Home → Learn → Seismic Zones IS 1893

IS 1893:2016 · Earthquake Engineering

Seismic Zones of India — IS 1893 Complete Guide with 3 Examples & GATE MCQs

⏱ 20 min read📅 June 2026✅ IS 1893 Part 1:2016🎓 GATE relevant

India sits on the Indian tectonic plate, which is pushing into the Eurasian plate at about 5 cm per year — making the Himalayan belt one of the most seismically active regions on Earth. IS 1893:2016 (Part 1) divides India into four seismic zones (II, III, IV, V) based on the expected earthquake intensity and assigns each zone a zone factor (Z). This guide covers the complete seismic design framework — from zone identification to base shear calculation — with three worked examples and 10 GATE MCQs.

1. Introduction

India was originally divided into five seismic zones (I to V). The 2002 revision of IS 1893 merged Zones I and II into a single Zone II, leaving four zones. Zone V (most severe) covers the entire northeast India, parts of Jammu & Kashmir, Himachal Pradesh, Uttarakhand, and the Kutch region of Gujarat. Zone II (least severe) covers the central Indian peninsula, considered relatively stable.

Every building in India must be designed for the seismic forces corresponding to its zone. IS 1893 provides the method to calculate the design seismic base shear — the total horizontal force that the building must resist during an earthquake. This force depends on the zone factor, soil type, building flexibility (time period), structural system (ductility), and building importance.

2. Concept and Theory

How earthquakes affect buildings

During an earthquake, the ground moves horizontally. The building base moves with the ground, but the upper floors lag behind due to inertia — creating horizontal forces proportional to the floor masses. A taller, heavier, more flexible building experiences larger forces. The total force at the base is called the seismic base shear (V_B).

The equivalent static method

IS 1893 allows regular, low-to-medium-rise buildings to be designed using the equivalent static method — where the earthquake is represented as a set of static horizontal forces at each floor level, proportional to the floor mass and height. This is simpler than dynamic analysis and sufficient for most Indian buildings up to about 15 storeys (or 50m height) in regular configurations.

What determines the design force?

The seismic design coefficient A_h depends on four factors: the zone factor Z (seismicity of location), the importance factor I (criticality of the building), the response reduction factor R (ductility of the structural system), and the spectral acceleration S_a/g (depends on the building's natural time period and soil type). The formula A_h = (Z/2) × (I/R) × (S_a/g) captures the combined effect of all these factors.

3. IS Code Background

Clause	Subject	Plain English
Table 2	Zone factors	Zone II: 0.10, Zone III: 0.16, Zone IV: 0.24, Zone V: 0.36
Table 8	Importance factor I	Residential/commercial: 1.0. Schools/hospitals/assembly: 1.5. Critical infrastructure: 1.5
Table 9	Response reduction factor R	OMRF: 3.0, SMRF: 5.0, SMRF with shear walls: 5.0, Braced frame: 4.0
Cl 6.4	Design spectrum	Sa/g vs T curves for three soil types (I: rock, II: medium, III: soft). Different spectral shapes for each.
Cl 7.6	Base shear	V_B = A_h × W, where W = seismic weight of the building.
Cl 7.7	Vertical distribution	Q_i = V_B × W_ih_i² / Σ(W_jh_j²). Force at each floor proportional to mass × height².

4. Key Formulas

Design Horizontal Seismic Coefficient

A_h = (Z/2) × (I/R) × (S_a/g)

Z = zone factor (0.10 to 0.36)
I = importance factor (1.0 or 1.5)
R = response reduction factor (3 to 5)
S_a/g = spectral acceleration coefficient (from design spectrum, depends on T and soil type)

Fundamental Natural Period

For RC frame: T = 0.075 × h^0.75
For RC frame with shear walls: T = 0.075 × h^0.75 / √A_w
For steel frame: T = 0.085 × h^0.75
For masonry/other: T = 0.09 × h / √d

h = height of building (m), d = base dimension in direction of vibration

Seismic Base Shear

V_B = A_h × W

W = seismic weight of building = full DL + 25–50% of LL (depending on LL intensity)
For LL ≤ 3 kN/m²: include 25% of LL
For LL > 3 kN/m²: include 50% of LL
Roof LL is not included in seismic weight

Vertical Distribution of Base Shear

Q_i = V_B × (W_i × h_i²) / Σ(W_j × h_j²)

