What March 2025 taught Bangkok's towers

Several hundred towers, ten million inhabitants, and ground whose softness geologists know well: until 28 March 2025, no one had seen Bangkok put through a real earthquake. That day, the city was tested at full scale, and the instruments were in place. Accelerometers recorded, the Department of Public Works inspected nearly 7,000 buildings in ten days, and researchers compared the ground motion with the code's design spectra. What remains is a body of evidence about its building stock that few cities possess — and what it says about the Thai property market is more precise than what most people took away from it.

What the records say first

Across the whole metropolitan area, only one building collapsed completely: the State Audit Office tower in Chatuchak — a public office building still under construction, never handed over, never occupied. CBS News, as early as 31 March 2025, described it as the only tower in Bangkok to have given way entirely; a study published in 2025 in the Bulletin of Earthquake Engineering reaches the same conclusion. No occupied residential building collapsed.

The inspections give the measure of the rest. Of 6,903 buildings examined nationwide between 28 March and 6 April 2025, 55 were barred from use, only two of them in Bangkok; of 498 public buildings surveyed by the Earthquake Research Centre of Thailand, 91.2% were undamaged. Damage was widespread; structural failures remained the exception.

What the inspections found, March-April 2025:

What happened, precisely

The earthquake occurred on the Sagaing Fault, in Myanmar, at a depth of 10 kilometres. The USGS gives a magnitude of Mw 7.7, a strike-slip mechanism and a supershear rupture of 460 to 500 kilometres, one of the longest ever observed. The epicentre lies about 1,000 kilometres from Bangkok; as the rupture propagated southwards, its closest point to the capital was about 600 kilometres away.

In Bangkok, peak ground acceleration measured at the PWSA station reached 0.019 g north-south and 0.023 g east-west: the strongest motion ever recorded in the capital, and a low acceleration in absolute terms. What mattered was not the violence of the shaking but its period and its duration.

Why does a city a thousand kilometres from the epicentre move?

Bangkok is built on a deep sedimentary basin: bedrock lies 500-2,000 metres below the surface, beneath 15 to 30 metres of soft clay with a very low shear-wave velocity. The mechanism, described by Ornthammarath and co-authors in Geoenvironmental Disasters in 2023, comes down to the contrast between these two media: the wave slows down as it enters the sediments, part of its energy becomes trapped there and is converted into surface waves, mainly Love waves. The motion is not only amplified; it lasts longer than at a nearby rock site. On 28 March 2025, amplification was measured relative to stations outside the basin — about 3 in acceleration, 4 to 5 in velocity — in two period bands: 1 to 3 seconds and 5 to 7 seconds.

These two bands are what matters to a buyer. A building resonates when its natural period of oscillation matches that of the ground. A low-rise house oscillates over a very short period: the basin does not affect it. A sixty-storey tower oscillates over about six seconds — exactly in the second amplified band. That is why, a thousand kilometres from an earthquake, it felt what a single-storey house did not. It is not an anomaly; it is physics, and Thai engineers know it.

Thailand did not discover seismic design in 2025

This is the decisive section for anyone comparing two buildings. Thailand's seismic regulations were not born of the earthquake: they have existed since 1997, have covered Bangkok since 2007, and were last tightened in 2021 — four years before.

The five successive regimes, and the one under which a building was designed:

The most telling fact fits in one sentence. According to a case study by the engineering firm Meinhardt on a 36-storey tower in Bangkok, the calculation method required in 2021 produces seismic forces at least three to four times higher than those required by the 2007 regulation.

The nuance comes from the same document and matters as much as the figure: this tower, designed under the old regulation and then reassessed during construction under the new one, met it without structural strengthening, with non-linear time-history analysis showing actual storey forces at about 70% of those predicted — a 30% margin.

Did the code pass its first real test?

Over the range that concerns the vast majority of buildings, yes. The authors of the Bulletin of Earthquake Engineering study compared the ground motion of 28 March 2025 with the design spectra of the DPT 1301/1302-61 standard. Between 1 and 3 seconds — the range of ordinary high-rise buildings — the design spectra exceeded the actual demand. The code was on the right side. Beyond 5 seconds, however, the recorded accelerations exceeded the code values. This is the range of the most slender towers, and the researchers draw a recommendation from it: incorporate 2D and 3D basin amplification effects.

What the investigation established about the Chatuchak tower

The State Audit Office tower had 33 storeys and stood 137 metres tall. The contract, awarded to a consortium of Italian-Thai Development and China Railway No.10 Engineering Group (Thailand) for THB 2.136 billion (€55.7 million), had started in 2020: the structural shell had just been completed, and the façade and building services were in progress — a building neither finished, nor handed over, nor certified for occupancy.

Ninety-five deaths had been confirmed when the search ended, on 13 May 2025; the consolidated toll after identifications stands at ninety-six. The victims were overwhelmingly construction workers on the site, many of them migrant workers. The State paid THB 129.86 million (€3.38 million) in preliminary aid and compensation.

