This paper gives a review of fault movement based on geodetic observations. The important role of geodetic observations is discussed in analyzing fault movement in different earthquake cycle phases. First, the evolution of fault movement models is reviewed, including the elastic rebound theory and application of dislocation theory in describing coseismic, interseismic, and postseismic deformation patterns. Then, estimating faults in different earthquake cycle phases is summarized. This study provides support in evaluating seismic risk of a certain fault.
A MS6.4 earthquake occurred at Menyuan, Qinghai province, on January 21, 2016. In 1986, a MS6.4 earthquake happened in the same area with the same focal mechanism. This paper analyzes the regional crustal deformation by using data from the 10 continuous GPS stations and 74 campaign GPS stations in a 200 km range of these events. (1)Based on the velocity field of over ten year’s GPS data, the results of crustal strain rates and seismic moment accumulation rates of the Qilian-Haiyuan fault are significantly higher than other regions. In a 20 km×20 km range of the seismogenic area, the maximum and minimum principal strain rates are 21.5 nanostrain/a (in NW-SE direction, tension) and -46.6 nanostrain/a (in NE-SW direction, extrusion), the seismic moment accumulation rate is 17.4 N·m/a. The principal strain extrusion direction is consistent with the focal mechanism. (2) Based on the GPS continuous stations coordinate time series of 6 years before the event, the result shows the surface expansion at the seismogenic zone is in constant “non-linear” reduced trend since 2010. This means the seismogenic zone is in a state of shrinking. However, 2~3 months before the event, the surface expansion and maximum shear strain occurred with significant inverse trends. These abnormal changes of crustal deformation may reflect the nonlinear adjustment of the stress-strain accumulation when it is close to the critical seismogenic zone.
This paper first presents a BDS/GPS damped LAMBDA algorithm, then introduces a real-time remote deformation monitoring system based on this algorithm. We take the slope deformation monitoring system of Lixian slope for example: BDS has more visible satellites and more stable PDOP values than GPS. Besides, the relative positioning precision of BDS are 0.40 cm, 0.31 cm, 1.00 cm in north, east and up respectively, which are also better than the results of GPS. Long-term related analysis indicates that BDS is superior to GPS in slope deformation monitoring in southern China. During 23 months, the average displacements of the three stations in Lixian slope reach 8.70 cm, 4363 cm, 18.03 cm in north, east and up respectively. As rainfall is a main factor for landslide in soil slope, we build a linear regression model using cumulative rainfall data and cumulative displacement data of which correlation coefficient is above 0.98. Accordingly, one should regard the real-time displacement data and rainfall data as important evidence in landslide early-warning.
Interferometric point target analysis (IPTA) eliminates the effects of atmospheric delay to a certain extent in the monitoring of regional surface deformation, so this paper adopts the idea of neighborhood differencing to reduce the auto-correlated phases in the differential interferograms. Delaunay triangulation with distance constraint is used to establish the baseline network between PS points, effectively avoiding long distance baseline and low quality PS points, and an adjacent array model is applied for searching and deleting the repeated baselines in order to improve computation efficiency. Simulated data are used to validate the program and then eight TerraSAR-X images from July 2015 to February 2016 are used to monitor deformation along the Datong-Xi’an high speed railway based on the program. The results show high consistency with the existing ground fissures and field investigation data, proving that the PS baseline network is practicable in deformation monitoring of linear engineering.
On January 21, 2016, a strong earthquake with a magnitude of MS6.4 occurred at Menyuan, Qinghai province, China. In almost the same region, another strong earthquake occurred in 1986, with similar magnitude and focal mechanism. Based on comprehensive analysis of regional active faults, focal mechanism solutions, precise locations of aftershocks, as well as GPS crustal deformation, we infer that the Lenglongling active fault dips NE rather than SW as was suggested by previous studies. Considering the facts that the 2016 and 1986 MS6.4 Menyuan earthquakes are closely located with similar focal mechanisms, that both quakes are on the north side of the Lenglongling fault and adjacent to the fault, and that the fault is dipping in a NE direction, we suggest that the fault is the seismogenic structure of the two events. The Lenglongling fault, as the western segment of the well-known Tianzhu seismic gap in the Qilian-Haiyuan active fault system, is in a relatively active state with frequent earthquakes in recent years, implying a high level of strain accumulation and a high potential for a future major event. It is also possible that the Lenglongling fault and the adjacent Jinqianghe fault in the Tianzhu seismic gap, will rupture simultaneously in the future.
