Influence of Geomorphology and Siltstone Structure on the Land Vulnerability in Mamberamo Raya, Papua, Indonesia

Mamberamo Raya is one of the most prone areas in Papua, Indonesia, due to frequent earthquakes. The researchers analyzed the relationship between the pattern and direction of the fault-stress structure and geochemical characteristics of siltstone on land vulnerability. The fault structure and land vulnerability pattern and direction were analyzed from the direct interpretation of the Digital Elevation Model map, outcrop descriptions, petrography, stereology, rainfall classification, earthquake estimation curves, landslide data. Siltstone geochemical characteristics were collected from selected rock outcrops that were outside the fault structure area. In each location, claystone, sandstone, and siltstone samples were collected before identifying at the Optical Mineral Laboratory in the Department of Geology, Hasanuddin University. The pattern and direction of the fault-stress structure and the siltstone geochemical characteristics affected the land vulnerability. The trend of seismic activity was highly associated with regional-scale faults, such as the fold and thrust fault belt of Guinea, Gauttier-Roufaer Central Range fault, Sarmi fault, Waropen fault, and Mamberamo fault. The earthquake dynamics that affected the southern part of the local-scale fault area were overlapped with an area of stripped rock with the shear plane. There were alternating sandstone, greywacke, claystone, and siltstone layers with chemical compositions of Al, Ca, Fe, K, and Mg and the age of the rock formation. The shear plane vulnerability may cause soil erosion and unstable slopes. Based on the mapping results, the areas with extremely high vulnerability were found in northeast Anggreso, north of Pioneer Birak, and the southwest of Kasonaweja. Moreover, high-vulnerability areas are also detected on the hillsides south of Burmeso, while the land vulnerability in Kanonaweja and Burmeso was classified as medium or low. The outcrop existence and stripped rock with shear plane highly influence the silt-stone structure on the land susceptibility in the studied area.