Gravity Recovery and Climate Experiment（GRACE） observations have been used to de-tect the co-seismic and post-seismic gravity field variations due to the Mw=9.3 Sumatra-Andaman earthquake that occurred on December 2...Gravity Recovery and Climate Experiment（GRACE） observations have been used to de-tect the co-seismic and post-seismic gravity field variations due to the Mw=9.3 Sumatra-Andaman earthquake that occurred on December 26,2004.This article focuses on investigating some gravita-tional effects caused by this huge earthquake.We computed the geoid height changes,the equivalent water height（EWH） changes,and the gravity changes using the GRACE Level-2 monthly spherical harmonic（SH） solutions released by University of Texas Center for Space Research（UTCSR）.The GRACE results agree well with the prediction by a dislocation model and are consistent with the results obtained by some previous scholars.In particular,we calculated the three components of the gravity gradient variations and found that they can recover the seismic-related signature more sensitively due to a certain degree of amplification of the signals.A positive-negative-positive mode predominates in the spatial distribution of the horizontal components of the gravity gradient variations,which is possibly attributed to the anomalies in the crustal density distribution caused by the uplift-subduction effect of the dip-slip earthquake.Moreover,the latitude components of the gravity gradient changes show strong suppression of the north-south stripes,which is due to the along-orbit measurements of the two GRACE satellites.We conclude that the posi-tive-negative-positive mode in latitude gravity gradient changes would be a more sensitive fea-ture to detect the deformations of some major dip-slip earthquakes by GRACE data.展开更多
Large earthquakes cause observable changes in the Earth’s gravity field,which have been detected by the Gravity Recovery and Climate Experiment(GRACE).Since most previous studies focus on the detection of near-field ...Large earthquakes cause observable changes in the Earth’s gravity field,which have been detected by the Gravity Recovery and Climate Experiment(GRACE).Since most previous studies focus on the detection of near-field gravity effects,this study provides the results from the medium-to far-field gravity changes caused by the 2004 Sumatra-Andaman earthquake that are recorded within GRACE monthly solutions.Utilizing a spherical-earth dislocation model we documented that large-scale signals predominate in the global field of the coseismic gravity changes caused by the earthquake.After removing the near-field effects,the coseismic gravity changes show a negative anomaly feature with an average magnitude of-0.18×10-8 m·s-2 in the region ranging~40°from the epicenter,which is considered as the'medium ffield'in this study.From the GRACE data released by Center for Space Research from August 2002 to December 2008,we retrieved the large-scale gravity changes smoothed with 3000 km Gaussian ffilter.The results show that the coseismic gravity changes detected by GRACE in the medium field have an average of(-0.20±0.06)×10-8 m·s-2,which agrees with the model prediction.The detection confirms that GRACE is sensitive to large-scale medium-field coseismic gravitational effects of mega earthquakes,and also validates the spherical-earth dislocation model in the medium field from the perspective of satellite gravimetry.展开更多
The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation...The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation and ellipticity. In this study, according to the splitting pattern of Slichter mode, an attempt has been made to detect the possibility of Slichter triplet’s existence by using the product spectra of the long-term continuous gravity measurements from the superconducting gravimeters (SG) at 6 glob- ally-distributed permanent stations in the Global Geodynamics Projects network. The results indicate that the background noise level of the global SG observations is 0.0158 nm s–2 and the magnitude threshold of any global harmonic signals, which may be detected by the global SG, is 0.0152 nm s–2 in the subtidal frequency band from 0.162 to 0.285 cph in which Slichter triplet may occur. it implies that the signatures, related to the triplet, may be identified in the global SG observations, if they exist. It is found that there is a group of global harmonic signatures with the periods of 5.310, 4.995 and 4.344 h emerging significantly from the background noise in the global SG observations. They are in good agreement with the splitting pattern of Slichter mode. It implies that this group of signatures may be related to the inner core translational oscillations. The associated density contrast across the inner core boundary may be deduced as between the values provided in the Earth models of the PREM and 1066 A.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 40974015,40637034)the Fund of Key Laboratory of Geodynamic Geodesy, Chinese Academy of Sciences (No. 09-18)the Fund of Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,China (No. 07-12)