Q_i = lateral force at floor i
W_i = seismic weight at floor i
h_i = height of floor i from base
Force increases with height² — upper floors carry more force

5. Seismic Zone Tables

Zone Factors and Cities

Zone	Z	Intensity (MSK)	Major Cities
V (Very Severe)	0.36	IX+	Guwahati, Srinagar, parts of Himachal, Kutch (Bhuj), North Bihar
IV (Severe)	0.24	VIII	Delhi, Patna, Jammu, Shimla, Dehradun, parts of Punjab
III (Moderate)	0.16	VII	Mumbai, Kolkata, Jaipur, Lucknow, Bhopal, Ahmedabad
II (Low)	0.10	VI	Chennai, Bangalore, Hyderabad, Nagpur, Thiruvananthapuram

Spectral Acceleration S_a/g (for 5% damping)

Period Range	Soil Type I (Rock)	Soil Type II (Medium)	Soil Type III (Soft)
T < 0.10s	1 + 15T	1 + 15T	1 + 15T
0.10 ≤ T ≤ 0.40s (Type I)	2.50	—	—
0.10 ≤ T ≤ 0.55s (Type II)	—	2.50	—
0.10 ≤ T ≤ 0.67s (Type III)	—	—	2.50
T > plateau	1.00/T	1.36/T	1.67/T

6. Step-by-Step Base Shear Calculation

Identify seismic zone from IS 1893 map → get Z.
Determine importance factor I from Table 8.
Determine R based on structural system from Table 9.
Calculate fundamental period T = 0.075h^0.75 (RC frame).
Identify soil type (I, II, or III) from geotechnical report.
Read S_a/g from the design spectrum for your T and soil type.
Calculate A_h = (Z/2)(I/R)(S_a/g).
Calculate seismic weight W = full DL + % of LL at each floor.
Base shear V_B = A_h × W.
Distribute V_B to each floor using Q_i = V_B × W_ih_i²/Σ(W_jh_j²).

7. Worked Examples

Example 1 — Base Shear for a G+3 Residential Building in Delhi (Beginner)

RC SMRF, Zone IV (Z=0.24). Height = 13m. Soil Type II. I = 1.0, R = 5.0. Seismic weight W = 5000 kN.

Step 1 — Natural Period

T = 0.075 × 13^0.75 = 0.075 × 7.09 = 0.532s

Step 2 — Sa/g

Soil Type II, T = 0.532s (within plateau 0.10–0.55s) → S_a/g = 2.50

Step 3 — Ah

A_h = (0.24/2) × (1.0/5.0) × 2.50 = 0.12 × 0.20 × 2.50 = 0.06

Step 4 — Base Shear

V_B = 0.06 × 5000 = 300 kN

Example 2 — Hospital in Guwahati, Zone V (Intermediate)

RC SMRF with shear walls. Zone V (Z=0.36). Height = 20m. Soil Type III. I = 1.5 (hospital), R = 5.0. W = 12000 kN.

Step 1 — Period

T = 0.075 × 20^0.75 = 0.075 × 9.46 = 0.71s

Step 2 — Sa/g

Soil Type III, T = 0.71s > 0.67s → descending branch: S_a/g = 1.67/0.71 = 2.35

Step 3 — Ah

A_h = (0.36/2) × (1.5/5.0) × 2.35 = 0.18 × 0.30 × 2.35 = 0.127

Step 4 — Base Shear

V_B = 0.127 × 12000 = 1524 kN
This is a very significant force — about 12.7% of the building weight acting horizontally!

Example 3 — Floor-Wise Distribution (Advanced)

A 3-storey building with V_B = 300 kN. Floor weights: W₁ = 1800 kN at h₁ = 3m, W₂ = 1700 kN at h₂ = 6m, W₃ = 1500 kN at h₃ = 9m.

ΣWihi²

1800×9 + 1700×36 + 1500×81 = 16200 + 61200 + 121500 = 198,900

Floor Forces

Q₁ = 300 × 16200/198900 = 24.4 kN (8.1%)
Q₂ = 300 × 61200/198900 = 92.3 kN (30.8%)
Q₃ = 300 × 121500/198900 = 183.3 kN (61.1%)
Top floor carries 61% of the base shear — this is why upper storeys experience the most damage!

8. GATE MCQs

Q1. The zone factor for Seismic Zone IV as per IS 1893:2016 is:

(a) 0.10
(b) 0.16
(c) 0.24
(d) 0.36

Answer: (c)
Zone II=0.10, III=0.16, IV=0.24, V=0.36. Memorise these four values.

