利用芦山地震自由振荡信号检验中国大陆超导重力仪的高频特性

2013-04-20发生在四川芦山的地震，是一个震级为Mw 6.6的高角度逆冲型地震，在2.3~5.3 mHz频段激发了微弱的球型简正模信号。芦山地震的自由振荡信号为人们提供了检验中国大陆超导重力仪高频特性的机会。分析了中国大陆现有的5台超导重力仪和部分宽频带地震仪在芦山地震后的观测数据，结果表明，超导重力仪SG057（拉萨）、SG053（武汉）和流动超导重力仪iGrav（武汉）在2~5 mHz频段具有较低的噪音水平，超导重力仪SG065（武汉）、SG066（丽江）具有较高的噪音水平。

Investigation of High-Frequency Noise for Superconducting Gravimeters of China Using Normal Modes of Lushan Earthquake

Given the very low instrumental noise at frequencies below 1 mHz, the superconducting Gravimeter (SG) is a highly sensitive and stable gravimeter for observations of the Earth's tides. As a new generation of SGs is widely used in observations and research on changes of gravity caused by activity in the interior Earth in recent years, the noise level of SGs at high frequency recording band is receiving more and more attention. Weak signals from the free oscillations of the Earth can help us directly investigate the capability of SGs to contribute to geodynamics research. The Lushan Mw6.6 earthquake, on 20 April 2013 in Sichuan, China, generated weak spheroidal modes in 2~8 mHz. We investigated the normal modes recorded by 5 SGs of mainland China, and computed the synthetic normal modes according to the theory of double couple centroid moment tensor based the spherical, non-rotating, elastic and isotropic (SNREI) Earth model. The results show that at the 2~5 mHz frequency band, the SG057 at the Lhasa station, the SG053 and the portable SG (iGrav) at the Wuhan station had a low noise level; the SG65 at Wuhan station and SG66 at Lijiang station had a high noise level. The test method and results can provide the reference when studying the high-frequency noise level of a gravimeter for clearing the application range.