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Where to read the seismic zone for a listed Indian city — IS 1893

Choose a state and a city from a curated list of 82 cities. Today every city gets a pointer to IS 1893 (Part 1):2016 Fig. 1 instead of a zone: the IS 1893 seismic zone and zone factor Z are shown only for a city whose row has been confirmed against the standard with the check recorded, with an AI-written note on what they mean for design, and no row has been yet. Seismic is the only hazard looked up: the basic wind speed is withheld until our table is verified against IS 875 (Part 3), and flood, cyclone and storm surge, liquefaction, landslide, tsunami and snow load are not assessed. The values are city-level starting points to verify for the specific site.

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The problem

Early in a project in India, the seismic zone under IS 1893 (Part 1) sets the scale of the seismic problem: it decides the zone factor Z the design starts from. Finding it means opening the code's zone map and reading off where the town falls.

Site Hazards is built for that first look. It shows a city's zone only once that city's check against IS 1893 (Part 1) is recorded; none is yet, so every seismic card says the zone is not confirmed and points to the zone map. The wind card says "not assessed": the wind table is unverified against IS 875 (Part 3), so you read the speed yourself.

How it works

Site Hazards works from a curated list of 82 cities across 33 of India's 36 states and union territories — not a complete gazetteer. It does not accept an address or coordinates.

  1. Choose the state or union territory. Andhra Pradesh, Lakshadweep, and Dadra and Nagar Haveli and Daman and Diu have no cities listed, and the tool says so.
  2. Choose a city from the list. Only listed cities can be assessed, and nothing is guessed from the nearest one.
  3. Select Assess. For a city whose check is recorded, the seismic result gives the IS 1893 (Part 1) zone and zone factor Z. For any other city — every city today — it says the zone is not confirmed, shows no zone and no Z, and points you to IS 1893 (Part 1):2016 Fig. 1. The wind card shows no number: no wind row's check is recorded.
  4. Six further hazards are listed as not assessed, each with a note on where to obtain it: flood, cyclone and storm surge, liquefaction, landslide and slope stability, tsunami, and snow load. Silence is not a finding that the site is clear.
  5. Where a value is shown, an AI-written note explains what it means for design, instructed to base everything on the values shown, to name IS 1893 without inventing clause numbers, and not to add detailing rules or name other standards. A model can ignore an instruction, so read the detailing requirements in the codes yourself. Where no value is shown, no AI note is written.

The stored table does not record which edition of IS 1893 its zones came from. A 7 October 2026 check against IS 1893 (Part 1):2016 withdrew one city's zone and could not confirm others, and its row-by-row results were not recorded, so no city's zone is shown until its own check is. The lookup is deterministic; only step 5 is written by AI.

Worked example

Illustrative input, not a real project:

  • state: Assam
  • city: Guwahati

For this input the tool returns a seismic card marked zone not confirmed, with no zone and no zone factor and a pointer to IS 1893 (Part 1):2016 Fig. 1, a wind card marked not assessed with no speed, and six further "not assessed" entries. With no value to explain, no AI note is written. An automated test runs this input through the tool's own lookup code and fails if this result changes.

What you would do next: read the zone for your site from IS 1893 (Part 1):2016 Fig. 1 and its zone factor from Table 3, taking care near a zone boundary, and read the basic wind speed yourself (IS 875 (Part 3) Annex A or the national code's map). Get the other hazards from the relevant authorities, a geotechnical investigation and IS 875 (Part 4) for snow. Then design.

What it doesn't do

  • It gives no zone yet. A zone is shown only for a city whose check is recorded, and none is, so every listed city gets a pointer to the zone map.
  • It assesses at most one hazard, not a site. The basic wind speed is withheld, and flood, cyclone and storm surge, liquefaction, landslide, tsunami and snow load are not assessed. A coastal or hillside site needs those answers from elsewhere.
  • It does not look up an address. Only the 82 listed cities can be assessed.
  • It gives one value for a whole city. Zone maps are coarse and their boundaries approximate, so a site near one may fall on either side.
  • It is not a site-specific seismic hazard assessment. Soil amplification and local site effects need investigation.
  • It does not calculate design actions. No base shear, design wind speed or wind pressure. Apply every factor IS 875 (Part 3) requires for the site, not a fixed list of three.
  • The note is AI-written. It can contain errors, including detailing rules it was told not to add. Check it against the published codes.

