DEEP AND SHALLOW STRUCTURES OF GEOTHERMAL SEULAWAH AGAM BASED ON ELECTROMAGNETIC AND MAGNETIC DATA

Abstract

Indonesia is a country with the largest geothermal reserves in the world, but exploration and
utilization of geothermal energy are still low. As an effort in increasing exploration process, an integrated
geophysical method to image the subsurface structure of the geothermal system has been done at Seulawah
Agam Geothermal Field, Aceh Province, Indonesia. Very low frequency (VLF-R) method was used for shallow
and magnetotellurics method for deep structures studies in the area. The magnetic method was used for a
complementary of the electromagnetic methods. Magnetotelluric data were acquired at ten stations along a 30
km distance profile crossing the Seulawah Agam volcano in a north-south direction. The VLV-R and Magnetic
stations were measured on the Ie Ju manifestation area only, located at the northern slope of the volcano. The
magnetic and VLF-R methods have been able to investigate the local structure, while the regional structure of
subsurface is described by the magnetotelluric method. 2D resistivity model of magnetotelluric data shows a
conceptual model of the geothermal system based on resistivity variation. The model also reveals two local
faults crossing the volcano in a northwest-southeast direction. Most of the geothermal manifestations in
Seulawah Agam are controlled these faults. Application of VLF-R and magnetic methods on the Ie Ju
manifestation area has shown clearly near surface structures of the area. The inverted models have strong
agreement with a reduction to the pole of total magnetic field anomalies. Presence of the conductors in the
resistivity models coincides with low total magnetic field anomalies. In addition, the total magnetic field
anomalies map can be also used to locate the presence of geothermal manifestation with or without their
appearance on the surface.