Martigues: Clay Soil, Subsidence and Cracks – Official Data

The geological and climate context of Martigues

Yes, that is the hypothesis to check first: Martigues has 11 drought decrees (full list below) and 15 flood decrees, i.e. 26 Cat Nat decrees in total according to GASPAR. The local rainfall matches the classic shrink-swell scenario: two dry years back to back (2020 and 2023), then a rebound to 759 mm in 2024 – exactly the kind of alternation that puts foundations to work in the “Provençal Venice” and around the Étang de Berre.

Cassini Expertise, an independent building expert, handles drought-related cracks and damage in Martigues and more widely across the 13. This page sets out the commune’s public data: keep it handy if you need to date damage, build an insurance file or negotiate a sale.

Martigues: drought, clay and cracks – what the official data says

The GASPAR database (decrees published in the Official Gazette since 1982) lists 26 natural disaster decrees for the commune:

• 11 drought decrees (differential ground movement linked to clay shrink-swell)
  • event of 01/05/1989 (decree of 25/01/1993)
  • event of 01/01/1992 (decree of 23/02/1999)
  • event of 01/01/2006 (decree of 31/03/2008)
  • event of 01/01/2007 (decree of 07/08/2008)
  • event of 01/07/2007 (decree of 07/08/2008)
  • event of 01/01/2016 (decree of 25/07/2017)
  • event of 01/01/2017 (decree of 10/07/2018)
  • event of 01/01/2018 (decree of 16/07/2019)
  • event of 01/04/2019 (decree of 28/07/2020)
  • event of 01/04/2022 (decree of 03/04/2023)
  • event of 01/04/2023 (decree of 18/06/2024)
• 15 flood and storm decrees

What to do with it in practice: note the date your cracks appeared or worsened. If that period falls within one of the windows above and you declared the claim to your insurer within 30 days of the decree, Cat Nat compensation is a realistic prospect. If no declaration was made, or the date matches no decree, the route against the seller for hidden defect or fraudulent concealment remains – but the damage will then need to be dated by survey.

What the official clay mapping says

The GéoRisques platform (BRGM) classifies Martigues at high exposure to clay shrink-swell, with some sectors at medium exposure. This is the benchmark level your insurer and the notaire already consult to assess the risk on your plot – you can check it yourself on georisques.gouv.fr by entering your address. Another point to watch if you are buying or doing basement works: the commune is also classed as radon potential class 2 (IRSN/GéoRisques data), a building-health marker worth knowing.

This ranking is read alongside the decree history above: exposure tells you what can happen, the decrees tell you what has already happened. A house in a “high exposure” area that has come through one or more dry summers deserves regular visual checks of its cracks, even with no worrying sign today.

What characterises Martigues from a building surveying perspective

Martigues spreads across several arms of the Étang de Berre, and that waterside geography is exactly where the shrink-swell risk concentrates. Between the old quarters of Jonquières, l’Île and Ferrières, the hillside estates of the 1970s-80s and the newer developments pushing towards La Couronne and the plain, the soil alternates clayey marl, old fill and sandy-limestone ground: within a few hundred metres, two neighbouring houses can rest on completely different soils. Most of the individual houses of that era were built on shallow strip foundations, without a prior soil survey, at a time when the sensitivity of the clays around the étang was underestimated. Add the pines and cypresses planted close to bearing walls for shade and windbreak, whose roots dry the ground locally in summer, and the piers of houses built on sloping or worked ground, and you get the classic recipe for differential settlement: stair-step cracks at openings, slabs pulling away from walls, sticking doors. The subdivisions extended over former marshy areas near the étang also raise the question of poor-quality fill, which amplifies movements.

Drought in the rear-view mirror: 35 years of measured rainfall

The weather archives for the area cover 35 complete years (1991-2025). The driest ever recorded: 2017, with 372 mm over the year, against a local average of 606 mm. 2022 ranks as the 11th driest year out of 35 (502 mm against an average of 606 mm); 2023 follows in 2nd place (388 mm).

