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Detection of spheriodal free oscillation excited by Peru 8.2 M_(s) earthquake with five international superconducting gravimeter data

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Science China Earth Sciences 2005年第1期48卷 123-133页

作者： LEI Xiang'e XU Houze SUN Heping key laboratory of dynamic geodesy Institute of Geodesy and Geophysics. Chinese Academy of Sciences Wuhan 430077 China Key Laboratory of Dynamic Geodesy Institute of Geodesy and Geophysics. Chinese Academy of Sciences Wuhan 430077 China Key Laboratory of Dynamic Geodesy Institute of Geodesy and Geophysics. Chinese Academy of Sciences Wuhan 430077 China

In this paper, authors obtain the spectral peaks of the earth free oscillation and check all normal modes from 0S0 to 0S48 accurately, with the Fourier analysis and the maximum entropy spectrum method dealing jointly with six groups of the observational residual data from five international superconducting gravimeter stations. By comparing the observational results in this paper with three former groups of observations or models, authors notice an extra discrepancy between two observational 0S2 modes excited separately by Peru earthquake and Alaska earthquake, which probably mirrors the anisotropy of the Earth's inner core. The analysis on the splitting 1S2 mode shows that the asymmetric factor of rotationwise spectral splitting is possible to be different from that of anti-rotationwise spectral splitting.

关键词： 8.2 Ms Peru earthquake, detection of Earth free oscillation, observation of superconducting gravimeter,anisotropy of earth's inner core.

Focal Mechanism and Rupture Process of the 2012 M_w 7.0 Santa Isabel, Mexico Earthquake Inverted by Teleseismic Data

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Journal of Earth Science 2015年第3期26卷 384-390页

作者： Chengli Liu Yong Zheng Xiong Xiong State key laboratory of geodesy and Earth's dynamic Institute of Geodesy and Geophysics Chinese Academy of Sciences

The point source parameters of the April 12, 2012 Mw 7.0 Santa Isabel, Mexico, earthquake indicated by teleseismic P and SH waveforms obtained by a means of traditional cut and paste（CAP） method show that the best double-couple solution of this event is： 37°/127°, 90°/81° and-9°/-180° for strike, dip and rake, respectively. Its centroid depth is 13 km. Global teleseismic waveform data exhibit that the rupture of the earthquake initiated at a focal depth of 13 km and propagated southeastward with a relatively slow rupture velocity（about 1.8 km/s on average）. The maximum slip occurred at 30 km southeast of the hypocenter, with the peak slip of 3.57 m and total seismic moment of whole fault up to 3.98×1019 N·m. These observations provide some insight into properties, co- or post-seismic deformation and coulomb stress changes of future earthquake in this area.

关键词： Mexico Earthquake rupture velocity focal mechanism slip history

Check of Earth's free oscillations excited by Sumatra-Andaman Large Earthquake and discussions on the anisotropy of inner core

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Science China Earth Sciences 2007年第6期50卷 909-917页

作者： HSU HouTse key laboratory of dynamic geodesy Institute of Geodesy and GeophysicsChinese Academy of SciencesWuhan 430077China

Sumatra-Andaman Large Earthquake on Dec. 26,2004 generated not only the Indian Ocean Tsunami but also the Earth's free oscillations (EFO). The signals of Earth's free oscillations were perfectly re-corded by the superconducting gravimeter C0-32 at Wuhan station in China. After the pre-treatment and spectral analysis on the observational data from Wuhan station,we obtained more than ninety EFO modes including 42 fundamental modes,2 radial modes and 49 harmonic modes. On the basis of the discussions on some observed harmonic modes and abnormal splitting phenomena,we considered that the real rigidity might be lower than the theoretical prediction of PREM model in the inner core and however the anisotropy of compressive wave was brightly higher than the present estimations in the inner core. This suggested that the anisotropy of the inner core could be much more complicated than our present understanding,and there might be some new geophysical phenomena in the formation process of the inner core.

