yrammuS 要概119Johan Arif120Wahyu SrigutomoEnvironment in Rembang Zone in East Java during Plio-Pleistocene based on limestone formation-based of climate change (Project 2018)Development of 3-D Magnetotelluric Finite Element Modeling and Efficient Non-Linear Inversion in Volcanology and Geothermal System (Project 2018)79Rep. Grant. Res., Asahi Glass Foundation (2019)The purpose of this research is to study whether environmental change caused by climate change occurred in the past in the tropic. For this research, Lidah Formation which spreading in the Rembang and Randublatung Zones in East Java will be studied. The research is concentrated on Turi Member of Lidah Formation and the description is carried out at three location namely: Gandong river (Mojodelik village), Kalitidu river (Ngadi-luwih village) and Pencol river (Bareng village) at Bojonegoro regency. Oxygen isotope analysis was carried to some molluscs shell from the lower to the upper parts of Turi Member of Lidah Formation. The result indi-cates when limestone formed, including coquina limestone at the upper part, the sea water inclined to be warmer. Perhaps, the limestone was formed in the Pliocene and Late Pleistocene, when the CO2 was abundant.In recent decades the use of the magnetoteluric (MT) method in geophysical exploration and geosciences stud-ies increased significantly. Due to its rapid development in terms of technology and equipment, a better under-standing of interpretation techniques from MT data is required. Interpretation techniques in MT data have been developed through numerical modeling both in 1 dimension (1D), two dimensions (2D) and 3 dimensional (3D). 3D inversion in the MT method is necessary to overcome the ambiguity of the results of 1D and 2D in-versions. The solution to the 3D MT inversion problem is non-trivial because of its non-linear and large-scale. So that a reliable inversion program is needed with time and computing memory that is quite efficient. In this study, the data space Occam's non-linear inversion algorithm used using an edge-based finite element approach with a hexahedral element to increase accuracy and convergence levels. The solution of linear equations will be solved using an iterative method with a preconditioned conjugate gradient (CG) to accelerate the conver-gence rate.
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