近年來西南部麓山地區地震頻繁， GPS與相關的地震研究均顯示此區
累積極大的應變潛能，且觸口斷層沿線斷層地形特徵相當明顯，顯示其具
有相當的活動性。由於構造壓縮變形逐漸向西傳遞推移的結果，在前陸的
平原及丘陵區可能存在前峰斷層撓曲或盲斷層作用，潛藏極大的危害。本
文利用構造地形分析角度探討西南部麓山帶的地形分區( zoning )，以作
為斷層分段(segmentation)的基礎。並以斷層形貌特徵表現及斷層幾何、
斷層型態、構造不連續性，加上相關地球物理資料，作斷層活動性及斷層
分段的探討，使未來進一步地震危害評估有更合理的依據。

研究結果顯示，觸口斷層北段與南段，崙後斷層及竹頭崎斷層的中、南段
，以及獺頭斷層的北段，斷層形貌特徵與線型構造均相當明顯。影像構造
判釋顯示，九芎坑斷層於地表出露的位置可能比地質圖更往西偏移且可延
伸至八掌溪以南，觸口斷層於松腳附近出露的位置可能更為偏北。另外，
本研究首次發現在松腳附近一約 4平方公里的崩塌地及至少三次的崩塌記
錄，在牛稠溪山麓沖積口處的河階亦辨認出四個地形面，顯示此區有多次
活動的記錄。此外，斷層前緣以西的紅土台地礫岩及礫岩層上，影像組織
呈斑點狀且具許多走向無明顯規則的密集線型，地震記錄亦顯示有集中情
形，是否具新構造上的意義，尚需進一步探討。地形分析的結果，可將研
究區域劃分為八大地形區、十八個地形次區及二十六個微地形區。根據地
形分析及地形分區資料所顯示的結果，配合層位落差及相關地質資料，將
觸口斷層分成斗六丘陵段( 14.4 km)、牛稠溪至八掌溪段(7.8 km)及八掌
溪以南段(24 km)，各分段的最大可能地震規模，分別為斗六丘陵段M=5.9
、牛稠溪至八掌溪段M=5.3、八掌溪以南段M=6.4。

The foothills belt of southwestern Taiwan is a zone of
active deformation based on the frequency of
earthquake events and GPS(Global Position System) geodetic
data. The thrust front propagates westward beneath the
coastal plain, and these blind faults and folds are,
therefore, potential natural hazards to the populated area. This
study applies tectonic geomorphology to study the
topographic zoning of southwestern foothills belt. By
studying topographic characteristics, geometric and
structural discontinuity, and geophysical data, the
research results can provide a basis for fault segmentation and
better estimation of the fault magnitude.

The lineament and characteristic features of faults are dominant
in the northern and southern part of the Chukou fault,
middle and southern part of the Lunhou Fault and southern
part of the Chutouchi Fault. Base on structural
interpretation of satellite images, the surface position of
the Chiuhsiunghen fault may be farther west, than shown in the
geology map, and the Chiuhsiunghen fault may extend to the Pa
Chang Hsi. Further more, a 4 km2 landslide which records at
least three times' activity appear east of Chu Chy. This coupled
with four stream terraces at the mountains' alluvial fan of
Niu Ch'o Hsi indicate that this area is active. Drainage
andleveling data also indicates a rapid increase of uplift rate
from coastal plain toward foothills across the Chukou Fault.
The spotty texture of terrace and lateritic terrace
deposits as shown in the image, dense lineaments and the
earthquake activity may indicate a blind thrust in this area.

Results of topographic analysis separate the study area into
eight main geographic zones, eighteen topographic sub-zones
and twenty-six micro zones. According to topographic
analysis, stratigraphy separation and related geologic data,
the Chokou fault can be delineated into Tou-Liu mountain front
segment (14.4 km), the Niu-Ch'o Hsi to Pa-Chang Hsi
segment (7.8 km) and the segment south of Pa-Chang Hsi (24 km).
The possible earthquake magnitude associated with these
three segments from north to south are M=5.9, M=5.3,
M=6.4 respectively.