关键词： Sumatra-Andaman Large Earthquake Earth’s free oscillations superconducting gravimeter abnormal spectral splitting anisotropy of inner core

Study on characteristics of long-term gravity changes at Wuhan station

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Chinese Science Bulletin 2008年第13期53卷 2033-2040页

作者： XU JianQiao ZHOU JiangCun LUO ShaoCong SUN HePing key laboratory of dynamic geodesy Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China

We consider the characteristics of long-term changes in non-tidal gravity and their implication to the local perturbations in barometric pressure and water storage and to the local vertical crustal movement using the long-term continuous gravity observations from a superconducting gravimeter (SG) at Wu-han station,together with the co-site measurements from a Global Positioning System (GPS) receiver and an absolute gravimeter FG5. The observation results indicate that there are obvious seasonal variations in the long-term gravity changes measured with the SG. About 70 percent of the whole sea-sonal changes come from the contribution of the local disturbances in air pressure and water storage,while over 95 percent of the annual changes are attributed to the loading effects of these environmental perturbations. Due to the absence of direct measurements of the local water storage,especially those of the underground water,the global assimilating models of land water LaD (Land dynamics) and GLDAS (Global Land Data Assimilation System) cannot virtually describe the real hydrologic distur-bances around the station. The resulting gravity changes,which are simulated theoretically by means of convolution integration of the loading Green’s functions and water models LaD and GLDAS,show significantly time delay of about 55 days from those measured with the SG. Compared with the meas-urements of the absolute gravity with the FG5,the long-term drift rate of the SG is determined as about 17.13 nms-2/a. From the co-site GPS measurements,it is found that the local crust is slowly subsiding at a rate of 3.71±0.16 mm/a,and the related gravity variation is estimated as 13.88±0.22 nms-2/a. In other words,the ratio of the changes in gravity and altitude related to the local vertical crustal movement is about -37.41 nms-2/cm. It implies that a considerable mass adjustment may be associated with the local vertical crustal movement,and its dynamic mechanism should be investigated further.

关键词：超导重力计潮汐引力气压水储存量

Detection of Inner Core Translational Oscillations Using Superconducting Gravimeters

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Journal of Earth Science 2013年第5期24卷 750-758页

作者：江颖徐建桥孙和平 State key laboratory of geodesy and Earth’s dynamic Institute of Geodesy and GeophysicsChinese Academy of Sciences University of Chinese Academy of Sciences

An attempt has been made to search for the translational oscillations of the Earth＇s solid inner core in the gravity measurements recorded with the superconducting gravimeters （SG） from the worldwide network of the Global Geodynamics Project （GGP）. All the SG data were prepared and analyzed by the same method to remove accurately the signatures related to gravity tides, local baro- metric pressure, the Earth＇s rotation, the long-term trend and so on. We obtained the estimations of the power spectral densities of each residual series and the estimations of the product spectral densities in the subtidal band （0.162-0.285 cph） were obtained by using a multi-station stacking technique after further eliminating atmospheric effects. The inner core translation triplet was detected in the subtidal band. We find 6 groups of signal with high signal-to-noise ratio that are consistent with the characteris- tics of the triplet, and 4 groups of the results that are close to the previous studies and the differences are less than 0.92%. It implies that the groups of signatures all have the possibility to be related to the inner core translational oscillations.

关键词： Slichter mode triplet the product spectral density global superconducting gravimeters.

Forward Simulation of Gravity for Crustal Structure of Xiachayu-Gonghe Profile in Eastern Tibetan Plateau

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Geo-Spatial Information Science 2010年第4期13卷 300-305页

作者： KE Xiaoping WANG Yong XU Houze key laboratory of dynamic geodesy Institute of Geodesy and Geophysics Chinese Academy of Sciences 340 Xudong StreetWuhan 430077 China

The crustal structure of Xiachayu-Gonghe geophysical profile in eastern Tibetan plateau is simulated with Bouguer anomaly corrected for sediments and lithosphere. The forward simulation shows that the thickness of upper crust in eastem Tibetan plateau is about 20 km, and the density is 2.78 × 10^3 kg/m^3. The bottom interface of middle crust changes from 30 km to 40 km, the density of middle crust is 2.89 × 10^3 kg/m^3. The materials with low density of 2.78 × 10^3 kg/m^3 exist in middle crust, and those with high density of 3.33 × 10^3 kg/m^3 exist at the bottom of middle crust between Wenquan and Tanggemu. The density is 3.10× 10^3 kg/m^3 in lower crust. The shallowest depth of Moho interface is about 56 km, and the deepest one is about 74 km, the undulation of interface is large, the deep Moho is located in Xiachayu, Chayu, Nujiang, and Wenquan. The crustal density of eastern Tibetan plateau is larger than that of central section; the low velocity layers are located in middle crust and bottom in eastern Tibetan plateau and at the bottom of the upper crust in the central plateau.