We select three artificial ground motion time histories in different intensities as in bedrock ground motion inputs. By using the equivalent linearization wave method on the one-dimensional soil frequency domain, we analyze the seismic response of soil layers. The paper studies 2 kinds of soil profile. Their natural density impacts the ground motion parameters. We also analyze characters of peak acceleration and response spectrum. These studies show a negative correlation between surface peak acceleration and soil’s natural density, and that the soil’s natural density increases as the peak acceleration decreases. The correlation between characteristic periods of surface acceleration response spectrum and soil density is ambiguous.
Based on the earthquake catalogues of the Liaocheng-Lankao fault zone and the 50 km surrounding areas since 1970, combined with historical earthquake and seismic background data, we calculate the b-values and point out the highest stress accumulation areas. We use the maximum likelihood and the least square methods, then utilize probability of seismic potential method on north and south segments to calculate the time-dependent seismic potential probability and the background seismicity. We make following conclusions: (1) Fanxian, Qingfeng, Puyang and Juancheng are in high stress accumulation areas, with stable b-values ranging 0.6~0.7.(2) Depending on the time-dependent seismic potential probability, the south of Liaocheng-Lankao fault zone will be more dangerous in the next 50 years and all fault zones will have higher probability of M5.0~6.0 earthquakes occurringin 100 years. (3) The earthquakes in the study areas are mainly concentrated in 115.2°to 115.6°E, 34.9°to 36°N, and the seismicity made greater change more since 2000.
According to seismic wave data recorded by the regional digital seismic network of Ningxia regions, we get the Fourier spectrum with use of the Fourier transform, after speed records of stations geometrical diffusion correction, dielectric attenuation correction, and instrument correction using the Brune model. The Fourier spectrum is integrated to obtain the source displacement spectra in the frequency field, then the corner frequency and zero frequency. Using the radius of the epicenter, the earthquake moments and other small local earthquake source parameters are acquired using genetic algorithms. Finally, we systematically analyze the characteristics of source parameters and the relationship between the various parameters. The paper researches 210 earthquakes of Ningxia regions with ML2.0~4.9, occurring between 2008 and 2014. The results are as follows: the range of seismic moment is 1011~1015 N·m, the range of source radius is 60~766 m, the corner frequency is 1.6~222 Hz, seismic stress drop is in the range of 0.01~7.63 MPa, and apparent stress is in the range of 0.01~3.11 MPa. Some log-linear or semi-logarithmic linear relationships are shown between seismic moment, corner frequency, Richter magnitude, moment magnitude, and other source parameters.
A Xiaozhai landslide numerical model is established by Geostudio software, which is then used to study the stability and seepage characteristics of a landslide at different rainfall conditions and stages. The results show that: the destabilization process of this landslide can be divided into three stages.In the first, Qel + dl4 accumulates;in the second, contact zone (stratum between mudstone and quaternary eluvium) weathers through meeting with water;in the last, the weathered zone is softened and thickened under the humid environment. The formation and development of the softened weathered zone is closely related to highly permeable slide mass and low-permeability slip-bed that is the determining factor of a landslide; The reason a landslide is triggered can be ascribed to low permeability of mudstone, which prevents rainwater infiltration and promotes rainwater enrichment in contact zone. As the rainwater enriches, the weathering of mudstone accelerates and forms a highly weathered weak bed layer. After a severe rainstorm, the weak zone will creep and a landslide happen.
