23 January 2017, Volume 37 Issue 2
-
Select all|
-
jgg. 2017, 37(2): 111-115.
Fangxian basin is steep in the south and gentle in the north, where Paleogenestrata developed well and pre-Quaternary strata tilts to the south. The normal faulting of Qingfeng fault zone, which is the south boundary of this basin, is obvious in Paleogene. Normal faulting of the NE trending Baihe fault and sinistral faulting of the NW trending Ankang-Fangxian fault control the extent of the Qingfeng fault and the EW boundary of this basin. Fangxian basin, which has undergone tension, compression and diverse settlement is a typical half-graben rifted basin. The hot spring groups are still developing, and moderate earthquake activity occurs in the basin.
-
jgg. 2017, 37(2): 116-121.
Based on both remote-sensing interpretation and field survey, we obtain some data about fault activity, terrace and planation of Fangxian basin and discuss the neotectonics. The preliminary analysis indicates that the fault inside basin is active in the early Quaternary but less active in late period. The boundary fault has strong activity in the late Quaternary with normal faulting, which is charcterized by extensional tectonic environment of uplift background. The characteristic of neotectonic activity presents different uplift between north and south, and the Cenozoic stratum all dips to south.
-
jgg. 2017, 37(2): 122-126.
On the basis of field geology survey and optically stimulated luminescence (OSL) dating, the geometrical structure and quaternary activity of the Yunyang basin segment of Yunyang-Yunxi faultshave been studied. The results show that there are huge differences between the edge and inside of the Yunyang basin in fault structure; the secondary fault on the basin edge is a wider dip-slip reverse fault, while the other secondary fault inside of the basin is a normal dip-slip fault, and has more stronger activity. The maximum fault displacement is about 20 cm; the sediment’s age (OSL) of the top failure point is 134.99±15.52 ka and 160.95±16.88 ka. This indicates that the last fault active period is in the late Pleistocene.
-
jgg. 2017, 37(2): 127-131.
The characteristics of the Hanjiang river terraces in Yunyang part are investigated in the field work. With geological, geomorphological and Quaternary chronological data, we infer that T1-T5 terraces were respectively formed in Holocene-late Pleistocene (about 25 ka B P), the late Pleistocene (about 67 ka B P), the early late Pleistocene-the end of middle Pleistocene (about 128 ka B P), the early middle Pleistocene-the late early Pleistocene (about 1 344 ka B P), no later than early Pleistocene. Horizontal contrast of terraces show activities of Liangyun fault make the vertical differences, indicating uplift between the T3 and T2 terraces from Wufeng, Qingqu and Yunyang basin. We suggest the age of faulting is the end of middle Pleistocene-the early late Pleistocene according to the forming age of the T3 and T2 terraces. The average uplifting rate of Hanjiang terrace in Yunyang part since the early Pleistocene is about 0.052 mm/a, which shows that the uplifting rate and magnitude is weaker than that in Qingling mountain. The main reason may be that Yunyang is located in the southern margin of Qinling mountain but not the center raising area.
-
jgg. 2017, 37(2): 132-136.
In this paper, multi-source remote sensing data are used to study the method of faults extraction, taking the central water source area of middle route of south-to-north water diversion project as an example. The multi-source remote sensing data includes medium-resolution optical images, high-resolution optical images, SAR images and DEM. In order to make full use of the penetration capability, spectral information and spatial geometry of the multi-source remote sensing data, the image enhancement, image fusion and three-dimensional terrain analysis, etc. are used to highlight the image flag of the faults. By the interpretation of multi-source remote sensing data and the field survey, the geometric distribution of the three major faults in the target zone are identified. It provides the reference for active fault detection and seismic hazard assessment in this area.
-
Seismic Activity Characteristics in the Early Second Phase of Water Storage of Danjiangkou Reservoirjgg. 2017, 37(2): 137-141.
After the second phase water storage in the Danjiangkou reservoir, according to the monitoring results of seismic network from 2013 to 2015, reservoir earthquakes are mainly either microseismic or ultra-microseismic. The epicenter location cloddy or banded together in five concentration areas every year. There is no apparent migration phenomenon along with the change of reservoir water level. Earthquake intensity and frequency in Dan reservoir are higher than Han reservoir. Earthquakes in Dan reservoir are mainly reservoir-induced, while the Han reservoir earthquakes combine reservoir-induced earthquakes with other types of untectonic earthquake.
-
jgg. 2017, 37(2): 142-145.
