You can picture riven as a log that has been split with a wedge rather than cut with a saw. The crack follows the wood's own grain, so it opens along a line that was already inside the wood, and the two faces are rough. Hold that picture and the harder use follows: a group can crack the same way, along lines that were already inside it.
The packet's source gives riven as the past participle of the verb rive, from Middle English riven, and points to Old Norse rífa, to tear or scratch. Tearing has been the picture from the start.
來源記到 riven 是動詞 rive 的過去分詞，來自中古英文的 riven，並跟古北歐語的 rífa（撕、抓）有關。所以「撕開」這個畫面從一開始就在這個字裡面，不是後來才加上去的。
Wiktionary 'riven' etymology supplied in this packet (source_ref kaikki:3f6f69a190036ae4:978501163)
From the picture
一群人被劈開
同一把斧頭，落在人的身上：把社團、公司、國家當成一塊木頭，意見就是那道順著內部紋理裂開的縫。所以 riven 比 divided 重，它強調裂痕來自裡面，而且很深。
adjective · C2
Used about a group, a country or an organisation that has been deeply split by angry disagreement between the people inside it, so that its parts are set against each other.
被撕裂的、分裂的
adjective · C2
Split or torn into two or more pieces, usually along a natural line in the wood, the stone or the material itself.
被劈開的、裂成兩半的