Standards StructBy AI holds summaries of for India

Our own plain-English summaries, covering a fraction of each standard; they are not the text of the standards, and not every tool uses every one. Our NBC summaries are based on NBC 2016, which BIS withdrew on 30 April 2026 when it established SP 7:2026, National Building Construction Standards 2026.

  • NBC 2016
  • IS 456 — Concrete
  • IS 800 — Steel
  • IS 875 — Loads
  • IS 1893 — Seismic
  • IS 1904 — Foundations
  • IS 13920 — Ductile detailing

Questions engineers ask

Can I enter a site address or coordinates?

No. Site Hazards works from a curated list of 82 major cities across 33 of India's 36 states and union territories. You choose the state or union territory and then a city from its list. Andhra Pradesh, Lakshadweep, and Dadra and Nagar Haveli and Daman and Diu have no cities listed, and a site outside a listed city cannot be assessed at all — nothing is substituted from the nearest listed city.

What does it return?

Today, for every listed city, a seismic card marked zone not confirmed, with no zone and no zone factor Z, and a pointer to where both are read in the edition in force: IS 1893 (Part 1):2016 Table 3 / Fig. 1. A zone and its zone factor Z are shown only for a listed city whose row has been confirmed against the standard with the check recorded; where it has not, the seismic card shows no zone and says so, pointing to the zone map (Fig. 1) instead. No row has been confirmed yet, so today every listed city gets that pointer. The basic wind speed is withheld: our stored wind table has not been verified against IS 875 (Part 3) — no source, edition, table or checker is recorded for any of its rows — so the wind card says "not assessed" and shows no number until each row has been checked with the standard open. Six further hazards are listed as not assessed, with where to obtain each: flood, cyclone and storm surge, liquefaction, landslide and slope stability, tsunami, and snow load. Where a value is shown, an AI-written note explains what the seismic values mean for design (where none is, no note is written), and it is instructed not to add detailing rules or name other standards. A model can ignore an instruction, so read which detailing requirements the zone triggers in the codes yourself. A reminder to verify the values for the specific site closes every result.

Where do the values come from?

From a curated table we compiled that assigns each listed city a seismic zone. The table records neither who compiled it nor which edition of IS 1893 (Part 1) it was compiled from. A 7 October 2026 check against IS 1893 (Part 1):2016 withdrew one city's zone and could not confirm others, and its row-by-row results were not recorded, so a city's zone is withheld until its own check is recorded — and none is yet. The same table holds a basic wind speed for each city, which is withheld until every row has been verified against IS 875 (Part 3) with its source, edition, table and checker recorded. It gives one value per city, and every value must be checked against the edition you are designing to.

Does it replace a site-specific seismic hazard study or a soil investigation?

No. The zone maps are coarse and a site near a boundary may fall on either side of it. Site-specific seismic hazard, soil amplification and local wind effects need investigation, and the figures here are a starting point for design, not a substitute for that work.

Is the basic wind speed the design wind speed?

The tool currently gives no basic wind speed at all — the value is withheld until its table is verified — and it never works out the design wind speed. Read the basic wind speed Vb for your site from IS 875 (Part 3):2015 (as amended) Annex A if your town is listed there, and otherwise from the National Building Code's basic wind speed map, now in SP 7:2026 Part C, Section 1; then apply every factor IS 875 (Part 3) requires for your site and building — treat no short list of factors, from us or anywhere else, as the complete set.

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StructBy AI outputs are automated or AI-assisted and must be reviewed by a qualified engineer before anyone relies on them. They are not professional engineering, legal or regulatory advice, and they do not replace a site-specific hazard assessment, a geotechnical investigation or a registered engineer. References to NBC 2016 and the IS codes are summaries and pointers, not the text of those documents, so verify every value and clause against the current NBC and BIS publications before you use it in design or documentation.