On 28 September 2018, a strong earthquake (Mw 7.5) struck Donggala Regency triggering flow liquefaction (locally termed Nalodo) phenomena in two residential areas in Palu City. Mitigating such an earthquake collateral hazard requires understanding the geological condition controlling such liquefaction. This paper presents a geophysical study to clarify the geological condition controlling the Nalodo phenomena in Palu City. The objectives of this study were to estimate shear wave velocity (Vs) profiles in the Nalodo and non-Nalodo sites and evaluate liquefaction potential based on the shear wave velocity profiles. The study involved a series of array microtremor surveys in two Nalodo sites and three non-Nalodo sites in Palu City. The results show that Vs generally increases with depth but varies from one site to another. Based on the Vs profiles, a thick soil layer with Vs of less than 175 m/s is present from the ground surface in the Balaroa and Petobo sites. Contrary, this soil layer is detected at a deeper depth in the non-Nalodo sites. Based on the liquefaction potential analysis, the near-surface soil layers in the Balaroa and Petobo sites are clearly liquefiable for all the PGA values used in this study. Although deeper soil layers can also be liquefied, no liquefaction occurred in non-Nalodo sites because a thick medium soil layer exists near the surface. Thus, a thick soil layer with Vs of less than 175 m/s near the ground surface controls the Nalodo phenomena in Palu City. Further studies to clarify other factors controlling flow liquefaction are recommended.
ABSTRAK Secara geologi, wilayah Cekungan Bandung tersusun oleh endapan danau Bandung purba yang terdiri atas lapisan lempung dengan sisipan lapisan pasir sehingga rentan terhadap likuifaksi akibat gempa bumi. Metode analisis multi-sensor gelombang permukaan (MASW) adalah salah satu metode geofisika yang menghasilkan model satu dimensi kecepatan gelombang geser (Vs) terhadap kedalaman. Makalah ini menyajikan hasil analisis potensi likuifaksi menggunakan data profil Vs di 5 lokasi yang tersebar di wilayah Cekungan Bandung. Data Vs diperoleh dengan menggunakan 24 geophone yang tersebar dengan spasi 4 meter di setiap lokasi penelitian. Hasil analisis data menggunakan metode MASW menghasilkan profil Vs dan Vs30 di setiap lokasi yang menunjukkan bahwa lapisan tanah di wilayah Cekungan Bandung dapat diklasifikasi dalam kelas situs E dan D. Sedangkan berdasarkan hasil analisis potensi likuifaksi menggunakan profil Vs, dengan mempertimbangkan percepatan tanah puncak yang dihasilkan oleh Sesar Lembang (M w 6,5), mengindikasikan bahwa lapisan pasir di dalam endapan danau purba mempunyai potensi likuifaksi pada kedalaman dan ketebalan yang bervariasi. Lapisan pasir dengan nilai Vs < 175 m/detik yang menyebabkan potensi likuifaksi di daerah Bojongemas lebih tinggi dibandingkan dengan daerah lainnya. Hasil penelitian ini menunjukkan kesesuaian dengan hasil analisis likuifaksi berdasarkan metode uji penetrasi standar dari hasil penelitian terdahulu.Kata kunci: gelombang permukaan, kelas situs, kecepatan gelombang geser, likuifaksi, MASW ABSTRACT − The Evaluation of Liquefaction Potential in Bandung Basin Area Based on Multi-Channel Analysis of Surface Wave. The Bandung Basin region is composed of ancient Bandung lake sediment deposits consisting of thick clay layers intercalated with sand layers, which is vulnerable to liquefaction due to earthquakes. The Multi-channel Analysis ofSurface Wave (MASW) analysis method is a geophysical method that produces a onedimensional model of shear wave velocity (Vs) against depth. This paper presents the results of an analysis of the potential for liquefaction using Vs profile data at 5 locations spread across the Bandung Basin. using 24 geophones with 4-m spacing. The results of data analysis using the MASW method produce Vs and Vs30 profiles at each location which indicate that the soil layers in the Bandung Basin area can be classified into E and D site classes. Meanwhile, based on the results of the analysis of potential liquefaction using the Vs profile, taking into account the peak soil acceleration produced by the Lembang Fault (Mw 6.5), indicates that the sand layer in ancient lake sediment deposits has the potential for liquefaction at varying depths and thicknesses. Sand layer with a value of Vs <175 m / sec which causes the potential for liquefaction in the Bojongemas area is higher than in the other areas. The results of this study confirm liquefaction analysis based on the standard penetration test method from the previous study.
Dye-Sensitized Solar Cell (DSSC) is one of photovoltaic (PV) cell which converts solar energy into electrical energy, by using dye as its active material. In this study, total energy and bandgap energy of natural dyes such as theaflavin and cyanidin-3-glucoside (C3G) molecules were calculated using density functional theory (DFT) method via quantum espresso software. Optimization of some calculation parameters such as cutoff energy, pseudopotential and k-point have been done to ensure minimum total energy of dyes molecule. Based on the result, the total and bandgap energy of theaflavin is 10172.80 eV and 1.96 eV, while the total and bandgap energy of the C3G molecule is 8442.26 eV and 1.73 eV. From these results, further investigation is necessary to the opportunities of the two dyes as DSSC sensitizers.
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