关键词： crustal structure Tibetan plateau gravity forward simulation

Temporal variations in free core nutation period

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Earthquake Science 2009年第4期22卷 331-336页

作者： Jianqiao Xu Heping Sun key laboratory of dynamic geodesy Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China

Based on the nearly diurnal resonance in the tidal gravity observations, the temporal variations in period of the Earth＇s free core nutation （FCN） are investigated by using the tidal gravity observations of 18-year duration recorded continu- ously with a superconducting gravimeter （SG） at Brussels. The effects of the global oceanic tide loading and local barometric pressure on the SG observations have been removed by using eleven high-precision global digital models of oceanic tides and barometric pressure measurements recorded simultaneously at the same site. The results indicate that there exist decade-scale variations in the FCN period. The results should be further confirmed by the measurements using other space-based geodetic techniques （such as the very long baseline interferometry） and the SG observations from globally distributed stations.

关键词： nearly diurnal resonance superconducting gravimeter tidal gravity observations period of the free core nutation temporal variation

Accurate and rapid error estimation on global gravitational field from current GRACE and future GRACE Follow-On missions

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Chinese Physics B 2009年第8期18卷 3597-3604页

作者：郑伟许厚泽钟敏员美娟 key laboratory of dynamic geodesy Institute of Geodesy and GeophysicsChinese Academy of Sciences Disaster Prevention Research Institute Kyoto University Department of Applied Physics Wuhan University of Science and Technology

Firstly, the new combined error model of cumulative geoid height influenced by four error sources, including the inter-satellite range-rate of an interferometric laser （K-band） ranging system, the orbital position and velocity of a global positioning system （GPS） receiver and non-conservative force of an accelerometer, is established from the perspectives of the power spectrum principle in physics using the semi-analytical approach. Secondly, the accuracy of the global gravitational field is accurately and rapidly estimated based on the combined error model; the cumulative geoid height error is 1.985× 10^-1 m at degree 120 based on GRACE Level 1B measured observation errors of the year 2007 published by the US Jet Propulsion laboratory （JPL）, and the cumulative geoid height error is 5.825 × 10^-2 m at degree 360 using GRACE Follow-On orbital altitude 250 km and inter-satellite range 50 km. The matching relationship of accuracy indexes from GRACE Follow-On key payloads is brought forward, and the dependability of the combined error model is validated. Finally, the feasibility of high-accuracy and high-resolution global gravitational field estimation from GRACE Follow-On is demonstrated based on different satellite orbital altitudes.

关键词： global gravitational field GRACE Follow-On semi-analytical approach combined error model

Co-and post-seismic surface deformation and gravity changes of MS 7.0 Lushan,earthquake

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Earthquake Science 2013年第3期26卷 207-212页

作者： Kai Wang Chengli Liu Xiong Xiong Yong Zheng key laboratory of dynamic geodesy Institute of Geodesy and GeophysicsCAS University of Chinese Academy of Sciences

On April 20, 2013, an earthquake with mag- nitude 7.0 occurred in the southwest of the Longmenshan fault system in and around Lushan County, Sichuan Province, China. This devastating earthquake killed hun- dreds of people, injured 10 thousand others, and collapsed countless buildings. In order to analyze the potential risk of this big earthquake, we calculate the co- and post-seismic surface deformation and gravity changes of this event. In this work, a multilayered crustal model is designed, and the elastic dislocation theory is utilized to calculate the co- and post-seismic deformations and gravity changes. During the process, a rupture model obtained by seismic waveform inversion （Liu et al. Sci China Earth Sci 56（7）： 1187-1192, 2013） is applied. The time-dependent relaxation results show that the influences on Lushan and its surrounding areas caused by the Ms7.0 Lushan earthquake will last as long as 10 years. The maximum horizontal displacement, vertical uplift, and settlement are about 5 cm, 21.24 cm, and 0.16 m, respectively; the maximal positive and nega- tive values of gravity changes are 45 and -0.47 μGal, respectively. These results may be applied to evaluate the long-term potential risk caused by this earthquake and to provide necessary information for post-earthquake reconstruction.

关键词： Lushan earthquake Viscoelasticrelaxation Surface deformation Gravity