Q2. Delhi falls in seismic zone:

(a) II
(b) III
(c) IV
(d) V

Answer: (c)
Delhi is in Zone IV (Z=0.24). Major earthquake risk due to proximity to the Himalayan fault system.

Q3. The response reduction factor R for a Special Moment Resisting Frame (SMRF) is:

(a) 3.0
(b) 4.0
(c) 5.0
(d) 1.5

Answer: (c)
SMRF: R=5.0 (ductile detailing per IS 13920). OMRF: R=3.0. Higher R means the structure can absorb more energy through ductility → lower design force.

Q4. The formula for design horizontal seismic coefficient is:

(a) Ah = Z × I × R × Sa/g
(b) Ah = (Z/2) × (I/R) × (Sa/g)
(c) Ah = Z × I / (2R)
(d) Ah = Z × Sa/g

Answer: (b)
A_h = (Z/2)(I/R)(S_a/g). The Z/2 converts the MCE level zone factor to DBE (Design Basis Earthquake) level.

Q5. The importance factor for a hospital building as per IS 1893 is:

(a) 1.0
(b) 1.2
(c) 1.5
(d) 2.0

Answer: (c)
Hospitals, schools, emergency buildings: I = 1.5. Normal buildings: I = 1.0.

Q6. The natural period of an RC frame building with height 16m is approximately:

(a) 0.60s
(b) 0.45s
(c) 0.32s
(d) 0.75s

Answer: (a)
T = 0.075 × 16^0.75 = 0.075 × 8.0 = 0.60s.

Q7. In the vertical distribution of base shear, the force at a floor is proportional to:

(a) W_i × h_i
(b) W_i × h_i²
(c) h_i² only
(d) W_i only

Answer: (b)
Q_i ∝ W_ih_i². The h² term means upper floors get disproportionately more force.

Q8. How much live load is included in seismic weight for LL = 2 kN/m²?

(a) 0%
(b) 25%
(c) 50%
(d) 100%

Answer: (b)
For LL ≤ 3 kN/m²: include 25%. For LL > 3 kN/m²: include 50%. Roof LL is excluded.

Q9. The Z/2 in the Ah formula converts:

(a) Peak acceleration to average
(b) MCE (Maximum Considered Earthquake) to DBE (Design Basis Earthquake)
(c) m/s² to g
(d) Static to dynamic

Answer: (b)
Z represents MCE level ground acceleration. Dividing by 2 gives the DBE level — the design earthquake with ~10% probability of exceedance in 50 years.

Q10. Chennai falls in seismic zone:

(a) II
(b) III
(c) IV
(d) V

Answer: (b)
Chennai was upgraded from Zone II to Zone III after the 2004 tsunami and subsequent seismic reassessment.

9. Common Mistakes

Mistake 1: Using Zone I. Zone I no longer exists. IS 1893:2002 merged Zones I and II. The lowest zone is now Zone II (Z=0.10).

Mistake 2: Forgetting the Z/2 factor. Students often use Z directly in Ah. The code specifies Z/2 because Z represents MCE, and we design for DBE = MCE/2.

Mistake 3: Using R=5 for OMRF. OMRF (ordinary frame without ductile detailing) has R=3.0 only. R=5.0 is for SMRF with IS 13920 ductile detailing. Using R=5 for OMRF dangerously underestimates the design force.

Mistake 4: Including 100% live load in seismic weight. Only 25% (for LL ≤ 3 kN/m²) or 50% (for LL > 3 kN/m²) is included. Roof LL is excluded entirely.

10. Quick Revision Summary

Memorise:

Zone factors: II=0.10, III=0.16, IV=0.24, V=0.36
A_h = (Z/2)(I/R)(S_a/g)
V_B = A_h × W
T (RC frame) = 0.075h^0.75
I: 1.0 (normal), 1.5 (important)
R: 3.0 (OMRF), 5.0 (SMRF)
Seismic weight: full DL + 25% LL (≤3) or 50% LL (>3)
Floor force ∝ W_ih_i² — upper floors get more
Delhi = Zone IV, Mumbai = Zone III, Guwahati = Zone V, Chennai = Zone III

Apply seismic loads automatically

StructLearn Pro calculates seismic base shear per IS 1893 and distributes forces to every floor — with correct Z, I, R, and spectral values for your city.

Start Designing Free →