We use geomagnetic omnidirectional intensity profile data across the east Dabie orogenic belt as a foundation. After a series of processing steps, including diurnal reduction, standard reduction to pole, and extraction of the local anomalous field from regional field, we obtain the regional anomalous field. Based on the regional anomalous field, we use the approximate linear inversion method to calculate the average buried depth of Curie interface along the profile, which is 24 km with a maximum 6 km fluctuation. It is found that the depth of the hypocenter in the last 30 years presents dominance distribution between 1 km and 30 km in the study area and its vicinity. The foregoing data shows that the ‘earthquake layer’ coheres well with the ‘magnetic layer’. Combining geologic background with geotectonic evolution, we obtain the seismic precursor relationship with geomagnetic structural features.
Based on the introduction of the TCAR (three carrier ambiguity resolution) model, we analyze factors affecting the TCAR algorithm in the long baseline ambiguity resolution. The TCAR algorithm cannot get the correct ambiguity resolution, so a new method based on triple-frequency geometry-free ionosphere-free combinations is advanced to resolve the long baseline quick ambiguity. Finally, Beidou data are used to validate the new algorithm, showing that the TCAR algorithm can resolvethe short baseline ambiguity, and that the new method can resolve long baseline quick ambiguity.
The regional model of zenith tropospheric delay and precipitable water vapor can help to solve the problem of calculating precipitable water vapor when pressure and temperature data are not available. In this paper, we carry out the correlation analysis of zenith tropospheric delay and precipitable water vapor by the Taiwan Taoyuan (TWTF) station meteorological and zenith tropospheric delay data. Results show there is a significant positive correlation between the two.Further, the seasonal and annual transformation models are established using regression analysis, and seasonal precipitation and non-precipitation data are used to verify the conversion model. The RMS value of GNSS-PWV and linear regression-PWV is less than 1.5 mm, and the maximum error is not more than 3.3 mm. This model is proven to meet the basic requirements of GNSS meteorology.
The prevention of rainstorm disaster is very significant to the security of social economy, ecological environment and human life. Based on the PWV obtained from the Hunan ground-based CORS network (72 stations), along with the atmospheric thermodynamic conditions (temperature and pressure), this study analyzes the time series and plane dynamic variation of PWV before and after a rainstorm occurring April 3-4, 2015, in northern Hunan province. Some regular patterns of change characteristics of water vapor field are summarized. The results show that higher PWV values, which indicate a high probability of a storm, is a necessary condition for rain. Second, when PWV has reached 48 mm, it will be very likely to rain within an hour after the PWV begins to descend. Third, the intensity and duration of precipitation is determined by the peak value (50 mm) and dropping rate (increment) of PWV. Fourth, the variation range of PWV and the atmospheric thermodynamic conditions will determine the hourly precipitation density to a large degree. Lastly, the plane dynamic variation of PWV can accurately predict the actual falling zone of future precipitation.
The global pressure and temperature model (GPT) is an empirical model providing pressure and temperature at any site in the vicinity of the earth’s surface. Aiming at mitigating the shortages of GPT, the GPT2w model is presented, which provides more meteorological data, with a higher horizontal resolution of 5° (GPT2w_5 model) and 1° (GPT2w_1 model). In order to test the accuracy of pressure and temperature of GPT, GPT2w_5 and GPT2w_1 model, the performance of the three models are compared and analyzed at selected sites, based on 1 year (2015.3 to 2016.2) high-precision sounding data from 29 sounding sites in China. The results show that all three models have obvious seasonality and sensitivity to latitude change; the GPT2w_1 model performs as well as the GPT2w_5 model and significantly better than the GPT model; but compared with the GPT2w_5 model, the GPT2w_1 model is more robust.
In this paper, we analyze both the impact of solar radiation during doy 173 to 175 of 2015 on the global ionosphere and the magnetic field, and the influence of higher-order ionosphere on observation and static precise point positioning during a geomagnetic storm. Numerical experimental results show that, affected by the coronal mass ejection in doy 173, the magnetic field is disturbed by a large geomagnetic storm. The maximal second-order ionospheric correction of L1 and L2 is 20 mm and 40 mm. The maximal third-order ionospheric correction of L1 and L2 is 2 mm and 5 mm. Furthermore, the influence of HOI on PPP is mainly visible in the northern direction, showing a southward migration trend, where the maximal influence value is up to 7.1 mm. But the maximal influence value in the direction of U, E is up to 4.6 mm, and is disordered.
