{"title":"在印度古吉拉特邦库奇用超导重力仪观测2010年智利和2011年日本地震后的自由振荡","authors":"Chandra Sekhar Pedapudi , Madhusudhana Rao Katlamudi , Severine Rosat","doi":"10.1016/j.geog.2022.10.002","DOIUrl":null,"url":null,"abstract":"<div><p>In this paper, we present observations of free oscillations of the Earth after major earthquakes in Chile (February 27, 2010, <em>M</em><sub>W</sub>8.8) and Japan (March 11, 2011, <em>M</em><sub>W</sub>9.1) using data from the dual-sphere superconducting gravimeter (SG - 055), installed at Badargadh (23°0.47 N, 70°0.62 E), Kutch, Gujarat, India in March 2009. To see the noise characteristics, we calculated the power spectral density of the gravity time series of 5 quiet days in the frequency band 0.05–20 mHz using the new low noise model (NLNM) as a reference. We compared the noise level of the Badargadh site to other SG sites around the world. This shows that the Badargadh SG is in a low noise state. We find that the noise increases at frequencies below 1 mHz. Such a characteristic is also observed in Djougou (Afrique, Benin) and Strasbourg (France). Using theoretical tides for Gujarat, we estimated a scale factor of about −814 nm/s<sup>2</sup>/V for Grav1 (lower-sphere) and about −775 nm/s<sup>2</sup>/V for Grav2 (upper-sphere). We corrected the influence of atmospheric pressure from the one-second gravity data before switching to the frequency domain. We extracted a total of 53 Earth's Free Oscillations (EFO) modes during the earthquake in Japan and about 47 EFO modes during the earthquake in Chile. We are able to extract the lowest <sub>0</sub>S<sub>2</sub> spheroidal mode (0.30945 mHz or 54 min) and <sub>0</sub>S<sub>0</sub> radial mode (0.81439 mHz or 20 min). The longer time series shows individual <sub>0</sub>S<sub>2</sub> singlets and <sub>0</sub>S<sub>3</sub> (0.46855 mHz) singlets due to the Coriolis splitting effect. We cross-referenced the frequencies of these modes using the PREM model and previous global observations. The correlation coefficient between the observed and the PREM model for these two events are 0.999 for Japan earthquake and 0.993 for Chile earthquake. This validates the quality of the data useful for low-frequency studies in seismology. We also calculated the relative deviations of our observed fundamental modes with previously determined observed and theoretical values. We found that the relative deviations of our observed free oscillations do not exceed 0.5%, indicating good correlations.</p></div>","PeriodicalId":46398,"journal":{"name":"Geodesy and Geodynamics","volume":"14 1","pages":"Pages 52-64"},"PeriodicalIF":2.8000,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":"{\"title\":\"Observation of free oscillations after the 2010 Chile and 2011 Japan earthquakes by superconducting gravimeter in Kutch, Gujarat, India\",\"authors\":\"Chandra Sekhar Pedapudi , Madhusudhana Rao Katlamudi , Severine Rosat\",\"doi\":\"10.1016/j.geog.2022.10.002\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>In this paper, we present observations of free oscillations of the Earth after major earthquakes in Chile (February 27, 2010, <em>M</em><sub>W</sub>8.8) and Japan (March 11, 2011, <em>M</em><sub>W</sub>9.1) using data from the dual-sphere superconducting gravimeter (SG - 055), installed at Badargadh (23°0.47 N, 70°0.62 E), Kutch, Gujarat, India in March 2009. To see the noise characteristics, we calculated the power spectral density of the gravity time series of 5 quiet days in the frequency band 0.05–20 mHz using the new low noise model (NLNM) as a reference. We compared the noise level of the Badargadh site to other SG sites around the world. This shows that the Badargadh SG is in a low noise state. We find that the noise increases at frequencies below 1 mHz. Such a characteristic is also observed in Djougou (Afrique, Benin) and Strasbourg (France). Using theoretical tides for Gujarat, we estimated a scale factor of about −814 nm/s<sup>2</sup>/V for Grav1 (lower-sphere) and about −775 nm/s<sup>2</sup>/V for Grav2 (upper-sphere). We corrected the influence of atmospheric pressure from the one-second gravity data before switching to the frequency domain. We extracted a total of 53 Earth's Free Oscillations (EFO) modes during the earthquake in Japan and about 47 EFO modes during the earthquake in Chile. We are able to extract the lowest <sub>0</sub>S<sub>2</sub> spheroidal mode (0.30945 mHz or 54 min) and <sub>0</sub>S<sub>0</sub> radial mode (0.81439 mHz or 20 min). The longer time series shows individual <sub>0</sub>S<sub>2</sub> singlets and <sub>0</sub>S<sub>3</sub> (0.46855 mHz) singlets due to the Coriolis splitting effect. We cross-referenced the frequencies of these modes using the PREM model and previous global observations. The correlation coefficient between the observed and the PREM model for these two events are 0.999 for Japan earthquake and 0.993 for Chile earthquake. This validates the quality of the data useful for low-frequency studies in seismology. We also calculated the relative deviations of our observed fundamental modes with previously determined observed and theoretical values. We found that the relative deviations of our observed free oscillations do not exceed 0.5%, indicating good correlations.