Microseisms

…(2)In electrical engineering, when a direct current is superimposed on an alternating current, it is said to be pulsating, and such a current is called a ripple current. (3)In seismology, microseisms are constant vibrations of the ground that have a relatively simple waveform and a nearly constant period, and continue for a long time while their amplitude repeatedly increases and decreases. Ordinary pulsations have a period of about 3 to 7 seconds, and their amplitude varies greatly depending on the location, being generally larger near the sea and fluctuating simultaneously over a wide area depending on the roughness of the sea, but they can be recorded constantly anywhere in the world using a highly sensitive seismometer. …

*Some of the terminology explanations that mention "microseisms" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…(2)電気工学では，直流に交流成分が重なっているとき脈動しているといい，このような電流を脈流ripple currentと呼ぶ。(3)地震学でいう脈動microseismsとは，地面の常時微動のうち，周期がほぼ一定の比較的単純な波形の振動が，振幅の消長を繰り返しながら長時間続くものをいう。ふつうの脈動は，周期が3～7秒程度，振幅は場所によって大幅に異なり，海に近い所で概して大きく，また海の荒れぐあいに応じて広域にわたって同時に変動するが，高感度の地震計を用いれば，世界中どこでも常に記録される。…

※「microseisms」について言及している用語解説の一部を掲載しています。

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