Subsoil and ground of Paris’s 9th arrondissement
No quarry recorded Paris 75009
The 9th arrondissement (Opéra, Pigalle, Saint-Georges) lies on the southern edge of Montmartre hill: Fontainebleau sands and green marls at depth towards the north, with a more stable alluvial terrace to the south. No quarry is officially listed by the IGC (Paris quarry inspectorate) for this arrondissement, on the edge of the 18th and 10th gypsum areas.
What public data say about the 9th
| Underground quarries recorded by the IGC (Paris quarry inspectorate) | None |
|---|---|
| Nature of the ground | Southern edge of Montmartre hill |
| Foundation issue | Ground varies depending on proximity to the hill. A G1 geotechnical study is recommended, particularly for plots close to the boundary of the 18th. |
Documented events in the 9th
22 December 1995
Subsidence on rue Papillon
Rue Papillon (9th)
Two buildings are subsiding above the RER line E worksite. The investigation concludes that geological and human problems combined.
Source: Le Nouvel Obs / Rue89 — The holes in Parisian Swiss cheese
Ground, fill and clay shrink-swell
The 9th arrondissement (Opéra, Pigalle, Saint-Georges) lies on the southern edge of Montmartre hill: Fontainebleau sands and green marls at depth towards the north, with a more stable alluvial terrace to the south. No quarry is officially listed by the IGC (Paris quarry inspectorate) for this arrondissement, on the edge of the 18th and 10th gypsum areas.
Ground varies depending on proximity to the hill. A G1 geotechnical study is recommended, particularly for plots close to the boundary of the 18th.
Unlike almost all French municipalities, inner Paris has no official mapping of the clay shrink-swell hazard (RGA). The BRGM explains this explicitly: the Paris subsoil is largely made up of reworked and artificial materials (backfill, infilled former quarries), which does not correspond to the standard methodology for this mapping — centred on detached houses, which are in the minority in Paris. This does not mean that there is no risk of differential settlement, but that no official area-by-area study exists for the capital: a ground investigation remains the only reliable way to assess a specific plot before purchase or construction.
Steps to take in the 9th before a purchase or works
- IGC (Paris quarry inspectorate) information sheet — the authoritative source on the condition of the parcel’s subsoil: €10, issued within 8 days, via the City of Paris online service.
- Statutory risk statement (ERP) — mandatory for sale and letting, generated from Errial; note, it does not return cavity data in Paris.
- geotechnical survey — G1 mission before purchasing a building plot, G2 AVP before a construction or underpinning project.
- Referral to the IGC (Paris quarry inspectorate) for planning — prefectoral orders require it to be consulted for any planning permission in a quarry-risk area.
Frequently asked questions
Are there underground quarries beneath Paris’s 9th arrondissement?
No underground quarry is listed by the IGC (Paris quarry inspectorate) for the 9th arrondissement. Areas of former quarries in inner Paris are concentrated in the south (5th, 6th, 12th, 13th, 14th, 15th, 16th, in coarse limestone) and in the north-east (10th, 18th, 19th, 20th, in gypsum). This does not mean that there are no ground-related issues at all: the 9th falls under the « ground and foundations » section.
Is a ground investigation still needed in the 9th?
Yes, whenever there is a construction, extension or underpinning project. Ground varies depending on proximity to the hill. A G1 geotechnical study is recommended, particularly for plots close to the boundary of the 18th.
Why do cavity data for the 9th not appear on Géorisques?
Because for départements 75, 78, 91, 92, 93, 94 and 95, cavity data are not published on the Géorisques portal: they can be consulted with the IGC (Paris quarry inspectorate) for Paris and the inner suburbs, or with the relevant interdepartmental service. This is why a standard statutory risk statement (ERP) remains silent on Paris quarries and gypsum.
Is quarry risk in the 9th covered by insurance?
Disorders linked to former quarries do not fall under the « natural disaster » scheme. In the event of collapse, infill works, estimated at 40 000 to 200 000 €, remain the responsibility of the owners. This is what makes checking before purchase essential.
Other arrondissements
- Subsoil of the 8th arrondissement
- Subsoil of the 10th arrondissement
- Subsoil of the 7th arrondissement
- Subsoil of the 11th arrondissement
- See the 20 arrondissements
Sources
- Wikipedia — Paris, Geology section
- City of Paris — Everything you need to know about the subsurfaces
- BRGM — Why is there no map of the clay shrink-swell hazard for Paris?
- Géorisques — Clay shrink-swell, 2026 version (data)
- Le Nouvel Obs / Rue89 — The holes in Parisian Swiss cheese
- Géorisques — Underground cavities (data)
- City of Paris — the IGC (Paris quarry inspectorate) location
- City of Paris — Known areas of former quarries (IGC)
Page updated on 11 September 2026.