Edge elements for collapsed buildings ( C-1, 2,3), nondamaged buildings (N-1, 2, 30 and bare ground (G-1) were detected. The intensities of edge elements were calculated by a general gradient filter with a 3x3 pixel window and were allocated a 1 byte value. The relationship between the edge intensity value and the cumulative percentage of relative frequency is shown in figure 4. on observing he data for nondamaged building 9 N-1) and ground ( G_1), it is found that their edge intensity values are almost all distributed in the range of 0-32. for collapsed buildings ( C-1, 2,3 ), it is found that the intensity values are almost all ( 95%) distributed in the range of 0-90.

Area no.	Degree of building damage	Number of pixels	Remarks
C-1	Collapse (rubble)	2758	A wooden building
C -2	Collapse (rubble )	7951	A wooden building
C -3	Collapse (rubble )	15321	A wooden building
N-1	No damage	10000	The roof of a gymnasium with dark green color
N-2	No damage	14695	The roof and wall of a wooden building with white color
N-3	No damage	7649	A building of complicated shape with brown roofs.
G-1	Ground	5400	A bare ground

Table 1 The Characteristics of selected buildings



Figure 3 The selected buildings and areas



Figure 4 Relationship between edge intensity value and cumulative percentage of relative frequency



Figure 5 Relationship between variance value of edge intensity and cumulative percentage of relative frequency