利用地球自由振荡信号分析湖北地震台网地震仪低频特性

2011年日本东北部太平洋海域发生MW9.0特大地震，国际上很多著名地震科研机构和学者发布了不同的震源机制解，很多学者也对这些震源机制解进行了评价。选取其中较优的GCMT震源机制解计算模拟日本大地震激发的自由振荡信号，并与湖北地震台网的15个地震仪观测结果进行对比，进而评价各个地震仪在低频段的观测情况以及分析地震仪在不同频段的观测能力。结果表明，总体来说，在1.5~4.5 mHz频段，地震仪观测到的自由振荡信号与理论模拟值符合度较高；在小于1.5 mHz频段，地震仪整体的观测能力不佳；而在大于4.5 mHz频段，观测值振幅明显要低于模拟信号的振幅，表明在该频段信号的实际衰减要比PREM地球模型中衰减快。另外，基于1.5~4.5 mHz频段的球型简正模评估15个地震仪的观测状况，结果表明，大部分的地震仪观测情况较好，有10个台站的观测值与模拟值的符合度在90%以上；而YC、NZH、DJI等台站的符合度较差，其中DJI符合度最差，为0.358。

Investigation of Low Frequency Characteristics of the Hubei Earthquake Network Seismograph Using Earth’s Free Oscillation

An MW9.0 earthquake occurred near the Pacific coast of Tohoku, Japan on March 11, 2011. Many internationally well-known research institutions and scholars launched different earthquake focal mechanism solutions, with many scholars evaluating these solutions. We simulate the free oscillation signal excited by the Japan earthquake. Comparing 15 seismograph observations of the seismic network in Hubei, we evaluate observations of these seismographs in low frequency band and analyze the observation ability in different frequency bands. The results show that in the 1.5 mHz to 4.5 mHz bands, there is excellent agreement between observations and synthetics; in >4.5 mHz bands, observed amplitude is significantly lower than in synthetics. In addition, we assess the observational conditions of instruments based on the spheroidal modes in the 1.5 mHz to 4.5 mHz band: most of the seismograph observation conditions are good; the conformity to simulation value and the observed value of 10 stations is up to 90%; the conformity of YC, NZH, DJI is poor.