Indonesian Journal on Geoscience

Number 1 vol 3, 2016

5
Template JLBG

Authors: JLBG

Abstract

View in PDF

Number of views: 3072

Template JLBG

6
TEMPLATE

Authors: IJOG

Abstract

View in PDF

Number of views: 395

The Template

10
Hydrogeological Model of an Urban City in a Coastal Area, Case study: Semarang, Indonesia

Authors: Thomas Triadi Putranto and Thomas R. Rüde

Abstract

View in PDF

Number of views: 438

In Semarang City, groundwater has been exploited as a natural resource since 1841. The groundwater exploited in deep wells is concentrated in confined aquifers. The previous hydrogeological model was developed in one unit of aquifer and refined then by using several hydrostratigraphical units following a regional hydrogeological map without any further analysis. At present, there is a lack of precise hydrogeological model which integrates geological and hydrogeological data, in particular for multiple aquifers in Semarang. Thus, the aim of this paper is to develop a hydrogeological model for the multiple aquifers in Semarang using an integrated data approach. Groundwater samples in the confined aquifers have been analyzed to define the water type and its lateral distribution. Two hydrogeological cross sections were then created based on several borelog data to define a hydrostratigraphical unit (HSU). The HSU result indicates the hydrogeological model of Semarang consists of two aquifers, three aquitards, and one aquiclude. Aquifer 1 is unconfined, while Aquifer 2 is confined. Aquifer 2 is classified into three groups (2a, 2b, and 2c) based on analyses of major ion content and hydrostratigraphical cross sections.

15
Kinematic Analysis of Fault-Slip Data in the Central Range of Papua, Indonesia

Authors: Benyamin Sapiie

Abstract

View in PDF

Number of views: 622

Most of the Cenozoic tectonic evolution in New Guinea is a result of obliquely convergent motion that led to an arc-continent collision between the Australian and Pacific Plates. The Gunung Bijih (Ertsberg) Mining District (GBMD) is located in the Central Range of Papua, in the western half of the island of New Guinea. This study presents the results of detailed structural mapping concentrated on analyzing fault-slip data along a 15-km traverse of the Heavy Equipment Access Trail (HEAT) and the Grasberg mine access road, providing new information concerning the deformation in the GBMD and the Cenozoic structural evolution of the Central Range. Structural analysis indicates that two distinct stages of deformation have occurred since ~12 Ma. The first stage generated a series of en-echelon NW-trending (π-fold axis = 300°) folds and a few reverse faults. The second stage resulted in a significant left-lateral strike-slip faulting sub-parallel to the regional strike of upturned bedding. Kinematic analysis reveals that the areas between the major strike-slip faults form structural domains that are remarkably uniform in character. The change in deformation styles from contractional to a strike-slip offset is explained as a result from a change in the relative plate motion between the Pacific and Australian Plates at ~4 Ma. From ~4 - 2 Ma, transform motion along an ~ 270° trend caused a left-lateral strike-slip offset, and reactivated portions of pre-existing reverse faults. This action had a profound effect on magma emplacement and hydrothermal activity.