aseismic ridge

... refers to a long, narrow seafloor rise with steep slopes on both sides (see Figure 1 in the "Submarine Topography" section). They are divided into mid-oceanic ridges, where a series of shallow earthquakes has been observed along the central axis and it is clear that the seafloor is being created and spreading, and aseismic ridges, where no series of seismic activity has been observed and the rocks in the central axis are old. The long, large rise seen in the southeastern Pacific Ocean has a relatively gentle slope and is smoothly undulating, so it is called the East Pacific Rise, but in terms of origin, it is also a type of mid-ocean ridge.

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

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…細長くて幅が狭く，こう配の急な斜面を両側に有する海底の高まりをいう(〈海底地形〉の項目の図1参照)。中軸沿いに浅い地震の列が観測され，海底が生成･拡大しつつあることが明瞭な大洋中央海嶺mid‐oceanic ridgeと，地震活動の列がみられず，中軸部の岩石の年齢も古い非活動海嶺aseismic ridgeとに分けられる。太平洋の南東部に見られる長大な高まりはこう配が比較的ゆるく，起伏もなめらかなので東太平洋海膨とよばれるが，成因的にはこれも大洋中央海嶺の一種である。…

※「aseismic ridge」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