This ranking gives the true measure of the recent sequence: when the years 2020-2023 crowd into the top of the drought table, the clay has not had time to rehydrate between episodes – the classic scenario for delayed cracks. The reverse is just as instructive: a very wet year following an exceptional drought causes abrupt swelling of the ground.

Martigues: 26 Cat Nat decrees since 1982, in chronological order

Each line = an event recognised by an interministerial decree published in the Official Gazette (GASPAR database):

• 🔵 11/1982 → 11/1982 – Cyclones / Storms (decree of 18/11/1982)
• 🔵 11/1982 → 11/1982 – Floods (decree of 18/11/1982)
• 🔵 11/1982 – Floods (decree of 24/01/1983)
• 🔴 05/1989 → 12/1991 – Drought (RGA – clay shrink-swell) (decree of 25/01/1993)
• 🔴 01/1992 → 10/1998 – Drought (RGA – clay shrink-swell) (decree of 23/02/1999)
• 🔵 09/1993 → 09/1993 – Floods (decree of 08/03/1994)
• 🔵 09/1994 → 09/1994 – Floods (decree of 06/12/1994)
• 🔵 09/1998 – Floods (decree of 29/12/1998)
• 🔵 10/2002 – Floods (decree of 17/01/2003)
• 🔵 12/2003 → 12/2003 – Floods (decree of 05/02/2004)
• 🔵 09/2005 – Floods (decree of 10/10/2005)
• 🔵 11/2005 – Floods (decree of 11/04/2006)
• 🔴 01/2006 → 03/2006 – Drought (RGA – clay shrink-swell) (decree of 31/03/2008)
• 🔴 01/2007 → 03/2007 – Drought (RGA – clay shrink-swell) (decree of 07/08/2008)
• 🔴 07/2007 → 09/2007 – Drought (RGA – clay shrink-swell) (decree of 07/08/2008)
• 🔵 11/2014 – Floods (decree of 17/02/2015)
• 🔴 01/2016 → 12/2016 – Drought (RGA – clay shrink-swell) (decree of 25/07/2017)
• 🔴 01/2017 → 12/2017 – Drought (RGA – clay shrink-swell) (decree of 10/07/2018)
• 🔴 01/2018 → 03/2018 – Drought (RGA – clay shrink-swell) (decree of 16/07/2019)
• 🔵 10/2018 – Floods (decree of 24/12/2018)
• 🔴 04/2019 → 09/2019 – Drought (RGA – clay shrink-swell) (decree of 28/07/2020)
• 🔵 10/2019 → 10/2019 – Floods (decree of 30/10/2019)
• 🔵 11/2019 → 11/2019 – Floods (decree of 12/12/2019)
• 🔵 11/2020 – Floods (decree of 14/12/2020)
• 🔴 04/2022 → 09/2022 – Drought (RGA – clay shrink-swell) (decree of 03/04/2023)
• 🔴 04/2023 → 06/2023 – Drought (RGA – clay shrink-swell) (decree of 18/06/2024)

How an expert reads this: 11 droughts and 15 floods. Clusters (several decrees close together) mark crisis periods – the summer sequence of 2022-2023 is the best recent example. An owner whose damage dates from a covered period has a solid Cat Nat file; outside a covered period, the route is a claim against the seller.

Damp, water ingress and rising damp in Martigues

Damp in a wall can have four causes – rising damp, water ingress, condensation or a leak – and the treatments are completely different depending on the origin.

You have damp marks in Martigues and you are looking for a solution. Before signing anything, know this: most companies that sell treatments (resin injections, drainage) are selling a product, not a diagnosis – and they have every interest in concluding it is rising damp, even when it is not.

The four causes and how to recognise them

• Rising damp: water climbs from the ground into the walls by capillary action. Marks low on the walls, rarely above 1 to 1.5 m, often with saltpetre and blistering render.
• Water ingress: water penetrates from outside (roof, cracked façade, gutter, terrace). Localised stains, often linked to rain, not necessarily at the foot of the wall.
• Condensation: humid indoor air condenses on cold walls for lack of ventilation. Mould at cold points (corners, behind furniture), streaming windows.
• Leak: defective pipe or drain. A pinpoint stain, often near a bathroom or kitchen, sometimes revealed by unexplained excess water consumption.

