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Abstract:
In order to understand the subsurface velocity structure of the city of Yangon, Myanmar, microtremor observations were conducted in and around the city. Data was obtained during the period of 2015 to 2018. Triangular array observations were conducted at seven locations within the study area in order to estimate the phase velocity and the velocity structure at each location. On the other hand, in order to estimate the depth distribution of the subsurface layers, single-station observation was conducted at over 150 sites to obtain Microtremor horizontal-to-vertical spectral ratios (MHVRs) (Hirokawa et al., 2016; Matsushita et al., 2018).These data will be reinvestigated to reexamine the subsurface structure of the city of Yangon. The S-wave velocity and thickness of the layers is estimated from the phase velocity and P-wave velocity and density are estimated from the S-wave velocity using the relation by Ludwig et al. (1970). The velocity structure at singe-station observation points are estimated by fitting the observed MHVRs with the theoretical MHVRs calculated according to the diffuse field concept (Sánchez-Sesma et al., 2011) using the velocity structure estimated at the array observation locations as initial models. The S- and P-wave velocities and number of layers are fixed and only the thickness of the layers are changed to fit the data. The estimated velocity structure will be interpolated to construct a three-dimensional velocity structure and the amplification factor due to the subsurface structure is estimated.
