利用全台网垂直摆倾斜仪数据检测日本Mw9.0地震激发的低频自由振荡

摘要

首次利用全台网多台垂直摆倾斜仪观测数据检测地球自由振荡.2011年日本Mw9.0大地震发生后,43台仪器记录到其所激发的自由振荡信号.谱分析结果显示,垂直摆倾斜仪检测到了低频段(1～5mHz)地球自由振荡振型,并且在超低频部分(＜1.5 mHz)仍然还有较高的信噪比.选取43个台站中观测质量较好的36个台站数据进行叠积以增强信号,可以探测到一些非常微弱的模态,最终得到频率高于4.7 mHz的所有零阶球型振荡0S3～0S38(其中7个振型的观测频率与理论值的偏差近似为0)和环型振荡0T3～0T28几乎所有振型,此外还检测到21个谐频振型.%After the 2011 Tohoku Mw9.0 earthquake,43 vertical pendulum tiltmeters recorded the Earth's free oscillation signals that were excited by the great earthquake.We find that the tiltmeters have a special sensitivity to detect low-frequency Earth's free oscillation (1～5 mHz).Even in very low frequencies (＜1.5 mHz),the modes can be identified with high SNR.We select 36 records out of 43 stations in this study.Using signal enhancement methods (product spectrum over 36 records),even the gravest modes are detected.All of the spheroidal oscillation modes (0S3 ～0S38) and almost all of the toroidal oscillation modes(0T3 ～0T28) and 21 harmonic modes are observed.