Application of geospatial technologies for multi-hazard mapping and characterization of associated risk at local scale

Figures & data

Table 1. Ward-wise description of Gangtok city (highlighted portion shows the representative site for risk analysis).

Ward Code	Name of the Ward	Area (km^2)
001	Upper Burtuk	2.625
002	Lower Burtuk	1.610
003	Lower Sichey-I	2.050
004	Lower Sichey-II	1.081
005	Upper Sichey	0.681
006	Chandmari	2.911
007	Development Area	0.710
008	Diesel Power House	0.212
009	Arithang	0.353
010	Lower M.G. Marg	0.142
011	Upper M.G. Marg	0.133
012	Tibet Road	0.329
013	Deorali	0.313
014	Daragaon	1.600
015	Tadong	1.250
016	Ranipool	1.217
017	Syari-Tathangchen	2.166
	Total	19.38

Figure 1. Location map of the study area.

Figure 2. Methodology used to carry out multi-hazard risk analysis (a) section represents the hazard analysis, (b) represents the vulnerability assessment, (c) shows the future approach for multi-hazard risk analysis.

Table 2. Standardized score and weights for different building vulnerability factors.

Analysis	Factors	Factor’s subclass	Weight	Raw score	Standardized score
Earthquake
Building vulnerability	Building material	Asbestos	3	2	0.75
		RCC		1	0.25
		Bamboo		4	1.00
		Wood		3	0.50
	Building floors	1	2	1	0.33
		2		2	0.66
		>3		3	1.00
	Building ownership	Private	1	2	1.00
		Government		1	0.50
Landslide
Building vulnerability	Building ownership	Private	1	2	1.00
		Government		1	0.50
	Building use	Residential	2	1	0.17
		Hotel/guest house		6	1.00
		Office/business		5	0.83
		Industry		4	0.67
		Temple		2	0.33
		Others		3	0.50
	Building material	Asbestos	4	3	0.75
		RCC		1	0.25
		Bamboo		4	1.00
		Wood		2	0.50
	Building floors	1	3	2	1.00
		More than 1 floor		1	0.50

Figure 3. (a) Building vulnerability map for earthquake hazard, (b) building vulnerability map for landslide hazard.

Figure 4. Lifeline vulnerability: (a) road vulnerability due to earthquake (b) road vulnerability due to landslide.

Figure 5. Human vulnerability: (a) for earthquake, (b) for landslide.

Table 3. Pair-wise comparison matrix of earthquake influencing factors.

Conditioning factors	Soil liquefaction	PGA	PAF	Resonance frequency	Geology	Fault	Slope morphometry	LULC	Soil thickness	Normalized weights
Soil liquefaction	1.00	0.33	0.33	3.00	8.00	5.00	8.00	7.00	8.00	0.17
PGA		1.00	2.00	3.00	9.00	9.00	9.00	9.00	9.00	0.30
PAF			1.00	5.00	9.00	6.00	9.00	9.00	9.00	0.27
Resonance frequency				1.00	9.00	2.00	9.00	5.00	9.00	0.11
Geology					1.00	0.20	1.00	0.20	0.33	0.02
Fault						1.00	7.00	3.00	3.00	0.06
Slope morphometry							1.00	0.25	0.33	0.02
LULC								1.00	3.00	0.04
Soil thickness									1.00	0.02

Principal eigen value = 10.05, consistency ratio (CR) = 0.09.

Table 4. Pair-wise comparison matrix of landslide influencing factors.

Conditioning factors	Slope morphometry	Aspect	Curvature	Geology	Lineament	Soil	Soil thickness	LULC	NDVI	Water regime	Normalized weight
Slope morphometry	1.00	8.00	7.00	2.00	7.00	5.00	3.00	4.00	3.00	2.00	0.25
Aspect		1.00	0.50	0.14	0.50	0.33	0.33	0.25	0.20	0.17	0.02
Curvature			1.00	0.14	1.00	0.33	0.50	0.33	0.20	0.20	0.03
Geology				1.00	5.00	3.00	5.00	6.00	3.00	2.00	0.21
Lineament					1.00	0.33	0.50	0.33	0.20	0.20	0.03
Soil						1.00	2.00	2.00	0.50	0.33	0.07
Soil thickness							1.00	1.00	0.33	0.33	0.05
LULC								1.00	0.33	0.25	0.05
NDVI									1.00	0.17	0.10
Water regime										1.00	0.19

Principal eigen value = 10.63, consistency ratio (CR) = 0.04.

Table 5. Weights, eigenvector values and consistency ratio (CR) of the earthquake hazard derived from pair-wise comparison matrix.