文摘Gravity Recovery and Climate Experiment（GRACE） observations have been used to de-tect the co-seismic and post-seismic gravity field variations due to the Mw=9.3 Sumatra-Andaman earthquake that occurred on December 26,2004.This article focuses on investigating some gravita-tional effects caused by this huge earthquake.We computed the geoid height changes,the equivalent water height（EWH） changes,and the gravity changes using the GRACE Level-2 monthly spherical harmonic（SH） solutions released by University of Texas Center for Space Research（UTCSR）.The GRACE results agree well with the prediction by a dislocation model and are consistent with the results obtained by some previous scholars.In particular,we calculated the three components of the gravity gradient variations and found that they can recover the seismic-related signature more sensitively due to a certain degree of amplification of the signals.A positive-negative-positive mode predominates in the spatial distribution of the horizontal components of the gravity gradient variations,which is possibly attributed to the anomalies in the crustal density distribution caused by the uplift-subduction effect of the dip-slip earthquake.Moreover,the latitude components of the gravity gradient changes show strong suppression of the north-south stripes,which is due to the along-orbit measurements of the two GRACE satellites.We conclude that the posi-tive-negative-positive mode in latitude gravity gradient changes would be a more sensitive fea-ture to detect the deformations of some major dip-slip earthquakes by GRACE data.
基金funded in parts by the Natural Science Foundation of China(grant Nos.40974015,41128003,41174011 and41021061)the Open Fund of Key Laboratory of Geo-dynamic Geodesy of Chinese Academy(No.09-18)the Open Fund of Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,China(No.07-12)
文摘Large earthquakes cause observable changes in the Earth’s gravity field,which have been detected by the Gravity Recovery and Climate Experiment(GRACE).Since most previous studies focus on the detection of near-field gravity effects,this study provides the results from the medium-to far-field gravity changes caused by the 2004 Sumatra-Andaman earthquake that are recorded within GRACE monthly solutions.Utilizing a spherical-earth dislocation model we documented that large-scale signals predominate in the global field of the coseismic gravity changes caused by the earthquake.After removing the near-field effects,the coseismic gravity changes show a negative anomaly feature with an average magnitude of-0.18×10-8 m·s-2 in the region ranging~40°from the epicenter,which is considered as the'medium ffield'in this study.From the GRACE data released by Center for Space Research from August 2002 to December 2008,we retrieved the large-scale gravity changes smoothed with 3000 km Gaussian ffilter.The results show that the coseismic gravity changes detected by GRACE in the medium field have an average of(-0.20±0.06)×10-8 m·s-2,which agrees with the model prediction.The detection confirms that GRACE is sensitive to large-scale medium-field coseismic gravitational effects of mega earthquakes,and also validates the spherical-earth dislocation model in the medium field from the perspective of satellite gravimetry.
基金supported by the National Natural Science Founda-tion of China (Grant Nos. 40574034 and 40730316)Key Project of the Knowledge Innovation of Chinese Academy of Sciences (Grant No. KZCX2 -YW-133)
文摘The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation and ellipticity. In this study, according to the splitting pattern of Slichter mode, an attempt has been made to detect the possibility of Slichter triplet’s existence by using the product spectra of the long-term continuous gravity measurements from the superconducting gravimeters (SG) at 6 glob- ally-distributed permanent stations in the Global Geodynamics Projects network. The results indicate that the background noise level of the global SG observations is 0.0158 nm s–2 and the magnitude threshold of any global harmonic signals, which may be detected by the global SG, is 0.0152 nm s–2 in the subtidal frequency band from 0.162 to 0.285 cph in which Slichter triplet may occur. it implies that the signatures, related to the triplet, may be identified in the global SG observations, if they exist. It is found that there is a group of global harmonic signatures with the periods of 5.310, 4.995 and 4.344 h emerging significantly from the background noise in the global SG observations. They are in good agreement with the splitting pattern of Slichter mode. It implies that this group of signatures may be related to the inner core translational oscillations. The associated density contrast across the inner core boundary may be deduced as between the values provided in the Earth models of the PREM and 1066 A.