From the digital waveforms recorded from 2013 to 2015 by the digital seismic network of the core water source area for the central line project of the south-to-north water diversion, we select the digital waveforms of 141 earthquakes with ML≥1.5. The Q values of the structure beneath the core water area are calculated by analyzing seismic waveforms using Atkinson’s method. The results show that the average Q value depends on frequency by Q=146.0*f(0.770 3), and this moderate Q value indicates that this region is in anactive tectonic period at present.
-
jgg. 2017, 37(2): 146-148.
This paper mainly describes the shallow seismic reflection exploration of the Yunxi basin, using the results of seismic emission to determine the fault location and structural characteristics, which is based on the preliminary detailed geological survey. The fault distribution of the fault zone and its exact location is of great significance to the seismic safety system construction project of the middle route of the south to north water transfer project.
-
jgg. 2017, 37(2): 149-153.
In this paper, the truncated error of the earth gravity model is analyzed with RTOD simulation experiments, using the space-borne GPS observation data from several LEO satellites at different orbit heights. The optimal degrees and orders of the earth gravity model are chosen to match with RTOD solutions about 1.0 m using pseudo-range measurements and 0.5 m using carrier-phase measurements. Finally, this method is tested using other space-borne GPS data from CHAMP and TerraSAR-X satellites. The results show that our method can determine the optimal degree and order of the earth gravity model in RTOD, without the need of precise satellite orbit parameters. It is convenient to be applied to satellite missions for RTOD.
-
jgg. 2017, 37(2): 154-159.
This paper compares and analzes different regularization algorithms and parameter selections methods applied to the downward continuation of airborne gravity gradient data. Validation is achieved by comparing the results of the numerical simulation with those directly calculated by EGM2008. The numerical results show that a combination of the truncated singular value decomposition (TSVD) regularization method and the generalized cross validation (GCV) parameters selection method is most robust, and that this combination method is preferable to the other methods with respect to accuracy and stability.
-
jgg. 2017, 37(2): 160-162.
In an approximately 3 000 km2 hilly and semi-mountainous area of South China, 269 gravity points are measured to compare accuracy through various modelling types, algorithms and resolutions. Finally, the Bouguer gravity model anomaly model is calculated by the direct modeling method, and the accuracy was 1.7 mGal after the external coincidence test.
-
jgg. 2017, 37(2): 163-168.
Both observation vector and coefficient matrix contain errors in the crustal deformation problem, so total least squares collocation (TLSC) is studied. Then, we give the specific formula for determining parameters and the iterative algorithm under the generalized total least squares principle. Simulated horizontal crust deformation and the actual data from 2009 L’Aquila Italy earthquake are analyzed using total least squares collocation and least squares collocation. The experimental results show that the two methods are the same in the analysis of crust deformation, and this is given theoretical support in the article.
-
jgg. 2017, 37(2): 169-175.
For complicated types and distribution of the aftershock focal mechanism solutions，we give a concrete thought of inverting stress by aftershock focal mechanism with human factors as little as possible，according to the characteristics of ZMAP package.Based on aftershock focal mechanism solutions of the 1994 Northridge earthquake，using the stress tensor inversion method by Michael to analyze the tectonic stress state and its distribution in source region and preliminarily discuss the variations of stress state and its links to structure.The results show that the maximum principal stress in source region is nearly horizontal and trends NNE-SSW，which is an explicit characteristic of tectonic stress in Northridge earthquake source region.After Northridge earthquake，tectonic stress in deep and shallow area of source region are not entirely consistent.Even though the maximum principal axis is NNE both in deep and shallow area，the stress regime are thrust-faulting regime in deep area and strike-slip regime in shallow area.And the inversion result of deep data is consistent with region tectonic stress field.At same time，the difference of stress between deep and shallow area in source region is probably related to earthquake structure and movement mode of the Northridge earthquake with a stress regime of thrust-faulting.After the earthquake occurred, stress continued to release and blind fault kept on with thrusting movement under the action of regional tectonic stress. The thrusting movement of fault caused several thrusting earthquakes and stress state in deep area has no significant change. The thrusting movement of Northridge fault probably causes variations of stress and fault’s movement in the shallow area of source region.
-
jgg. 2017, 37(2): 176-181.
We take the GPS stations speed field in the Sichuan-Yunnan region as constraints and combine them with the known situation of fault distribution in the study region. Then, by using the Euler vector calculation and reversed Euler vector calculation methods, we get the Euler vector of each sub block. We make further adjustments to the Sichuan Yunnan region of sub blocks. We make a 1°×1° grid interpolation for the region, and reverse the long-term movement direction and speed of each sub block by using the Euler vector of each sub plate. With regard to the boundary of neighboring blocks, combining the Euler vector of respective blocks, we calculate the speed of the same point in the two blocks and subtract. Then we analyze the current rate of the main fault region.
