1, Regional Geology

The Chaochou fault is located on the eastern of Pingtung plain that is the major tectonic line dividing the Central Range and the Western Foothills. The river is deposited a series alluvial fan on the frontal Central Range in the north of Ailiao River. Most of the fault trace is covered by the Holocene alluvium resulting in unobvious topographic expression. In general, the fault trace is roughly along the western part of lateritic alluvial-fan terrace (Chingyeh fan terrace) (Figure 1).

Figure 1, The Chaochou fault is situated on the western of terrace scarp.

2, Fault Character

The Chinyeh-terrace section (Figure 2) shows that the lateritic terrace gravels (Figure 3) and a conglomerate formation unconformably overlain on a late Pleistocene shale (Figure 4). The shale formation is unconformably deposited on the slate formation of the Central Range. The relationships between the three units of sedimentary strata appear that this area occurred syn-tectonic deposition near the Chaochou fault tip, forming a growth fold. Three core-borings (CY-1, CY-2, CY-3) are located on the terrace scarp. The bring log occurred intensive shear plane within the shale formation which is unconformably overlie by the conglomerate formation (Figure 5).

Figure 2, The Chingyeh-terrace section shows the relationship between three depositional units of terrace gravel bed, conglomerate, and shale.

Figure 3, The terrace gravel is unconformably deposited on the shale formation.

Figure 4, The conglomerate is unconformably deposited on the shale formation.

Figure 5, Lithologic character of the CY-1, CY-2, and CY-3 core-borings.