IDENTIFICATION OF ROCK LAYER CONTACTS IN THE SURROUNDING OF THE SUTAMI DAM USING GEOMAGNETIC METHODS.

Research on rock layer contact at Sutami Dam, Karangkates Village, Sumberpucung District, Malang Regency, Indonesia was undertaken. This research was conducted to identify volcanic sediments layers' which contact with Limestone Sediments in the surrounding of Sutami Dam and to mitigate potential disasters in the dam's surrounding area. This research was conducted by a geomagnetic method. Data were collected using the Proton Precession Magnetometer G-856. The geomagnetic data acquisition started from the Kromengan District (112.494oE; 8.129oS) to the Sukorame District (112.358oE; 8.213oS). The radius of geomagnetic data acquisition was 15 km; the space between the points was 300 meters with 1372 measurement points. The value of the geomagnetic intensity are between -210 nT to 514 nT. The northern part of the research location has a lower total geomagnetic intensity than the southern area. The northern part is thought to be volcanic sediment (Tuff Desposits and Butak Volcanic Sediments), which only covers the surface, while the southern part is (Limestone Sediments) Marine sediment, which is some parts thought to have been volcanoes in ancient times. The ancient volcanoes in the southern part are Mounts Golo, Selorejo, Selumban, Tretes, Soko, Pehlembun and Krowedul. The contact layer between volcanic sediments with Limestone Sediments is more difficult to consolidate, so that the buildings built on them are more vulnerable. [ABSTRACT FROM AUTHOR]