</p></div>\",\"PeriodicalId\":46398,\"journal\":{\"name\":\"Geodesy and Geodynamics\",\"volume\":\"14 1\",\"pages\":\"Pages 52-64\"},\"PeriodicalIF\":2.8000,\"publicationDate\":\"2023-01-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"1\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Geodesy and Geodynamics\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S167498472200091X\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Geodesy and Geodynamics","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S167498472200091X","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Observation of free oscillations after the 2010 Chile and 2011 Japan earthquakes by superconducting gravimeter in Kutch, Gujarat, India
In this paper, we present observations of free oscillations of the Earth after major earthquakes in Chile (February 27, 2010, MW8.8) and Japan (March 11, 2011, MW9.1) using data from the dual-sphere superconducting gravimeter (SG - 055), installed at Badargadh (23°0.47 N, 70°0.62 E), Kutch, Gujarat, India in March 2009. To see the noise characteristics, we calculated the power spectral density of the gravity time series of 5 quiet days in the frequency band 0.05–20 mHz using the new low noise model (NLNM) as a reference. We compared the noise level of the Badargadh site to other SG sites around the world. This shows that the Badargadh SG is in a low noise state. We find that the noise increases at frequencies below 1 mHz. Such a characteristic is also observed in Djougou (Afrique, Benin) and Strasbourg (France). Using theoretical tides for Gujarat, we estimated a scale factor of about −814 nm/s2/V for Grav1 (lower-sphere) and about −775 nm/s2/V for Grav2 (upper-sphere). We corrected the influence of atmospheric pressure from the one-second gravity data before switching to the frequency domain. We extracted a total of 53 Earth's Free Oscillations (EFO) modes during the earthquake in Japan and about 47 EFO modes during the earthquake in Chile. We are able to extract the lowest 0S2 spheroidal mode (0.30945 mHz or 54 min) and 0S0 radial mode (0.81439 mHz or 20 min). The longer time series shows individual 0S2 singlets and 0S3 (0.46855 mHz) singlets due to the Coriolis splitting effect. We cross-referenced the frequencies of these modes using the PREM model and previous global observations. The correlation coefficient between the observed and the PREM model for these two events are 0.999 for Japan earthquake and 0.993 for Chile earthquake. This validates the quality of the data useful for low-frequency studies in seismology. We also calculated the relative deviations of our observed fundamental modes with previously determined observed and theoretical values. We found that the relative deviations of our observed free oscillations do not exceed 0.5%, indicating good correlations.
期刊介绍：
Geodesy and Geodynamics launched in October, 2010, and is a bimonthly publication. It is sponsored jointly by Institute of Seismology, China Earthquake Administration, Science Press, and another six agencies. It is an international journal with a Chinese heart. Geodesy and Geodynamics is committed to the publication of quality scientific papers in English in the fields of geodesy and geodynamics from authors around the world. Its aim is to promote a combination between Geodesy and Geodynamics, deepen the application of Geodesy in the field of Geoscience and quicken worldwide fellows'' understanding on scientific research activity in China. It mainly publishes newest research achievements in the field of Geodesy, Geodynamics, Science of Disaster and so on. Aims and Scope: new theories and methods of geodesy; new results of monitoring and studying crustal movement and deformation by using geodetic theories and methods; new ways and achievements in earthquake-prediction investigation by using geodetic theories and methods; new results of crustal movement and deformation studies by using other geologic, hydrological, and geophysical theories and methods; new results of satellite gravity measurements; new development and results of space-to-ground observation technology.
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