Chinese Journal of Geophysics最新文献

Because the sensitivity of the disturbing intersatellite range measurements to the recovery accuracy of the Earth's gravitational field is superior to that of the intersatellite range measurements, the observation equation of a new Disturbing Intersatellite Range Method (DIRM) is created in this study. Then the orbital stability of the next-generation Hybrid-Inline-Pendulum-Three-Satellite (HIP-3S) formation is efficiently verified. The research results indicate that the HIP-3S formation is sufficiently steady for further enhancing the accuracy of the future Earth gravity field model. Finally, the Earth's gravitational field complete up to degree and order 120 is precisely recovered by the current GRACE-2S inline formation and the next-generation HIP-3S combined formation based on the new DIRM, and the cumulative geoid height errors are 2.271×10⁻¹ m and 1.923×10⁻³ m at degree 120, respectively. The study results show that the future HIP-3S formation is helpful for producing the next-generation Earth gravity field model with higher accuracy and spatial resolution.

Based on existing three-dimensional (3-D) thunderstorm electrification and discharge model, this work coupled with a classical parameterization scheme of aerosol activation is used to simulate a case of tropical convection in Changchun. The study shows that the change of aerosol concentration has an important influence on the microphysics, electrification and discharge processes of thunderstorm clouds. The results show that: (1) As the aerosol concentration increases in the polluted thunderclouds, the increase of the number of cloud droplets and the updraft cause the increase of the number of ice crystal and graupel, but the decrease of the scale; (2) Compared to the clean thunderclouds, the non-induced electrification process is weak, while the induction electrification process is strong, and the duration of electrification become longer in polluted thunderclouds; (3) The first charge time of the polluted thunderclouds delays, but the total lightning frequency increases and duration is longer. Meanwhile, the frequency of the cloud-to-ground flash in the polluted thunderclouds increases, and the increase of the positive cloud-to-ground flash is more obvious.

As having experienced multi-stage tectonic magmatic activity, the structure of the lithosphere in the east part of South China is very complicated and the distribution of magma has obvious regularity. In order to study the deep tectonic background of magmatic activity of the different blocks in the east part of South China, this paper made a series of qualitative and quantitative analysis based on the Ji'an-Fuzhou magnetotelluric sounding profile data crossing the east part of South China. The subsurface dimensionality was analyzed by the Bahr phase decomposition, the geoelectric strike with different frequencies was obtained by the single-site multifrequency Groom-Bailey decomposition. Finally, the non-linear conjugate gradients (NLCG) was used to calculate the 2D resistivity structure in our research area.

The electrical structure model shows that there are significant differences between the two blocks-Wuyi uplift belt and Southeast coastal fold belt. It can be vertically divided into four electrical layers of the high resistivity layer in upper crust, the low resistivity layer in mid-lower crust, the sub-high resistivity layer in the lithosphere mantle, the low resistivity in the asthenosphere. In the upper crust, the high resistivity layer of more than 10000 Ωm indicates the distribution of granite whose bottom interface is about 15∼20 km deep. In the mid-lower crust, the high-conductivity layer in the Wuyi uplift belt is thin and of small scale. It is associated with the thrust faults. However, in the Southeast coastal fold belt, the high-conductivity layer is thicker and of larger scale. It is uplifted in a mushroom-shape. The resistivity in lithosphere mantle gradually reduces from inland to coast. Due to the limited detecting depth, the lithosphere-asthenosphere boundary (LAB) doesn't show in the Wuyi uplift belt which indicates the depth of the LAB is more than 100 km. In the Southeast coastal fold belt, the thickness of the lithosphere is reduced to 60 km, and the asthenosphere has an uplift tendency.