S. no.	Factors	Weight (Wj)	PEV and CR	Subclass	Rank (Wij)
1	Soil liquefaction (Source: SSDMA)	0.168	Principal eigen value (PEV) = 4.17, consistency ratio (CR) = 0.06	Very high	0.56
				High	0.31
				Medium	0.09
				Low	0.04
2	PGA (Source: SSDMA)	0.302	Principal eigen value (PEV) = 6.39, consistency ratio (CR) = 0.06	Low	0.03
				Medium low	0.06
				Medium	0.07
				Medium high	0.08
				High	0.29
				Very high	0.48
3	PAF (Source: GSI)	0.266	Principal eigen value (PEV) = 5.28, consistency ratio (CR) = 0.06	0–2	0.03
				2–4	0.05
				4–6	0.11
				6–8	0.24
				8–10	0.56
4	Resonance frequency (Source: GSI)	0.112	Principal eigen value (PEV) = 8.91, consistency ratio (CR) = 0.09	<2	0.02
				2–4	0.02
				4–6	0.03
				6–8	0.05
				8–10	0.09
				10–12	0.12
				12–14	0.30
				>14	0.37
5	Geology (Source: GSI)	0.015	Principal eigen value (PEV) = 5.41, consistency ratio (CR) = 0.09	Darjeeling gneiss	0.04
				Coarse grained garnet mica schist	0.10
				Garnet mica schist with phyllite	0.18
				Phyllite and schist with interbands	0.64
				Lingtse granite gneiss	0.04
6	Slope morphometry (Source: SSDMA)	0.015	Principal eigen value (PEV) = 6.35, consistency ratio (CR) = 0.05	Very high	0.03
				Gentle	0.03
				Moderate	0.06
				High	0.12
				Steep	0.25
				Critical	0.51
7	Fault (Source: GSI)	0.059	Principal eigen value (PEV) = 2, consistency ratio (CR) = 0.00	Yes	0.90
				No	0.10
8	LULC (Source: LISSIV)	0.038	Principal eigen value (PEV) = 5.28, consistency ratio (CR) = 0.06	Forest	0.03
				Agriculture	0.06
				Agriculture and sparse population	0.12
				Sparse population	0.23
				Dense population	0.56
9	Soil thickness (Source: SSDMA)	0.024	Principal eigen value (PEV) = 6.46, consistency ratio (CR) = 0.07	Thin soil cover	0.03
				Thin soil cover with slope	0.10
				Thin to medium thick soil cover	0.11
				Medium thick to thin soil cover	0.10
				Medium thick soil cover	0.30
				Thick soil cover	0.36

Table 6. Weights, eigenvector values and consistency ratio (CR) of the landslide hazard derived from pair-wise comparison matrix.

S. no.	Factors	Weight (Wj)	PEV and CR	Subclass	Rank (Wij)
1	Slope morphometry (Source: SSDMA)	0.25	Principal eigen value (PEV) = 6.33, consistency ratio (CR) = 0.05	Very gentle	0.03
				Gentle	0.03
				Moderate	0.05
				High	0.19
				Steep	0.35
				Critical	0.35
2	Aspect (Source: CartoDEM)	0.02	Principal eigen value (PEV) = 9.6, consistency ratio (CR) = 0.05	Flat	0.02
				North	0.03
				Northeast	0.09
				East	0.27
				Southeast	0.21
				Southwest	0.06
				West	0.14
				Northwest	0.08
				South	0.08
3	Curvature (Source: CartoDEM)	0.03	Principal eigen value (PEV) = 3, consistency ratio (CR) = 0.007	Concave	0.45
				Flat	0.06
				Convex	0.49
4	Geology (Source: GSI)	0.21	Principal eigen value (PEV) = 5.1, consistency ratio (CR) = 0.02	Darjeeling gneiss	0.08
				Coarse grained garnet mica schist	0.13
				Garnet mica schist with phyllite	0.22
				Phyllite and schist with interbands	0.54
				Lingtse granite gneiss	0.04
5	Lineament (Source: GSI)	0.03	Principal eigen value (PEV) = 4.16, consistency ratio (CR) = 0.06	Low	0.04
				Medium	0.08
				High	0.29
				V high	0.58
6	Soil (Source: SSDMA)	0.07	Principal eigen value (PEV) = 5.04, consistency ratio (CR) = 0.009	Debris comprises mostly rock pieces with sands younger loose material	0.44
				Debris comprises mostly rock pieces older sand	0.27
				Sandy soil with naturally formed surface	0.16
				Older well compacted mature soil formation	0.04
				Clayey soil with naturally formed surface	0.08
7	Soil thickness (Source: SSDMA)	0.05	Principal eigen value (PEV) = 6.23, consistency ratio (CR) = 0.03	Thin soil cover	0.15
				Thin soil cover with slope	0.12
				Thin to medium thick soil cover	0.32
				Medium thick to thin soil cover	0.21
				Medium thick soil cover	0.17
				Thick soil cover	0.04
8	LULC (Source: LISSIV, 2016)	0.05	Principal eigen value (PEV) = 5.31, consistency ratio (CR) = 0.06	Forest	0.04
				Agriculture	0.06
				Agriculture and sparse population	0.10
				Sparse population	0.28
				Dense population	0.51
9	NDVI (Source: LISSIV, 2016)	0.10	Principal eigen value (PEV) = 5.17, consistency ratio (CR) = 0.03	−0.38	0.53
				0.18	0.22
				0.27	0.14
				0.36	0.07
				>0.36	0.03
10	Water regime (Source: SSDMA)	0.19	Principal eigen value (PEV) = 4.07, consistency ratio (CR) = 0.02	Subsurface/low surface regime	0.05
				High	0.11
				Medium	0.26
				Dry	0.58

