Active faults in Indonesia

Tjia, H. D. (1978) Active faults in Indonesia. Bulletin of the Geological Society of Malaysia, 10. 73 -92. ISSN 2637-109X

Abstract

The recognition of active faults is of obvious importance to urban planning, engineering projects and earthquake studies. A preliminary classification of faults according to their states of activity comprises four classes. (1) Active faults occurring in Holocene deposits or associated with historical earthquakes, disturbances to man-made structures and to regular plant distribution patterns, deformation of alluvial deposits and live reef platforms. (2) Potentially active faults in Quaternary deposits, earthquake-prone areas or active volcanoes. (3) Faults of uncertain activity occurring in pre-Quaternary rocks in tectonically mobile regions and without information about their displacements. (4) Inactive faults in pre-Quaternary, tectonically stable areas that are not underlain by limestone or exist far from steep slopes. The known principal zones of active faulting in Indonesia comprise several strike-slip fault belts (Sumatra fault zone, 1600 km long; Palu-Koro fault zone, 700 km long; Irian fault zone that on land is 1300 km long); the central depression of Timor where normal faulting is associated with lateral displacements; the Banyumas depression of Java; active volcanoes (with records from Tangkubanperahu, Merapi, Kelut all in Java and Krakatau in Sunda Strait), where principally normal faulting takes place through tectono-gravity causes; extensive limestone terrains (Gunung Sewu, Java; Maros area, South Sulawesi; Ayamaru plateau, Irian Jaya) where normal faulting occurs through undermining. Only few examples of active thrusting are known to the author. Recorded single-event displacements by strike-slip motion amount to a few metres but are generally of shorter distances. Single displacements on active normal faults may create throws of up to 10 metres.

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