In the east part of South China, there are a series of discontinuous high-conductivity layers of different scales in the crust. The scale and burial depth of the high-conductivity layers are closely related to the deep tectonic environment and fault distribution. Combining with gravity and magnetic results, we discussed the formation mechanism of high-conductivity layer. It is inferred that the high-conductivity layer in the crust of the Southeast coastal fold belt is the result of partial melting by asthenosphere upwelling and basaltic magma underplating. While the high-conductivity layer in the Wuyi uplift belt is the result of incomplete condensation of the magma chamber after crust material remelting in the early compression environment, and the continuous heating from the deep heat flow in an extensional environment.

The lithosphere structure in the east part of South China has a marked zoning, and the high-condu

Near-field seismic localization has important significance and wide applications in the real world, for instance, locating explosions or tracking traffic movements. The traditional methods designed for far-field scenarios are limited here due to the unknown velocity structures and high accuracy demands. This paper, for the first time, applied the Delta T Mapping (DTM) technique from acoustic emission detection in near-field seismic localization. DTM first needs to construct a mapping of the difference of first arrivals on which the following locating is based. There are two approaches for establishing such model: (1) grid search method: using linear scattered point interpolation to obtain new DTM of higher resolution; (2) statistical locating method: using Gaussian Process Regression to build the mapping from Delta T to positions. The experiment was conducted in an area of 140 m×90 m in the suburb of Beijing. The locating error was 0.5∼5.1 m. The results showed that DTM is reliable, highly accurate and suitable for real-time use for near-field seismic localization. The cost of learning DTM and analyzing data could be further decreased while obtaining highly accurate DTM by switching the sources and receivers. Furthermore, combining source-scan algorithm has certain potential to locate multi-sources.

Due to the high density of observation points and shots, we obtained the 21-shot seismic data with high signal-to-noise ratio along the 1334 km long Dafeng-Baotou profile. On the basis of the analysis of the Pg wave phase characteristics, we processed the data by the inversion method and constructed the fine structure of the basement, revealing the discrepancy of basement structure in different tectonic blocks. The basement depth of Northern Jiangsu basin is 4.5∼9.0 km and that of Jiangsu-Shandong uplift is 1.5∼2.0 km. Strong fluctuations of the burial depth and velocity structure may be considered as the seismologic manifestation of the collision and extrusion between North China and the Yangtze plate. The basement of Western Shandong uplift area shows the feature of shallow burial depth, high speed and stable structure, while the Pg wave characteristics in the North China basin are lagged travel time, low apparent velocity, basement depth from 7.0 km to 10.0 km, and the local fluctuations in the velocity structure and basement interface. Lots of phenomena above reveal that this area is a large-scale basement depression zone with thick Cenozoic sediment. Moreover, in different tectonic units of the basin, the tectonic pattern of local basement patch and coexistence of depression and uplift shows obvious tectonic characteristics, such as remarkable Cenozoic sedimentary activities, significant velocity and thickness changes and the unstable structure. Taihang mountain piedmont fault and Liaolan fault are significant seismologic features. On both sides of these two faults, the velocity structure shows intensive lateral heterogeneity, and the basement interfaces collapse as cliff. This study reveals that the Taihang mountain piedmont fault is an important tectonic zone in North China. Its complexity is not only reflected in different landforms and strata on its two sides, but also reflected in the significant differences among the basement depth, velocity structure, the crust and even the mantle lithospheric structures. To the east of Taihang mountain, the important symbol is large scale crustal and lithospheric thinning, which result in the obvious differences and strong lateral heterogeneity of the basement structure, the crust and even the lithosphere structures between the western and eastern North China Craton destruction

With high accuracy and stability of GPS radio occultation (RO) data in the stratosphere, COSMIC data is used to validate the Microwave Temperature Sounder (MWTS) channel 4 (ch4) measurements on serial FY-3 satellite platforms. A 2-year comparison between the simulated and observed T_b for MWTS ch4 shows that both MWTS observed T_b on FY-3A/3B in lower stratosphere are overestimated, especially in the tropics and summer of high-latitude region. The trends of T_b bias are more consistent on both FY-3A/3B satellites in the two years. The variations of T_b bias for MWTS ch4 in four latitude-zones are quite different: the T_b bias is obviously positive about 2∼4 K in the tropics, and is stably positive about 1 K in the mid-latitude, while the T_b bias is evidently varied with seasons from negative in winter to positive in summer in high-latitude, particular in southern high-latitude the difference of T_b bias among seasons is about 5 K, such strong dependence on environment temperature for T_b bias is not mainly caused by the shifted central frequency. In the tropics the difference of the observed and simulated T_b is more significant, and the influence of matching samples in the tropics on the global T_b bias is more than 20%, which implies that it should be cautious to use the validating results derived from COSMIC in the tropics.

