Free oscillations of the earth

Japanese: 地球自由振動 - ちきゅうじゆうしんどう（英語表記）free oscillations of the earth

Just as a bell rings with a specific tone when it is struck, when the Earth is vibrated, only vibrations of a specific frequency, i.e., its natural vibration, are produced. This is called the Earth's free oscillation. When a major earthquake occurs, the entire Earth continues to vibrate for several weeks. This vibration is recorded by long-period seismometers. Just as the pitch of a bell depends on the elasticity and density of the bell, the period of the Earth's free oscillation is determined by the Earth's internal structure. The Earth's free oscillation was first observed during the 1960 Chilean earthquake, and has since been used to study the Earth's internal structure and the motion at the epicenter of earthquakes.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

鐘をつけば鐘が固有の音で鳴るように，地球を振動させると，特定の振動数の振動，すなわち固有振動のみが発生する。これを地球自由振動と呼ぶ。巨大な地震が発生すると，数週間もの間，地球全体が振動しつづける。この振動は長周期地震計によって記録される。鐘の音の高低が鐘の弾性や密度によるのと同様に，地球自由振動の周期は地球の内部構造によって決まる。地球の自由振動は1960年チリ地震の際に初めて観測され，それ以後，地球内部構造の研究や地震の震源における運動の研究に用いられている。

出典　株式会社平凡社世界大百科事典第２版について　情報

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