斷層下盤陷落池A Sag Pond along the Chihshang Fault

逆斷層的特性，使得池上斷層除了斷層帶擠壓破裂變形外，斷層上盤持續往上抬升、下盤則相對向下陷落。一般而言，在斷層相對陷落的一側，偶而可以觀察到低地，甚至一些水池。這些低地或水池的成因，與斷層的活動及斷層兩側地塊的相對位移，有非常密切的關係；地質學家即稱之為斷層「陷落池」。

以大坡池為例，它位於池上斷層的下盤，在靠近斷層處，不斷往下陷落。同時它又位於兩個小沖積扇之間（大坡溪沖積扇在北，錦園溪沖積扇在南），形成了一個天然的溪水的聚集盆。另外縱谷的平坦，也使得大坡池在過去沒有人為渠道整治前，它的範圍在豐水期時可以比現在的範圍大上許多。

The Tapo Pond has a strong correlation with the Chihshang Fault. As the Chihshang Fault continuing to move, the hanging wall is uplifting and the footwall is subsiding. As a result, the Tapo Pond seems to represent a sag pond, which is common along active fault, in the subsiding footwall of the Chihshang Fault. The location of the Tapo Pond is located at a topographic low in-between two small alluvial fans (the Tapo river alluvial fan to the north and the Chinyuan river alluvial fan to the south), also favoring the development of the sag pond. It appears that the Tapo Pond was much bigger before the channelization for agriculture water usage since several decades ago.