Crustal lithology transformation, lithological variations with depth and tectonic deformation in the Tibetan plateau are the key to explore the crustal thickening and material motion in this region. Located in the central plateau, the Bayan Har block has a vast geographical territory. To make a further study on the fine crustal structure in the central and eastern Bayan Har block, we conduct a comprehensive analysis of the deep seismic wide-angle reflection/refraction phase data of different areas of this block, and then perform detailed simulation calculation of the travel-time and amplitude characteristics of different phases using the synthetic reflectivity seismograms. The results indicate that the thickness of the Bayan Har block varies from 50 km to 60 km, increasing westward gradually. The average velocity in the crystalline crust is 6.07∼6.18 km·s⁻¹, which is obviously reduced, and there are several strong reflection interfaces in the crust, which differ in different regions. In the east, the Zoigě basin has a low velocity within the crust and a clear crust-mantle boundary. In the central part, a high velocity structure (6.8 km·s⁻¹) is present beneath the Yushu-Madoi segment with an unclear crust-mantle boundary, i.e. the Moho interface transformed into a high velocity gradient layer with a thickness of 2∼4 km. These characteristics indicate the discrepancy of crustal thickening and lithology transformation within the Bayan Har block. Multi-group strong reflections in the crust and the low apparent velocity indicate the shattered, low-velocity, weakened, creeping, and possibly decoupling structures in the crust. High apparent velocity phase in the lower crust displays that there may be stable original crust residual or material exchanging with the upper mantle under the background of the crustal thickening and transformation in the Tibetan plateau. The diversity of different areas within the Bayan Har block involves the crustal thickening, lithology structure, crystalline basement and crust-mantle boundary nature transformation, which can provide new insights into the understanding of the crustal deformation and dynamical process in the Tibetan plateau.

We calculate the gravity anomalies due to lateral changes in bathymetry from an independent topography compilation, and those due to changes in sediment thickness and density. To obtain the Moho depth and the crustal thickness of the South China Sea basin, the 3-D gravity inversion method is employed, based on an “initial model of fluctuating interface” constrained by the control points from seismic data and sonobuoys. And then, the gravity data is corrected for the lithospheric thermal gravity anomaly within continental margin due to lithosphere thinning. Over most of the South China Sea basin, the Moho depth ranges between 8∼14 km, the crustal thickness is 3∼9 km. The NNE trending fossil spreading center of the East and the Southwest Basin extend to 112°E, the Moho depth is more than 12 km, the crustal thickness is above 6 km in the spreading center. However, the crust of the spreading center at the northwest basin is not obviously thickened. In the northern margin of the southwest basin, south of Zhongsha block, there is a crustal thinning belt, nearly EW trending, where the crustal thickness is about 9∼10 km. The 14 km isoline of the Moho depth and the 9 km isoline of the crustal thickness are very close to the Continent-Ocean Boundary.

On February 6, 2016, an M_w6.4 earthquake struck the Meinong District of Kaohsiung city in Taiwan, China. Various researches have been conducted on the earthquake. Most of these researches are based on seismic data and no consensus has been reached on the fault structure and focal parameters yet. Surface displacement obtained by interferometric synthetic aperture radar (InSAR) is widely used in earthquake studies because of its high resolution and accuracy with large and continuous coverage. Therefore, this study selects InSAR and GPS data to investigate the focal mechanism and slip distribution of the 2016 Meinong earthquake. Using the dual-track differential InSAR (D-InSAR) technology, we extract the coseismic deformation field of this earthquake with SAR data (both the ascending and descending) from satellite ALOS2 and the ascending data from satellite Sentinal-1A. The results show that the maximum deformation occurs in the west of the epicenter, with an uplift around 11.2 cm.

