Estimating site amplification variability in Yangon, Myanmar, from a dense nodal seismic array

Md Mohimanul Islam, Patricia Persaud, Myo Thant, Khin Win, & Eric Sandvol

Published July 11, 2025, SCEC Contribution #14691

We explore a novel acquisition geometry that can be used to estimate the linear component of site amplification using a dense nodal seismic network installed in Yangon, Myanmar’s largest city. The city is surrounded by several seismically active faults, including the Sagaing Fault, which is capable of generating Mw > 7.0 earthquakes. As part of the Irrawaddy delta system, this densely populated city sits on young water-saturated alluvium that is likely to amplify earthquake ground motions. Assessing site response is crucial for understanding the seismic hazard potential to minimize the loss of property and lives. Using a dense seismic array comprised of 110 three-component nodes, we estimated the frequency-dependent site amplification pattern of Yangon from regional (Lg) and local (Sg) seismic phases. Since this acquisition geometry is not sensitive to Q or geometric spreading, this approach provides a fast and cost-effective way to estimate the linear component of site response as a function of frequency. Our Lg and Sg site response results identify regions with high site amplification that have significantly greater seismic hazard risks for regional and local distance earthquakes. We observed consistent site response characteristics between both Lg and Sg phases. Site amplification patterns correlate well with the surficial geology and subsurface structure beneath the city. De-amplification is observed across all frequencies at stations located above an anticlinal structure composed of older Pliocene rocks (i.e. the Irrawaddy Formation). Conversely, highly amplified areas correspond to younger Pleistocene to recent alluvial plains consisting of loose, unconsolidated alluvium. We found a dominant horizontal-to-vertical spectral ratio (HVSR) peak at ∼1.0 Hz from ambient noise, likely corresponding to the thickness of unconsolidated sediments. We suggest that the growing number of nodal networks worldwide can be used to estimate frequency-dependent site amplification, addressing key data gaps in seismic hazard assessment.

Key Words
Site amplification, dense nodal array, urban sedimentary basin

Citation
Islam, M., Persaud, P., Thant, M., Win, K., & Sandvol, E. (2025). Estimating site amplification variability in Yangon, Myanmar, from a dense nodal seismic array. Earthquake Spectra,. https://doi.org/10.1177/87552930251352843.