-
jgg. 2017, 37(2): 182-186.
Theoretical precision of scanning points is analyzed and some key techniques, such as point cloud data acquisition and point cloud data preprocessing are discussed with an example of a landslide in Sichuan Lixian. Then a very intuitive and comprehensive landslide deformation analysis method is presented in this paper. Furthermore, a new method of extracting the geometric features of telegraph poles and tree trunks in the landslide area is presented in order to make the best of non-ground point cloud data.
-
jgg. 2017, 37(2): 187-191.
The accuracy of ERP solved by GPS technology is influenced by the selection of the station, the structure of the network and other factors. Accordingly, GPS data from IGS stations is downloaded to calculate ERP with a control variable method in order to analyze the effect of the number of stations and observation arcs on the accuracy of these parameters. The research shows that these two factors have a great impact on calculating ERP. In order to achieve optimum calculation efficiency and calculation precision, appropriate observation arcs should be selected according to the different station numbers.
-
jgg. 2017, 37(2): 192-195.
Three kinds of mapping functions such as Neill mapping function (NMF), Vienna mapping function1 (VMF1) and global mapping function (GMF) are introduced in this paper. The two indexes: baseline repeatability and standard deviation of the mean value for GPS baseline quality assessment, are discussed. According to the observation data of the IGS station in China, the data processing results based on GAMIT are used to research and analyze the influence of these three kinds of mapping functions on GPS baseline repeatability and standard deviation of the mean value. The results show that the calculation accuracy of dynamic mapping functions is higher than empirical mapping functionsin GPS baseline processing.In the solution of baseline repeatability, the VMF1 model is better than GMF model, but the GMF model is better in calculation of standard deviation of the mean value.
-
jgg. 2017, 37(2): 196-199.
The authors apply least-squares variance component estimation to evaluate unknown parameters of five different elevation-dependent stochastic models with double differenced GPS observables, and then use negative variance components as indicators to detect the applicability of models. Afterwards, the tangent, cosine,exponential function and the identical weight models are compared by calculating the baseline components. Test results indicate that the positioning accuracy and efficiency are dependent on elevation, and that one should choose the realistic stochastic model.
-
jgg. 2017, 37(2): 200-204.
Using GNSS and radiosonde data, a new inversion method is presented for troposphere refractivity index. A layered profile inversion model of parameters of refraction index above stations is constructed by combining radiosonde data and the high accuracy ZTD(zenith troposphere delay), which we estimate directly by GNSS observations of stations. Based on measured data from BJFS(Beijing station), WUHN(Wuhan station), WIND(Windhoek station) and DARW(Darwin station), this paper has accomplished corresponding calculations and validation. Eventually, the result shows that the new inversion model method and inversion model based on radiosonde data has the same accuracy, and their accuracy is even better compared with the inversion model of Hopfield. Furthermore, the new method is easy to calculate, and observations from radiosonde are greatly reduced when the new model is established.
-
jgg. 2017, 37(2): 205-208.
Triple-frequency GNSS observations with different frequency combinations are used to obtain ionospheric TEC. Corrections to hardware delay are made using the product provided by IGS. The results show that TEC offsets using observations of different frequency combinations are significantly reduced after applying IGS hardware delay corrections. Furthermore, a method for producing the final TEC is proposed.
-
jgg. 2017, 37(2): 209-214.
BDS/INS deep integration navigation,by using INS-aided BDS acquisition and carrier tracking,has been shown to improve navigation performance under low signal-to-noise ratio and high dynamic situations. It is important to develop the research on BDS/INS deep integration navigation with application of the BDS system. In this paper, we investigate the mechanism and performance evaluation criteria in BDS/INS deep integration navigation. The deep composite structure design is given and the entire performance is simulated on a software receiver. The simulation shows that this technique is effective and useful for actual engineering applications.
-
jgg. 2017, 37(2): 215-220.
To improve the predictive accuracy of Beidou satellite clock bias (SCB), it is necessary to adopt a proper method of data quality control to preprocess SCB. The phenomena consisting of phase jumps, outliers, and missing data exist in long term Beidou SCB sequence. Considering all these factors, a data quality control method for the Beidou-2 SCB series is proposed. The method is as follows. First, identify clock jumps through frequency sequence. Next, use threshold to get rid of abnormal data segments and combine median absolute deviation (MAD) and Baarda to detect and delete outliers. Then, replace missing points with linearly interpolated values. Finally, a clean SCB sequence is achieved. Based on the use of measured Beidou-2 SCB data，the test results show that the quality control strategy of clock bias can significantly improve the accuracy of real information extracted from Beidou-2 SCB and prediction.