The uniform dislocation model and multiple peak particle swarm optimization (MPSO) algorithm are employed to determine the fault geometry parameters of this earthquake based on the InSAR and GPS data. The results show that the rupture is a reverse fault with sinistral strike-slip with the average slip angle of 51.5°. The seismic source is at 22.920°N, 120.420°E, and a depth of 12 km. The rupture plane is about 15 km long with a strike angle of 307° and a dip angle of 16.5°. The optimal dip angle (15.7°), weighting ratio (18:1) between GPS and InSAR and the smoothing factor (0.06) obtained by the grid iteration method together with the non-uniform model and the non-negative least squares method are used to obtain the detailed slip distribution. The results show that the maximum value of dip slip and strike slip are 51.7 cm and 55.3 cm, respectively. The moment magnitude of the non-uniform model is M_w6.38, slightly smaller than the result of GCMT (M_w6.4). The comparison between our research and previous research and the analysis of the regional faults indicate that a single fault geometry is more reasonable and it can fit both the GPS and InSAR data well. We also find that the ruptured fault is a blind fault located in the area among Zouchen fault and Chishan fault with an ES-WN strike and dipping toward ES. So we believe this fault should have some relation with the 2010 M_w6.3 Jiashian earthquake.

Based on the in situ stress measurement data from “Fundamental Database of Crustal Stress Environment in Continental China”, nearly 2000 pieces of data have been properly picked out, covering the geographic space of 21°N–40°N and 73°N–110°N and the depth of 0∼2 km. By excluding the gravity effect on in-situ stress in the target area, and taking the uneven distribution of the sample data along depth into consideration, the effect of tectonic stress field will be analyzed in this paper. In order to exclude the gravity effect, two modes, namely Heim's hypothesis and A. H. Gennik's hypothesis, have been adopted to estimate the upper and lower limits, under which the tectonic stress characteristic of the shallow crust in Qinghai-Tibet Plateau and its periphery have been studied. As shown in the results: (1) The maximum horizontal stress σ_H and minimum horizontal stress σ_h in Tibetan Plateau and its periphery increase linearly with the depth D: σ_H = 22.115D + 5.761, σ_h = 14.893D + 3.269; and the estimated magnitudes of the maximum horizontal tectonic stress σ_T and minimum horizontal tectonic stress σ_t vary as follows respectively: 4.609 < σ_t < 15.522D + 4.609, 3.121 < σ_t < 6.366D + 3.121(D > 0); tectonic difference stress σ_T – σ_t = 7.222D + 2.492, surface value (D = 0 km) is about 2.5 MPa, and increases at a gradient of 7.2 MPa·km^–1 with the depth. (2) Within the measured depth scale, σ_T, σ_t and σ_T – σ_t values of Qinghai-Tibet block and research areas in the northern/middle/southern segments of North-South seismic belt all increase linearly with the burial depth; when D = 1 km, the maximum of σ_T values from statistical regression of all blocks is 30.1 MPa, and the minimum is 17.6 MPa, with the blocks in descending order of values such as: Qinghai-Tibet block, northern segment, middle segment and southern segment of the North-South seismic belt; when D = 1 km, the maximum of σ_T – σ_t values from statistical regression of all blocks is 15.8 MPa, and the minimum is 8.9 MPa, with the blocks in descending order of values as: Qinghai-Tibet block, northern segment, middle segment and southern segment of the North-South seismic belt. Generally, the stress magnitudes in Qinghai-Tibet block are stronger than those in the North-South seismic belt. (3) Compared with the North-South seismic belt, an obvious feature of “stronger tectonism in the deep crust than that in the shallow” is shown in the crust of Qinghai-Tibet block under northward compression.