Glossary
Seismic Zone
Plain-Language Definition
A geographic area classified by expected earthquake ground motion intensity, used to determine structural design requirements. Higher zone numbers indicate greater seismic hazard and more stringent structural design requirements.
Technical Context
BNBC 2020 divides Bangladesh into 4 seismic zones: Zone I (Z=0.12, lowest risk — Khulna), Zone II (Z=0.20, moderate — Dhaka), Zone III (Z=0.28, higher — Mymensingh), Zone IV (Z=0.36, highest — Sylhet). The zone factor Z is used to calculate base shear. IBC and ASCE 7 use spectral acceleration maps rather than discrete zones.
Why It Matters
Seismic zone determines the minimum earthquake resistance a building must provide. Dhaka is in Zone II (Z=0.20) — not the lowest risk zone. Buildings designed before BNBC 2020 may have been designed to lower seismic requirements. Any building acquisition in Bangladesh should verify which seismic zone and code version was used for structural design.
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