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Figure 2. Remotely-sensed (Landsat, SLAR and aerial 
stereophotos) main recent and active faults of the 
Ecuadorian Andes checked in the field. Histograms show 
total number of remote-sensed faults (Y axis) versus 
azimuth (X axis) for northern (A), central (B) and southern 
(C) part of the area. Faults: 1 normal, 2 strike-slip, 3 
oblique-reverse, 4 reverse, 5 pivotal, CCF 
Cayambe-Chingual, LBF La Bonita, PF Paillatanga, A, B, 
C and D referred in the text. Volcanoes: 6 Quaternary, 7 
caldera, 8 collapse rim, VC Cayambe, VR Reventador, VA 
Antisana, VCH Chimborazo. Boxes: square - figure 4; 
rectangle = figure 5. 
Seven main faults with paleoseismic characteristics in the 
EA were discovered on satellite images. The 
Cayambe-Chingual Fault (CCF in Fig. 2), named after 
Tibaldi (1990), can be followed on the image for 76 km. 
Along the majority of this fault trace, dislocation of river 
streams and gouges can be measured (Fig. 3), giving a 
mean value of 360 m. The high altitude of the studied 
area, ranging between 2,000 and more than 4,000 m, is 
consistent with the assumption that landforms were 
inherited from the last main glacial pulses (11,000 + 1,000 
yr BP for the areas > 3,800 m, 27,500 + 7,500 yr BP for 
the areas > 3,000 m, Clapperton and Vera, 1986). 
Considering that the majority of the CCF outcrops 
between 2,700 and 3,500 m, its horizontal rate of tectonic 
275 
motions may be estimated to be 13 « 2.7 mm/y. The type 
of faulting was strike-slip right-lateral, according to the 
sense of river dislocation. The coregistration of this fault 
trace on the topographical map shows that the analysis 
on the satellite data is correct both for sense and amount 
of dislocation (fig. 3 and 4). The same features were 
discovered along the La Bonita fault (LBF in Fig. 2). Here 
the Holocene fault motion rate is quite uncertain because 
only two dislocation amounts have been measured (Fig. 
3). 
Southward, only a segment of an active N-S fault was 
recognized on satellite images (site A in Fig. 2). An 
escarpment facing westward dislocates glacial 
morphologies of the last pulse revealing relative upward 
motions of the east block. Topographic data indicates 
along this segment a total amount of vertical dislocation 
of about 30 m (a rate of 2.7 + 0.2 mm/y). 
More southward, the eastern Andes are occupied by 
large volcanoes until the latitude of 2?S. South of this 
area, a fault with the same characteristics of the CCF can 
be traced for about 100 km. This fault, named Paillatanga 
Fault after Winter and Lavenu (1989) (PF in Fig. 2), shows 
an average dislocation of crests and river streams of 45 
m (a rate of 4 + 0.3 mm/y) (Fig. 3). Motions were 
strike-slip right-lateral and fault strike goes from NNE to 
NE. 
In the IV some N-S escarpments bordering depressed 
areas infilled by alluvial or pyroclastic rocks have been 
recognized on satellite images. The total amount of 
vertical dislocation is of about 200 m for the fault labelled 
B in Fig. 2, 150 m for C and 80 m for D. 
Using radar images and aerial stereophotos other 36 
active faults were discovered (Fig. 2). For example, the 
segment A was recognized as belonging to a longer NNE 
fault with a vertical dislocation diminishing northward and 
  
400 
3504 
3004 
2504 
200 4 
150- VER ud fct 
100 4 
BO a AN Valle an Ë 
= 
9 1 i i 4 
Figure 3. Examples of dislocations in meters (Y axis) 
measured at different points along some main active 
faults of the Ecuadorian Andes (X axis) on remote sensed 
images (1 =Cayambe-Chingual Fault,2 =La Bonita Fault, 
4 = Paillatanga Fault) and with topographical data 
(3= Cayambe-Chingual Fault). 
  
  
  
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