Seismic risk assessment for the North Eastern Region of India by integrating seismic hazard and social vulnerability

Figures & data

Figure 1. Demographic profile of the study area.

Figure 2. a) Seismotectonic map of the study area. b) Seismic source zonation of the study area showing the spatial distribution of declusterd earthquake.

Table 1. Relation between different magnitude scales.

Scale	Data points	Relation		R^2
mb to Mw	349	Mw = (1.008 ± 0.018) mb – (0.095 ± 0.086)	2.4 ≤ mb≤ 6.9	0.896
ML to Mw	277	Mw = (0.919 ± 0.022) ML + (0.286 ± 0.085)	2.5 ≤ ML ≤7.0	0.864
MS to Mw	130	Mw = (0.715 ± 0.031) MS + (1.796 ± 0.151)	3.0 ≤ MS ≤ 7.2	0.803

Figure 3. Comparison of GMPEs with the observed PGA values for a different combination of moment magnitude and hypocentral distance (km): (a) Mw 5.0, h 43, (b) Mw 5.9, h 15, (c) Mw 6.0, h 17, (d) Mw 6.0, h 34, (e) Mw 7.3, h 90.

Table 2. List of selected GMPEs.

Sl. No.	GMPE	Abbreviation	Remark
1	Jain et al., 2000 non-subduction zone: $ln(PGA)=-3.443+0.706M-0.8028ln(R)$ with SE = 0.44 subduction zone: $ln(PGA)=-0.332+0.00233R+0.59ln(R)$ with SE = 0.59 Where PGA in g, R is the shortest source-to-site distance, and SE is the standard error	JAIN2000	For Central-Himalayan region
2	Atkinson & Boore, 2003$logY=c_1+c_{2}M+c_{3}h+c_{4}R-g\cdot logR+s_l(c_5{S}_C+c_6{S}_D+c_7{S}_E)$Where Y in cm/s^2,$R=\sqrt{D_{fault}^2+{\mathrm{\Delta }}^2}$, $\mathrm{\Delta }=0.00724\times {10}^{(0.507M)}$, c1 = 2.991, c2 = 0.03525, c3 = 0.00759, c4 = −0.00206, g = 10^(1.2−0.18M), σ1 = 0.20 (intra-event) and σ2 = 0.11 (inter-event) for interface events (h < 50 km) and c1 = −0.04713, c2 = 0.6909, c3 = 0.01130, c4 = −0.00202, g = 10^(0.301−0.01M), σ1 = 0.23 and σ2 = 0.14 for in-slab events (h > 50 km) and (c5,c6,c7) = (0.19, 0.24, 0.29) for all events. $s_l$ is frequency-dependent constant. SC,SD, and SE are equal to zero for site class B (NEHRP), VS,30 > 760 m/s.	ATBO2003
3	Nath et al., 2012$ln(P)=9.143+0.247M-0.014(10-M{)}^3-2.67ln(r_{rup}+32.9458e^{(0.0663M)})$where P = PGA (g), $r_{rup}$= fault-rupture distance (km). Standard Deviation = 0.330.	NATH200	For the Shillong region of NE India
4	Anbazhagan et al., 2013$log(y)=-1.283+0.544M+b\cdot log(X+e^{(0.381M)})+\sigma$where Y = Spectral acceleration (SA) (g), $X=\sqrt{R^2+h^2}$, where R = epicentral distance (km), h = focal depth (km), b is decay parameter (−1.792), and σ = 0.283 (for 0 s period).	ANBA2013	For Himalayan region
5	Ramkrishnan et al.,2021$logy=-2.135+0.437M-1.099log(X+e^{(-0.080M)})\pm 0.549$where y = PGA (g), X = hypocentral distance (km), and SE = ±0.549	RAMK2021	For Central-Himalayan region
6	Bahuguna & Sil, 2020$ln(PGA)=6.680+1.134M-0.001R-0.7098lnR$where PGA in g, R = hypocentral distance (km) (ranges from 100–400 km), and standard deviation = 0.53	BAHU2020	For Assam region

Table 3. List of common social vulnerability indicators and their variables.