The trap of the diagnosis sold by the treatment contractor

In Martigues, clay ground and the proximity of the Étang de Berre favour rising damp, but also condensation in poorly ventilated homes. A damp-treatment contractor coming to give a “free quotation” has an obvious bias: injections are what he sells. The result: rising damp gets diagnosed (and treated at great expense) when the real problem is a blocked gutter or a missing ventilation system. The treatment achieves nothing, the damp comes back, and you have paid for nothing.

Before any financial commitment, have an independent diagnosis carried out, with no commercial interest in selling a treatment. If you are in Martigues, contact us for an objective diagnosis. To go further, see our damp guide for the 06, 83 and 13, which details the diagnostic and treatment methods suited to each cause.

Why do cracks appear several months after the drought?

Annual rainfall measured on the Martigues weather grid (Open-Meteo data):

• 2019: 647 mm · 2020: 455 mm · 2021: 710 mm · 2022: 502 mm · 2023: 388 mm · 2024: 759 mm
• Average over the period: 576 mm/year, driest year: 2023 (388 mm)
• Two marked dips: 455 mm in 2020, then 388 mm in 2023
• Followed by a clear rebound in 2024, to 759 mm (+32%)

Clay shrink-swell plays out in two stages: the drought dries the clay at depth (shrinkage, first micro-cracks), then the returning rain rehydrates the ground in one go (swelling, differential settlement). If your house was built between 1970 and 2000 on shallow foundations – the most common case in the sector – watch your walls 12 to 24 months after each dry summer: that is the usual delay before cracks appear.

Which crack signs should alert me in Martigues?

• A stair-step crack, passing through the wall, open by more than 2 mm
• A crack that is moving (fit a plaster or paper tell-tale and check it after several months)
• Associated damage: doors and windows that stick, floor tiles splitting diagonally, render that bulges
• Aggravating factors on site: a house on clay ground, a tree close by, a drain that no longer does its job

With 11 drought decrees on Martigues’ record, as soon as several of these signs stack up in your home, have a survey carried out before any repair – and before any buying or selling decision. Repairing too quickly without a diagnosis masks the evidence you will need for the insurer or the court.

Buying or selling a cracked house in Martigues: what recourse do you have?

Between the recent drought decrees and the volume of transactions, quite a few properties change hands with damage passed over in silence. If you discover cracks after buying, two levers exist:

• Hidden defect (vice caché, Article 1641 of the French Civil Code): serious cracks, not visible at a viewing, predating the sale → price reduction or cancellation of the sale
• Fraudulent concealment (dol, Article 1137): the seller knew and hid the damage → cancellation plus damages, within 5 years; the commune’s GASPAR decree then strengthens your file

Before acting, gather your evidence: dates when the cracks appeared, dated photographs, works quotations – and cross-reference them with the decrees listed above. On the legal side, instruct a French property lawyer.

What actually happens during a drought/clay survey in Martigues?

• Technical visit: crack mapping and classification, width measurements, functional damage
• Context: clay zoning, the commune’s Cat Nat record (11 drought decrees), local drought episodes
• Costing of repair works: underpinning, injections, drains – with several scenarios
• A written report usable by the insurer or the lawyer

Independent expert, with no ties to any works company. Request a visit in Martigues – see also our complete guide to RGA and Cat Nat in the 06, 83 and 13.

Soil surveys on clay ground: what the regulations say

The requirement for a prior geotechnical survey has applied since 1 October 2020 (ELAN law, art. 68); the new exposure map of 1 July 2026 widens its scope. This requirement, introduced by the ELAN law no. 2018-1021, article 68 (decree no. 2019-495 of 22 May 2019), applies to Martigues (high exposure under the BRGM classification).

