What Can a Distant Earthquake Teach Us About Urban Risk?

The March 2025 Mandalay earthquake struck over 600 km from Bangkok yet still caused insured losses in the city. Why? Because distant quakes can interact with local soil and buildings in unexpected ways. As cities grow and high-rises multiply, understanding these effects becomes critical. In this Quick Read, we highlight key insights from our latest research.

1. What did the 2025 Mandalay earthquake reveal?

On March 28, 2025, a magnitude 7.6  earthquake struck near Mandalay, Myanmar. Although approximately over 650 kilometers from Bangkok, the Thai capital experienced unexpected and damaging shaking – especially in high-rise buildings. The cause wasn’t local seismicity, and while directivity and rupture velocity played a secondary role, the main culprit was seismic wave amplification through the soft deltaic soils beneath the city.

Distant Historical Seismicity & Susceptibility to Amplified Ground Motion

Figure 1: Bangkok (red dot at the center of each sub figure) emerges as a city with high-rise buildings which is exposed to large distant earthquakes (Mw ≥ 7.5) within 300–1000 km (left) and is located on soft soils that amplify ground motion at a 1s period (right). Source: PartnerRe, using external datasets.[1]

[1] International Seismological Centre (2025), On-line Bulletin, https://doi.org/10.31905/D808B830Searches

2. Why are local soil conditions critical?

Seismic waves carry both potential and kinetic energy. When seismic waves propagate from a hard (deep rock) to a looser medium (soft sediments), the waves slow down and kinetic energy is reduced. To conserve energy, potential energy increases, causing the amplitude of the seismic waves to become larger.

3. Why can distant earthquakes still cause serious damage?

The phenomenon of distant earthquakes causing severe damage is well-documented. One of the most infamous examples is the 1985 Mexico City earthquake, where destructive shaking occurred more than 350 kilometers from the rupture zone.

This occurs when seismic waves, composed of different frequencies, are amplified depending on the depth, properties of the shallow soil and the shape of a basin they occupy. In cities like Bangkok, long-period waves are amplified, which resonate with tall buildings, increasing shaking. The result: even far-off quakes can pose serious risks to urban areas built on soft ground.

4. What are the implications for earthquake risk assessment?

Distant earthquake risk can be overlooked in assessments, leading to underestimated exposure and missed mitigation opportunities. Cities with low local seismicity may still be vulnerable due to their geology and building profiles. To better capture this risk, three factors need to be considered:

1. Soil Amplification: Soft soils can significantly amplify ground motion for tall buildings.
2. Distant Seismicity: Cities exposed to large, distant earthquakes (i.e., >300 km away) may still experience damaging shaking.
3. Exposure Characteristics: Cities with a high concentration of high-rise buildings are particularly susceptible to long-period seismic waves amplified by soft soil basins.

As cities grow vertically and expand across soft ground, it becomes increasingly important to look beyond fault lines and consider the broader geological and tectonic context. Recognizing and quantifying distant earthquake risk – especially in cities with seemingly low local seismicity – enables more accurate underwriting and portfolio management. At PartnerRe, we’ve identified additional cities where exposure concentrations may appear benign but are in fact vulnerable due to soil conditions and building profiles.

Contact us

If you would like more information about what other cities may be at risk and to discuss potential impacts to your portfolio, please reach out to us.

Contributors

Graciela Rojo Limon, PhD, Geophysicist, PartnerRe

Robin Gee, MSc, Seismologist, PartnerRe

Paul Della-Marta, PhD, Head of Catastrophe Research, PartnerRe

This article is for general information, education and discussion purposes only and does not in any way constitute legal or professional advice.

References

Allen, T. I., and Wald, D. J.(2009). On the use of high-resolution topographic data as a proxy for seismic site conditions (Vs30), Bulletin of the Seismological Society of America, 99, no. 2A, 935-943.

Di Giacomo, D., E.R. Engdahl and D.A. Storchak (2018). The ISC-GEM Earthquake Catalogue (1904–2014): status after the Extension Project, Earth Syst. Sci. Data, 10, 1877-1899, doi: 10.5194/essd-10-1877-2018.

Ornthammarath, T., Jirasakjamroonsri, A., Pornsopin, P. et al. (2023). Preliminary analysis of amplified ground motion in Bangkok basin using HVSR curves from recent moderate to large earthquakes. Geoenviron Disasters 10, 28. https://doi.org/10.1186/s40677-023-00259-0

Stewart, J. P., et al., 2017. Expert panel recommendations for ergodic site amplification in central and eastern North America. PEER Report 4.

Storchak, D.A., D. Di Giacomo, I. Bondár, E.R. Engdahl, J. Harris, W.H.K. Lee, A. Villaseñor and P. Bormann, 2013. Public Release of the ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009). Seism. Res. Lett., 84, 5, 810-815, doi: 10.1785/0220130034.

Storchak, D.A., D. Di Giacomo, E.R. Engdahl, J. Harris, I. Bondár, W.H.K. Lee, P. Bormann and A. Villaseñor (2015). The ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009): Introduction, Phys. Earth Planet. Int., 239, 48-63, doi: 10.1016/j.pepi.2014.06.009.