Tectonic Relationships and Structural Development between Arjosari, Pacitan, East Java and Tawangmangu, Karanganyar, Central Java

Abstract

Java Island has volcanic arcs at the south and at the middle which are spread in a east-west pattern called Southern Mountains Zone and Quaternary Mountains Zone. The east-west pattern resembles the structural pattern produced by the Java tectonic subduction. Based on this, research was carried out to determine tectonic relationships and structural development in the Southern Mountains Zone and the Quaternary Mountains Zone. The study was conducted by structural mapping of each zone, namely the Grendulu Fault in Pacitan Regency which belongs to Southern Mountain Zone and the Cemorosewu Fault in Karanganyar Regency which belongs to Quaternary Mountains Zone. The mapping shows that the Grendulu Fault is a horizontal fault with north-south main stress, while the Cemorosewu Fault is a normal fault with nearly vertical main stress. Based on these, it can be concluded that there is no direct, but indirect tectonic relationship that works between the two: both structures developed due to Java Subduction. The structural development of the Grendulu Fault is strongly influenced by Java Subduction, which the subduction gives north-south main stress that forms this fault. While Southern Mountains formed, Kendeng Basin was formed due to loading from the mass of Southern Mountains. The formation of Kendeng Basin was continued with the formation of the Mount Lawu Complex (part of Quarternary Mountains) where the Cemorosewu Fault developed. This fault is formed as a result of mass loading of the Mount Lawu itself and triggered by the slope from Kendeng Basin to the north.

Structure Interpretation Using Gravity Spectral Analysis and Derivative Method in Grindulu Fault, Pacitan, East Java

“…The structures developed are mostly complicated as they were contolled by various main stresses of different tectonic regime. Pacitan is located in transition zone between cretacous subduction trend dominated and tertiary subduction trend dominated [3]. This makes the structures formed in Pacitan have several dominant trends and develop into different types of faults.…”