Sl. No.	Indicator	Variables
1	Population composition	P01	Population density
2		P02	Rural population (%)
3		P03	Female population (%)
4		P04	Population belongs to the socially backward class (%)
6	Age	Age01	Age less than 07 (%)
7		Age02	Age group of 07 to 60 (%)
8		Age03	Above the age of 60 (%)
9	Literacy	L01	Effective literacy rate
10		L02	Illiterate (%)
11		L03	Illiterate female (%)
12	Employment status and occupation	EO01	Population belongs to MW^1 class (%)
13		EO02	Female population belongs to MW^1 class (%)
14		EO03	Population belongs to the OMW^2 class (%)
15		EO04	Female population belongs to the OMW^2 class (%)
16		EO05	Population belongs to MrW^3 class (%)
17		EO06	Female population belongs to MrW^3 class (%)
18		EO07	Population belongs to the OMrW^4 class (%)
19		EO08	Female population belongs to the OMrW^4 class (%)
20		EO09	Non-permanent employment (%)
21		EO10	Female population with non-permanent employment (%)
22		EO11	Non-working population (%)
23		EO12	Non-working female population (%)
24	Building material	BM01	With brick or stone roof (%)
25		BM02	With kutcha roof (%)
26		BM03	With kutcha wall (%)
27		BM04	With kutcha floor (%)
28	House condition	HC01	Residential houses in dilapidated condition (%)
29		HC02	Residential cum other houses in dilapidated condition (%)
30	Family size	HH01	Houses with 4-5 households (%)
31		HH02	Houses with 6 or more households (%)
32	Amenities	A01	Houses with no electricity and have dependence upon kerosene or other oil as a source of light (%)
33		A02	Houses with no water source within or near the premises of the house (%)

¹MW: Main Workers; Workers who worked for more than six months in the reference period

OW: Other Workers; Workers other than cultivators, agricultural laborers, or household workers. e.g. Government servants, municipal employees, teachers, bankers, trade, commerce, etc.

²OMW: Other Main Workers; Main workers falling under OW

³MrW: Marginal Workers; Workers who worked for less than six months

⁴OMrW: Other Marginal Workers; Marginal workers falling under OW

Table 4. Selected variables based on PCA.

Factor	Extracted variables	Eigenvalue	Variance explained (%)	Weightage factor (wi)
1	HC01, A01, L02, P02, L03, Age01, HC02, BM03, EO12, HH02, EO11, BM02, and A02	19.528	37.87	0.42
2	BM01, EO03, EO07, HH01, Age03, and P04	2.080	27.35	0.30
3	EO02, EO06, EO05, EO10, and EO01	1.026	25.31	0.28

Figure 4. Seismic hazard curves (Shillong city).

Figure 5. Scree plot.

Figure 6. Risk matrix.

Figure 7. Spatial distribution of PGA at the bedrock level for a return period of (a) 475 years, (b) 950 years, and (c) 2475 years.

Table 5. Comparison of the estimated seismic parameters with previously reported values.

Parameter	Das et al., 2016	NDMA, 2010	Thingbaizam et al., 2008	Sharma & Malik, 2006	Bahuguna & Sil, 2020	Present study
a	1.68–5.76	-	4.47–8.59	-	0.15–4.52	3.67–4.89
b	0.43–1.07	0.66 ± 0.03–0.80 ± 0.02	0.61–1.36	0.42–1.04	0.18–0.9	0.77–1.02
Mc	3.6–4.6	-	4.0–4.8	-	-	3.4–3.7

Table 6. Comparison of estimated PGA values obtained for important cities with previously reported values.

Sl. No.	City	PGA (g)
		Present Study^‡	NDMA, 2010 ^†	Nath & Thingbaijam, 2012 ^‡	Other studies
1	Guwahati	0.60–0.85	0.23–0.40	0.66–1.40	0.35 (Ghione et al., 2021) ^⁎; 0.46–0.92 (Bahuguna & Sil, 2020) ^†
2	Agartala	0.32–0.47	0.12–0.20	0.25–0.60	0.22 (Das et al., 2016) ^⁎; 0.11–0.20 (Sil et al., 2013) ^‡
3	Aizawl	0.20–0.32	0.22–0.45	0.45–1.20	0.3 (Sharma & Malik, 2006) ^⁎; 0.1–0.17 (Sil et al., 2013) ^‡
4	Imphal	0.28–0.42	0.30–0.55	0.70–1.40	0.4 (Sharma & Malik, 2006) ^⁎; 0.18–0.8 (Pallav et al., 2012) ^‡
5	Shillong	0.61–0.83	0.25–0.45	0.72–1.30	0.55 (Ghione et al., 2021) ^⁎
6	Itanagar	0.55–0.88	0.28–0.45	0.70–1.20	0.44 (Sharma & Malik, 2006) *; 0.18 (Das et al., 2016) *
7	Kohima	0.25–0.40	0.25–0.55	0.60–1.30	0.5 (Sharma and Malik, 2006)*; 0.15 (Das et al., 2016) *

For return period of * 475 years; ‡ 475–2475 years; † 475–4950 years

Figure 8. Spatial distribution of social factors (a) Factor 1, (b) Factor 2, (c) Factor 3 and (d) SVI.