The official State Audit Office report, published on 20 March 2026, identifies four causes:

1. The collapse began at levels 1 to 4, through shear failure of the shear walls.
2. The concrete cores taken from these walls had a strength below the specified threshold.
3. The construction drawings did not comply with regulations, resulting in a structural strength below the legal minimum.
4. The anchorage length of the reinforcement between coupling beams and shear walls was shorter than required.

All four causes are construction defects; none of them implicates Bangkok's seismicity. The question of the reinforcing steel led to divergent conclusions and is not among them.

The courts have been seized: on 7 August 2025, twenty-three individuals and entities were indicted before the Criminal Court on sixty-seven counts, including non-compliant construction causing death and offences under the Building Control Act. The proceedings are ongoing; no ruling on the merits had been handed down as of 24 September 2026.

What can be checked before buying?

At a round table of the Asia Real Estate Summit on 2 October 2025, Thai professionals summed up the change: "It is no longer just a question of location. It is a question of trust." Trust, here, is documented.

• The building permit, form Or.1 (อ.1), under section 21 of the Building Control Act: its filing date shows under which seismic regulation the project was designed.
• The certificate of occupancy, form Or.6 (อ.6), under section 32: it attests that the completed building has been inspected and may be occupied.
• The engineer's inspection certification, under section 32 bis, for buildings of 23 metres or more, or of more than 10,000 m².
• The EIA approval, mandatory before the permit. The threshold commonly cited is 80 units and/or 4,000 m², but two divergent formulations circulate: a Thai lawyer will settle it.
• The annual and five-yearly inspection reports, required by Ministerial Regulation B.E. 2548 of 2005 for buildings taller than 23 metres and condominiums of more than 2,000 m². The condominium's juristic person (building management) holds them, and failure to comply is punishable by a fine of up to THB 60,000 (€1,563), then THB 10,000 (€261) per day.
• The structural engineer's licence, with the Council of Engineers, which keeps the register of licensed engineers.

On structure, the standard system for Bangkok towers is documented: a central core of reinforced-concrete shear walls combined with perimeter frames, with performance-based design for slender buildings. A serious developer can say which one it chose, and under which regulation its permit was filed.

An honest clarification: in none of the legal sources consulted did we find a standardised "seismic compliance certificate" handed to the buyer. Compliance is carried by the permit and by the engineer's signature — so it is the permit you should ask for.

Warranty and insurance: what exists, what does not

The standard sale contract for a condominium unit must provide for a developer's warranty of five years for the structure and equipment, two years for other components — section 6/2 of the Condominium Act, mandatory public-order minimums. Under general law, section 600 of the Civil and Commercial Code makes the contractor liable for defects for five years from delivery, and section 601 requires action to be brought within one year of the defect appearing.

On the insurance side, earthquakes are covered by Thai fire policies — but with a sub-limit: THB 20,000 per year (€521) on a standard residential policy, with an optional extension available. In a condominium, the common areas fall under an Industrial All Risk policy taken out by the building management; the private unit falls under the owner's policy, and therefore under this sub-limit. The point to watch is not the cover; it is its ceiling. On 7 July 2025, the Thai General Insurance Association estimated claims at up to THB 50 billion (€1.30 billion) for around 150,000 claims filed.

What the market did next

In April 2025, Kasikorn Securities expected a 50% fall in high-rise condominium transfers over the year. The consolidated figures corrected it: according to the REIC, 2025 ended with 316,214 transfers, down 9.1%, for THB 864.913 billion (€22.54 billion). Above all, the fourth quarter marked a recovery, led by condominiums: up 8.6% in volume and 17% in value. The REIC expects 2026 to stabilise at 314,593 transfers.

The most telling point lies elsewhere: the analyses published in January and February 2026 — KKP Research, REIC, JLL, CBRE, Colliers — no longer attribute the market's weakness to the earthquake, but to household debt and credit restrictions. The market settled the question itself, in less than three quarters. This movement does not read the same way from one province to another, and we have detailed it destination by destination in our comparison of Thailand's six markets.

Who published what

Four listed developers published verifiable communications. AP Thailand inspected its 82 projects between 28 March and 3 April 2025, in two phases — in-house engineers, then four named external experts. Origin Property inspected 55 of its 83 delivered projects, Supalai its 90 projects nationwide, and Sansiri claims more than 200 projects declared safe. Eleven others reported inspections through the press.

When we model a choice between two buildings

What you can do now

Placing a building against the successive versions of the code is an exercise in dating before it is a technical one. For 7,865 projects, our database indexes the year of completion, the number of storeys and the developer: these three fields are enough to know under which regime a project was most probably designed. It is a sorting method, not an engineer's opinion — the Or.1 permit alone settles it.

Whether you are comparing two Bangkok towers or branded residences, first place them in time with the project explorer and the developer leaderboard, then ask us for the list of documents to request from the seller. For structural analysis and legal review, we refer you to an engineer licensed by the Council of Engineers and to a Thai lawyer.