Seismic Microzonation Of Core Area Of Madhyapur Thimi Municipality Using Microtremor Observation

Abstract

Located to the east of Kathmandu, Thimi is a historic town with dense settlements including many modern and traditional houses, historic monuments, and other important institutional buildings. The town lies in a seismically active region and has suffered from major earthquakes in the past. Because of the combination of seismicity and being a densely populated area, studies of seismic activity and local geology in the area are very important. In this research, we conducted a passive source microtremor survey method at 92 locations. The study area covers about 3.5 km2 of the core area of Madhyapur Thimi Municipality. The study area was divided into 200m x 200m grids and microtremor readings were taken at grid points. From HVSR analysis, most of the stations show flat H/V curves. The flat curve of the H/V curve is very likely due to the local underground structure, which does not exhibit any sharp impedance contrast. This may be the reason for comparatively less damage suffered by Thimi than other towns in the valley. The inversion technique is used to determine the shear wave profile of the site. The result of the inversion shows the surface velocity is close to 200 m/s.