Table 7. Classification scheme of SHI, SVI, and Risk zone at a regional scale and corresponding areal distribution.

Value Range	Class	Area (%)
SHI
0.14–0.25	Very Low	18.31
0.26–0.36	Low	14.82
0.37–0.48	Moderate	7.75
0.49–0.59	High	20.48
0.60–0.70	Very High	38.64
SVI
0–0.013	Very Low	27.69
0.013–0.056	Low	20.50
0.056–0.165	Moderate	17.96
0.165–0.399	High	14.56
0.399–1.000	Very High	19.29
Risk Zone
01–02	Very Low	9.36
03–06	Low	40.40
07–10	Moderate	16.12
11–16	High	17.62
17–25	Very High	16.50

Figure 9. Spatial cluster analysis of SVI.

Figure 10. (a) Seismic hazard class; (b) Risk zonation.

Figure 11. Comparison of areal distribution (%) of different classes of SV, SH, and Risk indexes in NER.

Figure 12. Seismic hazard classification map at sub-regional level.

Figure 13. Comparison of areal distribution (%) of different seismic hazard classes at the sub-regional level.

Figure 14. Distribution of SVI classes at the sub-regional level.

Figure 15. Comparison of areal distribution (%) of different SVI classes at the sub-regional level.

Figure 16. Risk zonation map at the sub-regional level.

Figure 17. Comparison of areal distribution (%) of different risk classes at the sub-regional level.

Table 8. Classification scheme of SHI, SVI, and Risk zone and corresponding areal distribution.

		SHI		SVI		Risk Zone
State	Class	Value Range	Area (%)	Value Range	Area (%)	Value Range	Area (%)
Arunachal Pradesh	Very Low	0.334–0.405	1.61	0–0.196	27.23	1.0–2.0	0.00
	Low	0.406–0.477	3.08	0.196–0.407	15.42	3.0–6.0	34.40
	Moderate	0.478–0.549	17.59	0.407–0.701	34.32	7.0–10.0	16.52
	High	0.550–0.621	26.58	0.701–0.949	10.34	11.0–16.0	33.97
	Very High	0.622–0.692	51.15	0.949–1	12.69	17.0–25.0	15.11
Assam	Very Low	0.292–0.368	14.00	0–0.258	16.57	1.0–2.0	5.09
	Low	0.369–0.444	16.45	0.258–0.364	24.73	3.0–6.0	35.85
	Moderate	0.445–0.520	18.01	0.364–0.521	11.97	7.0–10.0	23.52
	High	0.521–0.596	18.65	0.521–0.709	34.51	11.0–16.0	22.22
	Very High	0.597–0.671	32.89	0.709–1	12.21	17.0–25.0	13.31
Manipur	Very Low	0.172–0.198	26.96	0–0.027	18.80	1.0–2.0	0.00
	Low	0.199–0.224	28.11	0.027–0.121	19.96	3.0–6.0	60.48
	Moderate	0.225–0.250	21.48	0.121–0.141	21.14	7.0–10.0	21.47
	High	0.251–0.277	13.08	0.141–0.200	29.89	11.0–16.0	17.34
	Very High	0.278–0.308	10.37	0.200–1	10.22	17.0–25.0	0.71
Meghalaya	Very low	0.500–0.536	3.67	0–0.001	8.22	1.0–2.0	0.00
	Low	0.537–0.573	9.68	0.001–0.545	23.36	3.0–6.0	17.95
	Moderate	0.574–0.609	9.50	0.545–0.788	36.39	7.0–10.0	32.23
	High	0.610–0.645	12.01	0.788–0.886	16.90	11.0–16.0	32.19
	Very High	0.646–0.682	65.14	0.886–1	15.13	17.0–25.0	17.62
Mizoram	Very Low	0.144–0.175	36.95	0–0.133	6.43	1.0–2.0	9.86
	Low	0.176–0.207	27.52	0.133–0.490	37.05	3.0–6.0	50.64
	Moderate	0.208–0.238	15.82	0.490–0.639	9.35	7.0–10.0	26.09
	High	0.239–0.270	11.96	0.639–0.854	30.83	11.0–16.0	7.90
	Very High	0.271–0.300	7.75	0.854–1	16.34	17.0–25.0	5.50
Nagaland	Very Low	0.203–0.224	19.03	0–0.027	11.51	1.0–2.0	13.18
	Low	0.225–0.245	21.12	0.027–0.074	9.48	3.0–6.0	18.51
	Moderate	0.246–0.266	23.11	0.074–0.086	9.80	7.0–10.0	16.83
	High	0.267–0.287	23.18	0.086–0.407	45.97	11.0–16.0	27.64
	Very High	0.288–0.308	13.56	0.407–1	23.25	17.0–25.0	23.83
Tripura	Very Low	0.222–0.248	13.22	0–0.309	21.20	1.0–2.0	26.64
	Low	0.249–0.273	23.88	0.309–0.310	12.98	3.0–6.0	26.84
	Moderate	0.274–0.299	23.24	0.310–0.311	17.53	7.0–10.0	9.02
	High	0.300–0.325	22.73	0.311–0.944	28.62	11.0–16.0	30.73
	Very High	0.326–0.351	16.93	0.944–1	19.67	17.0–25.0	6.78

