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Figure 4. Turning of the tributaries for drag effects along 
the Cayambe-Chingual Fault. Distortion of the 
hydrographic pattern is consistent with the right-lateral 
strike-slip motions detected on the slickenside fault 
planes. Location on Figure 2. 
southward. Measurements of dislocation amount was 
extended to all these faults and a checking was made on 
the faults recognized on the satellite images. As an 
example, the CCF produces an off-set of 1 km in late 
Pleistocene lava flow (Fig. 5). The resulting dislocation 
rate of 6 mm/yr (considering 0.16 Ma a representative 
age for the lava flow) could be consistent with that one 
measured by the satellite images. Absolute datings could 
help to constrain these data. Field checks showed that 
the minimum amount of dislocation usually recognized 
was of the order of 3-4 m, and confirmed that the 
escarpments were due to strike-slip or reverse faulting in 
the eastern Andes and to normal motions in the IV. 
These data are consistent with the widespread seismic 
activity comprising 7 large earthquakes (estimated 
intensity of Mercalli scale > IX) occurred in the study 
area (Fig. 6, Observatorio Astronomico de Quito, 1959). 
4. LANDSLIDE MAPPING 
Several small landslides are located along the major 
active faults (example in Fig. 5). This distribution is 
consistent with the presence of active tectonic motions 
along these faults. Several other landslides of various size 
have been triggered by the 1987 earthquake and are 
widespread in the north-eastern EA. The landslides are 
easily distinguishable on the various images and photos 
for the high difference of reflectance between the 
outcropping rocks and the surrounding jungle. The 1987 
landslides were mapped on aerial stereophotos to obtain 
the maximum amount of data. The limit of each landslide 
was digitized and the affected area was calculated, using 
a grid cell of 1 sq. km (Fig. 7). The isolines, expressed as 
percentage of landslided area respect to the cell area, 
define a NNE elongated zone which is coincident with the 
276 
active faults (Fig. 2), with the shape of the areas affected 
by  microseismicity recorded during the periods 
January-April 1981 (1 in Fig. 6) and December 
1986-March 1987 (2 and 3 in Fig. 6) (Barberi et al., 1988) 
  
    
  
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Figure 5. Geomorphic and geological indicators of recent 
motions along the Cayambe-Chingual Fault. 1. Recent 
lava flow; 2. fault trace; 3. triangular facets; 4. landslide 
scarp; 5. large landslide scree-tongue. Location on 
Figure 2. 
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