• What it changes for building: a soil survey is no longer optional – the ELAN law makes it compulsory in exposed zones for any sale of unbuilt land and any construction contract. Adapted foundations, ground treatment, drainage arrangements: the specifications flow directly from the survey.
• What it changes when buying a recent property: ask whether the survey was carried out and which specifications were applied. A house built without following the geotechnical recommendations on clay ground is a medium-term cracking risk.
• What it changes for sellers: the absence of a survey on a property built before the requirement is not a defect in itself – but if damage appears, a seller who knew about it and concealed it exposes themselves to a claim for fraudulent concealment (dol).
• The link with the data above: Martigues combines high exposure with a documented record of drought decrees. Building or buying here without checking the nature of the ground means building on a known and measured risk.

Cassini Expertise handles these files: compliance checks between geotechnical specifications and what was actually built, damage surveys on clay ground, second-opinion expert assessments. Request a consultation.

Frequently asked questions

Is Martigues in a clay risk zone?

Yes. The Bouches-du-Rhône is very largely covered by the clay shrink-swell hazard (BRGM mapping, consultable on georisques.gouv.fr), and in Martigues the GASPAR record with 11 recognised drought decrees confirms the risk is not theoretical – it has already materialised several times. If you are buying in this sector, systematically ask the seller for the état des risques et pollutions (ERP).

Can a cracked house in Martigues be covered under natural disaster provisions?

Only if the damage dates from a period covered by a decree (last recognised drought periods: 1993, 1999, 2008, 2017, 2018, 2019, 2020, 2023, 2024) and if the claim was declared within 30 days of the decree being published. Otherwise, the route against the seller remains – and precisely dating the damage through a survey then becomes the heart of the matter.

Can the figures on this page be verified?

Yes: the decrees come from the GASPAR database (Official Gazette, open data sets, 2025 update), the rainfall from the Open-Meteo weather archives for the Martigues grid. Cassini Expertise does not touch this data – you can cross-check it yourself before making a decision.

What is the rainfall situation? (as at 04/10/2026)

In the commune: recent rain (3 days ago). Rainfall over the last 30 days: 36 mm, against roughly 58 mm expected at this time of year – a 38% deficit.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

Weekly drought update (as at 05/10/2026)

In the commune: recent rain (4 days ago). Rainfall over the last 30 days: 37 mm, against roughly 58 mm expected at this time of year – a 36% deficit.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

What is the rainfall situation today? (as at 12/10/2026)

In the commune: recent rain (5 days ago). Rainfall over the last 30 days: 125 mm, against roughly 62 mm expected at this time of year – a surplus of 102%.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

Weekly drought update (as at 19/10/2026)

In the commune: no notable rain for 12 days. Rainfall over the last 30 days: 125 mm, against roughly 66 mm expected at this time of year – a surplus of 89%.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table visible above: it is the first signal owners can track themselves, before any cracks appear.

Water table memory: 15 years of measurements, a well-documented context

The reference piezometric station for the sector (002JHMX) has been monitoring the water table since 2012 – 15 years of records. As at 21/09/2026, the mean level over the last thirty days is 1.65 m NGF. Across the whole record, the water table has spent only 75.0% of its time below this level: a sustained level for the season.

• Last comparable episode: 03/10/2024 – 2.0 years ago
• Frequency: 69 similar episodes recorded since 2012, i.e. a return every year on average – in hydrologists’ language, an intermediate episode
• Historical minimum: 1.17 m NGF, reached on 07/04/2021

This long memory changes how the risk is read: a low level is not merely a weather episode, it is an event whose frequency is known. For a house on clay, it is that frequency that informs the probability of further settlement – and hence the urgency of precautions.

Find out more: Article 1641 of the Civil Code and the hidden defects warranty (garantie des vices cachés), explained.

Survey carried out by Frédéric Faucouneau, independent building expert – Antibes, Alpes-Maritimes (06), Var (83), Bouches-du-Rhône (13). Find out more

📅 Last updated 06/11/2026 - Cassini Expertise, independent building expert – departments 06, 83 and 13.