梨山斷層，為台灣一條重要的構造線，分隔了雪山山脈及中央山脈二個構造帶。許多研究指出，梨山斷層北起於蘭陽盆地，但向西南深入山區後，由於受限於交通不易到達，絕大部分並無完善的測量資料，使得梨山斷層的南段在玉山以南即不太明確。本研究將依地球物理中的重力測量方法來推估南橫天池至啞口區段中的地下岩層性質與地下構造，及其與梨山斷層的關係。
由117個在南橫天池至啞口路段間的利用重力儀所測得的重力資料,經過資料校正後得到本研究區的布蓋重力異常值分佈圖、分佈剖面及各剖面所建構的基岩構造模型來判斷其地下構造。資料校正包含了儀器修正、緯度修正、自由空間修正、布蓋修正及地形修正。根據本研究建構的模型指出，此區的岩層密度大約界於2.5-3.2 g/cm3。
由模型可知，此區大部分為向西傾的斷層構造。再由從模擬的數據來看，如果梨山斷層穿過這個區域，它亦可能為一個向西傾斜背衝斷層。本研究區域中其他主要斷層亦由重力法指出為大關山斷層及兩個不知名的斷層。

Lishan Fault, an important structural line in central Taiwan, separates two tectonic provinces - the Hsuehshan Range and the Backbone Range. Many studies have indicated that the Lishan Fault is exposed in the Lanyang Basin of northeastern Taiwan, but toward the south into the mountains where access is limited due to rugged topography, the strike of the southern portion of the Lishan Fault is unclear. In this study, gravity surveying is used to examine the possible occurrence of the Lishan fault in the area between Tienchih and Yakou area and to map other important faults as well.
One-hundred and seventeen gravity stations were surveyed along the road between Tienchih and Yakou with a Worden gravimeter. A contour map, profiles, and basement models of Bouguer anomaly were constructed to aid in fault identification in the project area. Data reductions included: drift correction, latitude correction, free-air correction, Bouguer correction and terrain correction. Modeled densities ranged from 2.5 to 3.2 g/cm3.
From the models, most of the formations in the study area are west-dipping. From the modeled data, if the Lishan Fault passes through this area, it is possibly a west-dipping backthrust fault. Other major faults in this area that were identified by the gravity method include Daguanshan fault and two unnamed faults.

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