Figure 18. Conversion from (a) m_b to Mw, (b) M_L to Mw, and (c) M_S to Mw.

Figure 19. Completeness of the earthquake catalog with time.

Table A1. Seismic parameters and M_C values.

Source zones	MC (using MAXC)	Seismic parameters		R^2
		a	b
1	3.60	4.06 ± 0.36	0.84 ± 0.07	0.96
2	3.50	3.67 ± 0.36	0.77 ± 0.07	0.95
3	3.40	4.23 ± 0.33	0.85 ± 0.06	0.97
4	3.50	4.70 ± 0.19	0.86 ± 0.03	0.98
5	3.70	4.90 ± 0.37	1.02 ± 0.07	0.97

Figure 20. Gutenberg-Richter relation for each source zone (a) Zone 1, (b) Zone 2, (c) Zone 3, (d) Zone 4, and (e) Zone 5.

Table A2. Seismic source zone characterization of the study area.

Source zones	Fault name	Fault ID	αi	χi	Observed Mmax	Calculated Mmax
						IVM	KS89
1	Main Central Thrust (MCT)	1	0.49	0.59	6.8	7.3	6.86
	Main Boundary Thrust (MBT)	2	0.51	0.41	6.8	7.3	6.86
2	Siang Fault (SiF)	3	0.18	0.16	6.6	7.1	6.63
	Lohit Thrust (LT)	4	0.20	0.40	6.3	6.8	6.32
	Mishmi Thrust (MT)	5	0.62	0.43	7	7.5	7.06
3	Shan-Sagaing Fault (SSF)	6	1.00	1.00	7.6	8.1	7.96
4	Eastern boundary thrust and Kabaw Fault (EBT & KBF)	7	0.42	0.71	7.3	7.8	7.49
	Chaurachandpur-Mao Fault (CMF)	8	0.09	0.15	7.2	7.7	7.35
	Naga Thrust (NT)	9	0.25	0.06	7.3	7.8	7.49
	Disang Thrust (DT)	10	0.24	0.08	7	7.5	7.10
5	Tista Fault (TF)	11	0.15	0.02	4.5	5	4.50
	Dhubri Fault (DF)	12	0.09	0.07	6.7	7.2	6.87
	Dhansiri-Kopili Fault (DKF)	13	0.08	0.11	5.7	6.2	5.72
	Samin Fault (SF)	14	0.05	0.13	7.1	7.6	7.64
	Oldham Fault (OF)	15	0.07	0.13	8.1	8.6	8.55
	Dhudhnoi Fault (DhF)	16	0.06	0.11	8.1	8.6	8.54
	Barapani Shear Zone (BSZ)	17	0.03	0.06	5.2	5.7	5.20
	Dauki Fault (DaF)	18	0.18	0.13	7.1	7.6	7.64
	Madhupur Blind Fault (MBF)	19	0.04	0.03	7.1	7.6	7.64
	Sylhet Fault (ShF)	20	0.09	0.11	6.5	7	6.60
	Arakan Trench (AT)	21	0.14	0.09	6.8	7.3	7.01

Figure 21. Fault level recurrence relation for source (a) Zone 1, (b) Zone 2, (c) Zone 3, (d) Zone 4, and (e) Zone.

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