Measurement of Shear Strain in Map Liquefaction Area for Earthquake Mitigation in Bengkulu City

Abstract

Bengkulu city is well-known as a high-risk area for an earthquake. One of the effects of the earthquake is liquefaction, the phenomenon in which the strength and stiffness of the soil are reduced by shock. The researchers measured the quantity of liquefaction by knowing the value of Vs30 values that can be obtained from the United States Geological Survey (USGS). In this study, however, we measured liquefaction based on the shear strain value (γ). Here, the shear strain values could be determined by measuring the seismic vulnerability index and the peak ground acceleration. The vulnerability index was obtained by measuring the resonance of the frequency and the amplification factor using a short period seismometer with 3 components (2 horizontal components and 1 vertical component), whereas the peak ground acceleration was obtained from the earthquake data that happened in Bengkulu City in 2000. The result showed that Vs30 and shear strain negatively correlated.

Seismic Vulnerability Maps of Ratu Agung District, Bengkulu City, Indonesia

“…The shear strain value range and its resulted phenomena were compiled by Ishihara [20] (shown in Table 1). By following the strain dependences shown in Table 1, Nakamura [19] derived the formulation of  (shear strain) linked to Kg which is shown in Equation 3. In its result, the estimation of shear strain is then referring to the limitation of shear strain presented in Table 1.…”

“…The prediction of PGA in this study area seems to be consistent with massive liquefaction found in this location during the Bengkulu-Mentawai Earthquake 2007, since in in overall, the predicted PGA in the study area has exceeded the minimum requirement of PGA to trigger liquefaction. From the interpretation of PGA presented in Figure 11, the ground shear strain can be estimated by Equation 3. The ground shear strain in the study area is presented in Figure 12. In general, the interpretation shows the ground shear strain in the location is of about 10 -3 .…”

“…A strong earthquake occurred on September 12, 2007, which was later known as the Bengkulu-Mentawai Earthquake, has raised many questions to the geotechnical engineers and geophysicists. The main issues related to this event are liquefaction phenomenon along coastal area [1], the reliability of seismic design code [2], and the seismic vulnerability and microzonation maps for the seismic hazard mitigation in Bengkulu [3]. One of the areas in Bengkulu City that was undergoing the significant damage during the Bengkulu Mentawai Earthquake in 2007 was Ratu Agung District ( Figure 1).…”

“…One of the areas in Bengkulu City that was undergoing the significant damage during the Bengkulu Mentawai Earthquake in 2007 was Ratu Agung District ( Figure 1). Several researchers such as Mase [1], Farid and Hadi [3] and Refrizon et al [4] reported that geotechnical damages could occurred during the earthquake in this region.…”

“…Several researchers, such as Mase [1,2,5], Farid and Hadi [3], Refrizon et al [4], Mase and Somantri [6], and Mase [7] had studied the earthquake impact and another related phenomenon called liquefaction damage during the Bengkulu-Mentawai Earthquake on September 12, 2007.…”