquake data consuming less data volume over the long term, and that its performance is more significant.
Calculating travel time of seismic wave is an important part of the fields of seismology and seismic exploration. It is widely used for prestack migration, velocity analysis, seismic tomography, earthquake location, and so on. Analysis of the examples and effects of ray paths and travel times by applying the Ronge-Kutta ray tracing method, and comparing the results of the Ronge-Kutta ray tracing simulations and the effect of hodograph by eikonal equation calculated in several typical geological models of seismic exploration. Simulation results verify the stability of the eikonal equation finite-difference method in the calculation of travel times and the implementation of Ronge-Kutta ray tracing method. The study also shows that the Ronge-Kutta ray tracing method in complex structure region seismic ray paths and travel times calculation gets better simulation results.
The background noise level in seismic frequency band (200~600 s), sub-seismic frequency band (1-6 h) and tide frequency band (period>6 h), based on one year continuous observation of gPhone gravimeter at Taiyuan station of the crustal movement observation network of China (CMONOC), are investigated using a numerical analysis method, and they are compared with the noise level of other superconducting gravimeters (SG). It is found that the seismic noise magnitude (SNM), sub-seismic noise magnitude (SSNM) and tidal noise magnitude (TNM) of the gPhone gravimeter are 3.641, 4.659 and 5.359 respectively. The SNM and SSNM of the gPhone gravimeter are higher than that of SG, but when the frequency is below 0.8×10-4 Hz, the noise level of the gPhone gravimeter is lower than the new low noise level (NLNM). The Earth’s free oscillations excited by Chile Mw8.1 in 2014 are analyzed, and it is found that although the noise level of the gPhone gravimeter is higher than that of SG, the signal of oscillations can still be observed clearly. This means that the gPhone gravimeter is not only suited for researching tidal and sub-seismic modes, it also can be used for obtaining free oscillations signal in seismic frequency band.
We did tidal analysis and extracted gravity residual from continuous gravity records of gPhone meters (serial number 109 and 118) at Shisanling seismic station from April to August in 2013. The results showed the gPhone meters successfully detected the gravity variations at μGal level, which are caused by rainfall| the delay time of positive correlation between the 2nd-order curve fitting residual gravity of gPhone data and the static water level of Shahe seismic station (15 km from Shisanling seismic station) is about 4 d. Such a positive correlation indicates that the hydrology records are very important in the explanation of the observed gravity data. Therefore, to increase the processing accuracy of gravity data, it is necessary to add groundwater level observations to the continuous gravity observation network of our country.
〗In this paper, a new algorithm of principal component analysis (PCA) is proposed to extract the zero drift and the solid Earth tide from static relative gravimetric data, as observed by CG-5 relative gravimeter from Aug 15 to Aug 23, 2014. The results of the linear drift extracted by PCA are very consistent with those calculated by the least squares linear fitting method, and the differences only reach to 10-2 μGal/d order of magnitude. The statistical results of the solid earth tide extracted by PCA are quite consistent with results derived from the solid earth tide correction provided by CG-5 gravimeter internal software. The statistical results of the differences of the two methods are both less than 8 μGal, and the RMS for 9 d are all less than 5 μGal.
