Agus Setyawan

Lithology and characteristic of landslide in Gombel Hill by 2D geoelectric resistivity method using dipole-dipole configuration

Gombel hill locates at Semarang, Central Java, Indonesia. Base on Semarangs susceptiblity map zone, Gombel hill is belong to high susceptibility and instability zone. Instability may cause faults to Gombel hill area, unfortunately the geosciences research in Gombel is still lack. The geophysical survey has been conducted using 2D geoelectric resistivity method with dipole – dipole configuration to identify the lithology of landslide at Gombel hill. The data have been collected from three lines. The first and third line have 100 m length, and the second line have 80 m length with 5 m space in each lines. The data were processed and modelled using Res2Dinv software. From the first line, suspected there are two layers which formed the structure of the subsurface. The second line suspected there are three layers which formed the structure of the subsurface. And the last line suspected there are two layers which formed the structure of the subsurface. Overall, the landslide of Gombel hill area can be found with depth 5 m – 6 m and found at contact between clay and clay rock layer. We expect the results can be used for mitigation hazard and planning the developing infrastructure in Gombel area.

Sea Water Intrusion in Kaligawe Semarang Based on Resistivity Data

Semarang is a city on the north coast of the island of Java, Indonesia and it is lowland areas have experienced sea water intrusion. One of interesting area is Kaligawe which located at Eastern part of Semarang. Kaligawe has big population and industrial and it need water consumption. Excessive extraction of groundwater will be resulting height difference surface ground water to the surface of the sea water due to sea water intrusion. Electric resistivity method was used to detect for salt water intrusion. Dipole-dipole configuration was applied with 3 lines to get current, potential difference, and apparent resistivity from the field. 2D model has presented using Res2Dinv to get the true resistivity and the depth of each layer. A calibration of the model was conducted based on geological information. Result showed the subsurface area has 4 layers: sandstone, sandsilt, siltstone and clay. Moreover the sea water intrusion occurs in the Northwest, East and Southern part of the study area