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Site Amplification Variability in Yangon, Myanmar Tracked by Regional and Local Seismic Phases From a Dense Nodal Array

Description: 

Yangon, the largest city in Myanmar is located at the convergence of the Yangon and Bago rivers and is home to more than 7 million people. As a part of the Irrawaddy delta system, this densely populated city sits on young water saturated alluvium that can amplify earthquake ground motions. The city is surrounded by several seismically active faults including the Sagaing fault, a major right lateral strike-slip fault that has historically produced M>7.0 earthquakes. In the west, active subduction of the India plate also has the potential to generate a megathrust earthquake of M>8.0. Assessing site response is critically important to understanding and elucidating the seismic hazard potential and necessary building codes that can minimize the loss of property and life from a large seismic event. We investigate site amplification beneath the city of Yangon using data from 110 three-component nodal seismometers that were deployed along three densely spaced profiles during the Myanmar Universities Seismic Experiment (MUSE). Isolating the site term is often difficult since seismic amplitudes depend on the source, path, attenuation (Q), and velocity structure of the earth. However, MUSE has such a small aperture where the source and path effects have a negligible impact on relative changes in the amplitudes for frequencies below 5 Hz. We use this fact to investigate both regional and local Lg and Sg amplitudes and measure the relative site amplification in different frequency bands. Our preliminary results show which parts of Yangon city have significantly higher site amplification (by close to two orders of magnitude). We observed coherent site response characteristics between both the Sg and Lg phases. We also found that the site terms correlate well with the shallow geological structure of the city. Our model of site amplification is important for mapping the seismic hazard potential and the high-resolution seismic micro-zonation of Yangon at the scale of city blocks.

Session: Crustal Imaging of High Seismic Hazard Regions

Type: Oral

Date: 4/20/2023

Presentation Time: 09:00 AM (local time)

Presenting Author: Md Mohimanul Islam

Student Presenter: Yes

Invited Presentation: 

Authors