A straight scarp that limits the eastern (outer) margin of T2, and strikes nearly N-S direction, is very distinctive (Figs. 4, 5, and 6). This scarp starts from the Chishan Park at north and continues southward to the west of Pingtung and is ca. 30 km long.
Scarp profile is divided into two types.
Flexural scarp: The first type is typically seen at the Chishan Park (Fig. 9) and
Shangcholi (Fig. 10), and is characterized by the smooth and convex profile without any c
Kaoping River Fault after Shyu et al.(2005) for this fault. We did not f
Figur
lear knick point between the terrace surface and scarp (profiles in Figs. 9 and 10), photo. 2). Tilted gravel bed parallel to the scarp shows that the scarp is not erosional origin but former terrace surface and represents flexural or warping scarp, created by deformation on the hanging wall of subsurface fault. We consider that this fault is a reverse fault with east facing scarp and with westward dipping fault plane, probably high angle, judging from scarp profile and rather straight trace in the northern part.
We use the name of
ind positive evidence to prove the left-lateral offset, proposed by Shyu et al.
(2005) from our field observation. Flexural scarp of this pattern is often recognized on the reverse fault in Taiwan (e.g. Chen et al., 2003; Chang et al., 2004; Ota et al., 2004;
Lai et al., 2006 for the Chulungpu Fault and Ota et al., 2005 for Tunglo Fault). We assume that the base of the scarp represents the location of the fault, although the base is partly buried by Holocene deposits and no fault exposure was found yet. We examined some lineaments found on the alluvial lowland by the photo interpretation, but no evidence of Holocene activity was found in the field.
e 10. Detailed contour map of fluvial terraces and their deformation in the Shangchouli area (drawn by 20 m grid DEM) and flexural scarp deforming T2. Two profiles across T2 on the Shangchouli area aslso clearly show the eastward convex scarp by a buried Kaoping River fault.
The amount of vertical displacement is unable to be exactly determined, because of very gradual change from the original slope to deformed flexural scarp. The possible minimum amount of vertical offset of T2 ranges from 50 to 60 m (profiles a-a’ to d-d’ of Fig. 9, and profile a-a’ , b-b’ in Fig.10). At the Chishan Park, even a local T3 is also deformed, but the amount of vertical offset is about 30 m (profile b-b’
of Fig. 7B), smaller than that of T2, and indicates a progressive deformation since T2 formation.
Erosional scarp modified from flexural scarp: Intensive down cutting and
land-sliding in the mudstone area completely removed terrace remnants for 8 km between Shangchouli and Dapingting (Fig. 5), thus here we cannot identify the tectonic scarp. Southward from Dapingting again T2 is extensively preserved, but scarp morphology is different from Chishan Park and Shangchouli area. There is a sharp knick point between terrace surface and terrace riser, as illustrated in the profile shown in Fig. 11. This is the second type of the scarp, and we interpret that this steep scarp was originally formed as a flexural scarp same as those in the northern area, but now is modified by fluvial erosion of the Kaoping River, because this river flows just base of the cliff. Fig. 12A and B illustrates how profiles are different between the orthern part (tectonic scarp) and the southern part (erosional scarp, modifying riginal tectonic scarp) and how they were formed. Such different profiles as a no
composite result of tectonic and erosional processes are typically preserved in Sado Island, Japan (Ota et al., 1992; Fig. 12C and D). In this study area, the flexural scarp is completely removed, thus we might have difficulty to assume the presence of initial tectonic scarp, unless the preserved flexural scarp at the Chishan Park and Shanchouli.
In the case of Sado Island, main flexural scarp with secondary range-facing scarp is well preserved in the Kuninaka plain (Fig. 12 C). In contrast, the major tectonic scarp is eroded out by marine erosion on the open coast, however, still the preserved range-facing scarp indicates that the present sharp cliff is modified from the initial tectonic scarp (Fig.12 D). This gives us a good analogy of the interpretation for two types of scarp along the Kaoping River. Difference between A, B（Kaoping River fault）and C,D (Sado Island) can be explained by the different fault dip. In the case of Sado Island (C, D), range-facing scarplet and associated tectonic bulge on the hanging wall, as well as the flexural scarp by the main thrust, are characteristic, indicating low angle fault dip. In the case of Kaoping River Fault (A, B), the fault dip is rather high angle to create a characteristic range-facing scarp. An information for subsurface structure is necessary for further interpretation. The original position of the fault is uncertain in the case of the erosional scarp, however, but it is not so far from the present scarp, if extending the base of flexural scarp on the northern part southward.
Estimated length of the Kaoping River Fault is ca.30 km.
Figure 11. Profiles across T2 show erosional scarp on the eastern margin of T2. a-a’ is for Dapingting area and b-b’ is for Dakeng area (See Fig. 6 for the location). The outer margin of terrace is sharply limited by steep scarp. The location of supposed buried scarp seems to be apart from the base of the scarp.
Figure 12. Schematic profiles of warping scarp (A) and erosional scarp (B) modified from initial warping scarp by the Kaoping River Fault. Compare with similar example from Japanese reverse fault shown in C and D (after Ota et al., 1992).
It is difficult to estimate slip rate of Kaoping River Fault, firstly because of rtainty of terrace age, and secondly due to uncertainty of actual amount of vertical offset. On the hanging wall, the inner edge of T2 may be higher than the original terrace height by covering of alluvial fan deposits, and alluvial deposits bury the initial correlative surface on the foot wall. In addition dip angle of fault plane is unknown. Adopting our tentative correlation of T2 with MIS 5e, and several tens of meter for the vertical separation, the slip rate may be an order of 0.5+- m /ka for Kaoping River Fault, and its activity has been repeated.