Figure 6. Hazard zonation map of (a) earthquake and (b) landslide.

Table 7. Buildings likely to be affected for different landslide hazard classes.

			Hazard classes
Factor	Factor subclases	Hazard type	Low	% of building type	Moderate	% of building type	High	% of building type	Very high	% of building type	Total per type
Building ownership	Private	Landslide	285	54.9	181	34.8	38	7.3	15	2.9	519
		Earthquake	301	62	183	37.5	4	1	–	–	488
	Government	Landslide	10	62.5	6	37.5					16
		Earthquake	12	86	2	14.2	–	–	–	–	14
Building use	Residential	Landslide	268	54.5	174	35.4	36	7.3	14	2.8	492
		Earthquake	281	61	179	39	3	0.6	-	-	463
	Hotel/Guest house	Landslide	7	53.8	6	46.2					13
		Earthquake	14	100	–	–	–	–	–	–	14
	Office/Business	Landslide	9	75.0	1	8.3	1	8.3	1	8.3	12
		Earthquake	11	91	1	8.3	–	–	–	–	12
	Industry	Landslide	3	60.0	1	20.0	1	20.0	–	–	5
		Earthquake	2	50	2	50	–	–	–	–	4
	Temple	Landslide	1	100	–	-	–	–	–	–	1
		Earthquake	1	100	–	-	–	–	–	–	1
	Others	Landslide	7	53.8	3	23.1	–	–	3	23.1	13
		Earthquake	4	57.1	2	28.5	1	14.2	–	–	7
Building material	Asbestos	Landslide	6	35.3	5	29.4	4	23.5	2	11.8	17
		Earthquake	11	65	6	35.2	–	–	–	–	17
	RCC	Landslide	277	60.0	165	35.7	16	3.5	4	0.9	462
		Earthquake	264	61	166	38.2	4	1	–	–	434
	Bamboo	Landslide	2	20.0	4	40.0	–	–	4	40.0	10
		Earthquake	5	100	–	–	–	–	–	–	5
	Wood	Landslide	10	20.0	13	26.0	18	36.0	9	18.0	50
		Earthquake	33	72	13	28.2	–	–	–	–	46
Building floors	1	Landslide	108	47.6	76	33.5	30	13.2	13	5.7	227
		Earthquake	124	58	86	40.1	4	1.8	–	–	214
	More than 1	Landslide	187	60.7	111	36.0	8	2.6	2	0.6	308
		Earthquake	189	65.6	99	34.3	–	–	–	–	288
	Total per class	Landslide	1180		746		152		67		2145
		Earthquake	1252		739		16		–		2007
	% of total	Landslide	55.01		34.77		7.08		3.12
		Earthquake	62.3		37		0.79		–

Table 8. Details of summary statistics of the risk index maps along with intermediate maps of vulnerability and hazard values.

Hazard	Maps	Summary statistics
		Minimum	Maximum	Mean	Sum	Standard deviation
Landslide	Hazard	0	4	1.76	3586	0.88
	Vulnerability	0	446	8.5	277,175	33.82
	Risk	0	1072	15.7	13,142	81.14
Earthquake	Hazard	0	0.2410	0.1009	204,804	0.042
	Vulnerability	0	466	58.4	170,476	86.02
	Risk	0	32.58	5.11	577,624	7.009

Figure 7. Multi-hazard risk map for Arithang ward (009).

Figure 8. Cross profile plot along the Arithang ward among buildings at high risk.