2011 : Assesment to the Local Site Effects during Earthquake Induced Landslide Using Microtremor Measurement (Case Study: Kemuning Lor, Jember Regency-Indonesia)
Dr.Ir. Ria Asih Aryani Soemitro M.Eng.
In Kemuning Lor village–Jember regency–East Java, The local site of geology and topographic on ground motion during earthquake induced landslide were investigated using Horizontal to Vertical Spectra Ratio (HVSR). The microtremor measurements were performed at the landslide area on 82 free-field measurement having 20 x 20 m dense grid. The amplification factor (Am) in 2-7 range and the soil natural frequency (fo) in 1-3 Hz were obtained from the HVSR analysis. The fo value had changed with the topographic pattern. The bedrock surface might be estimated using the fo value. The Am highest value was found at the main scarp landslide and at the slope area having high topographic gradient. Variations of fo and Am parameters were indicated as surface soil parameter’s variations. In general, the local geology effects is more dominant than the topography effect. The level of soil damage due to the local site effects at the landslide location was indicated by the vulnerability index (kg) and the effective shear strain (γ). Generaly, vulnerability index (kg) varied from 2.6 to 34.6 and the γ values varied from 500 x10-6 to 6700 x 10-6. This paper illustrates how the vulnerability index and the effective shear strain could be used to make preliminary assessment of the main scarp area failed during the earthquake.