STUDY OF SEPTEMBER 28th 2018 TSUNAMI DEPOSITS BASED ON SEDIMENTOLOGY, GEOCHEMISTRY AND FORAMINIFERA CHARACTERISTICS IN REGION OF LESEHAN, PALU, CENTRAL SULAWESI

• Main Author: Nur Faqih An Nahar, Rikza
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/40422
• Institution: Institut Teknologi Bandung

Based on BMKG data, September 28th, 2018 at 17.22 WIB a tsunami has occurred in the areas of Palu, Donggala, and Mamuju, Central Sulawesi. The cause of the tsunami in Palu was a submarine landslides resulted by a great earthquake. It was proved by 10 coastal collapse zones arround the bay. Field surveys of tsunami deposits have been conducted, but there is no further analysis to determine the characteristics of deposits. The purpose of the study is to determine the characteristics of the landslides tsunami deposits in Lesehan Palu, determine the dynamics of each run up tsunami wave (3 waves) based on their characteristics of the sediment, determine the effect of the distance from the shoreline due to the sediment characteristics, also to determine the distribution of foraminifera in tsunami deposits and their relation to tsunami deposition mechanisms. The location of the study is the East coast of Palu in Lesehan region. Spot sampling object are taken every 10-15 m on a 275 m transect away from the shoreline with a total of 52 samples and detailed analysis is done every 1 cm interval vertically in each spot. The grainsize analysis, geochemitry analysis (X-Ray fluorescence and loss on ignition), also analysis of foraminifera assemblages is used in this study. Generally, the September 28th 2018 landslides tsunami sediment characteristics for the Lesehan area shows specific characteristic in lateral and vertical. But in summary it will shows with brackish of fine grainsize, with fining upward sequence in each spot and fining and thinning landward, 2-10 cm in thick, relatively unimodal in mode although still a lot of coarse fraction, 1,124 phi - 5,729 phi in size (coarse silt - medium sand), poorly sorted - very poorly sorted, 0.97 % - 27,639% organic content material, 2.796% - 41.44% carbonate content material, 4678 - 75300 ppm and 107-1537 ppm in abundance of Ca and Sr also dominated by benthic foraminifera with transitional until middle neritic environment. The dynamics of 3 run up waves are reflected in bivariate diagram analysis and the multiproxy clustering analysis. The effect of distance from shoreline shows the tsunami deposits has fining upward trend and getting finer also thinner to landwards. Content of mud also being more abundant as the depth increasing and far away from the shoreline but being lack in state of increasing the depth of topography. The influence of lower micro-topography will cause grain size relatively coarser than in higher micro-topography. Poorly sortation, higher Ca and Sr content will be obtained when tsunami waves are blocked by high micro-topography. The distribution of foraminifera is more abundant in line of increasing depth. While laterally further away from the shoreline, it shows fewer individuals and species. The sources of tsunami deposits sediment are marine sediments eroded from the transition zone to the middle neritic (0-100 m).