Ionospheric grid provides information about space weather, gives empirical forecast models, and helps improve accuracy of user navigation and positioning. Taking into account the wide application of ionospheric grid, based on measured data of some IGS stations, this paper assesses the inner accuracy of ionospheric grid products at five centers and two integrated analysis centers (IGS and iGMAS) worldwide.The results show that there are different accuracy of different types of GIM products in different organizations and different ranges.
In the paper, the adjustment model of the additional systematic parameters of the scale parameter in the current level measurement is reconstructed with the partial errors-in-variables (Partial EIV) model of additional systematic parameters on the scale parameters. The calculation formula and iterative algorithm are given under the criterion of total least squares. Through practical examples and simulation data analysis, the results show that this method and the traditional method have the almost the same effect. Relevant theoretical basis is given.
A circle can be defined as the intersection of a sphere and a plane, where the plane is determined by three arbitrary points. Then the line passes through the center of the circle and the sphere is perpendicular to the circle’s plane. In this paper, we propose a spherical target extraction approach based on these spherical geometry relations. Our algorithm extracts several intersection circles from the point cloud under the predefined constraints, then the center and radius of the spherical target can be determined by minimizing the sum of the distances from the sphere center to the normal vectors of the circles. Experimental comparison with other approaches based on least squares, total least squares and weighted least squares, shows that our spherical target extraction approach is able to achieve higher accuracy and robustness.
We use the empirical orthogonal function (EOF) analysis method to analyze the Kangding MS6.3 earthquake, the main mode and study period between the MS5.0 earthquake above the epicenter, and we discuss the physical meaning of the main mode. The results show that in the normal distribution fitting, there is agreater than 95% probability of accidental error of gravity observation data that is greater than 200 μGal of 7 phases of the Sichuan-Yunnan region. EOF analysis of the second model specification vector and the cumulative gravity changes have similar characteristics. The 6 earthquakes ＞MS6.0 during 2013 to 2014 and the second model specifications vector positive and negative conversion regions have more than 83.3% corresponding rate. This shows a long-term variation pattern in the gravity field. The first mode before and after the earthquake specification series is the coseismic signal, spatial similarity of 4 quadrant distribution and 4 earthquakes MS＞6.0 in 2014 and the second mode vector specification of positive and negative conversion area of 100% corresponding rate, which indicates that the model of the region can represent short-term variations of the gravity model. EOF analysis method is used to study the temporal and spatial variations of the first mode and the normal vector of the Ganzi-Shimian section of the Kangding river before and after the Kangding MS6.3 earthquake. The results show that the distribution of the 4 quadrants of the specification values has already appeared in the latter half of the year. All the first mode results before the Kangding MS6.3 earthquake are included in this feature. According to the characteristics of the constant increase of the epicenter location, the change is from negative to positive before and after Kangding earthquake.
We use the Changshu seismic station water tube meter and vertical tilt data from the 2009~2015 observed pendulum, in relation to changes in the natural environment (air pressure, rainfall, temperature, temperature of the cave, etc.). The characteristics of these influences are analyzed, and the results show that: (1) rainfall interference on observation data is most significant for the NS component with south dipping and the EW component occurs with west dipping; the magnitude of the NS component interference is larger than that of the EW component; and the vertical pendulum interference is greater than that of water tube tiltmeter. (2) Pressure changes affect short cycle micro dynamic interference which leads to the daily value curve short time distortion. (3) The variation of the temperature and the temperature of the tunnel caused by the change of the observed value is obvious, but the effect of the observation value is not obvious.
According to the characteristic of the GB-SAR affected by many factors and complex relationship in the open pit mine slope ground disaster monitoring, it used genetic algorithm optimized BP neural network model to analyze the monitoring effectiveness of the GB-SAR. The neural network takes the scan gradient, scan slope direction and the radar echo intensity as the input, takes the obtained points number of deformation monitoring as the output, and uses the Pearson correlation coefficient method to analyze the relevant properties and related degree of the influence factors. The results show that the GA-BP algorithm is suitable for monitoring effectiveness analysis of GB-SAR, and it is effective and superior.
