Indonesia's Geotectonic Context: Bali and Surrounding Areas

Thursday, 01 February 2024

Indonesia is situated at the convergence of three major tectonic plates: the Eurasian Plate, the Indo-Australian Plate, and the Pacific Plate. The island of Bali and its surroundings are part of Indonesia's seismotectonic landscape. This region is traversed by the Mediterranean mountain belt and includes a subduction zone resulting from the interaction between the Eurasian Plate and the Indo-Australian Plate. The boundary of this interaction forms an oceanic trench located south of the Java, Bali, and Nusa Tenggara island chains.

Tectonic Movements and Research Findings:

• Indo-Australian Plate Movement:
  • The movement of the Indo-Australian Plate towards the Eurasian Plate was first estimated using Global Positioning System (GPS) research in 1989.
  • The study revealed that the relative movement of Christmas Island (located on the Indo-Australian Plate) against West Java (on the Eurasian Plate) is 67±7 mm/year in the direction of N11°E±4° (Tregoning et al., 1994).
  • This result closely matches the theoretical calculation using the NUVEL-1 model, which estimated 71 mm/year in a direction slightly more north at N20°E±3° (DeMets et al., 1990).

Seismic Activity in Bali:

• Due to these tectonic conditions, Bali experiences a high level of seismic activity associated with plate subduction beneath the Sunda Shelf and the active margin of the Australian continent, as well as the continuation of the Sunda Arc towards the east, where it meets the Banda Arc.
• Tectonic Features:
  • The movement of these plates results in characteristic tectonic features of subduction systems, including oceanic trenches, Benioff zones, outer arc basins, foreland basins, and mountain ranges.
  • Beneath Bali, there is a seismic zone with a slab reaching depths of 100 km and dipping at an angle of 65°, extending to a depth of 650 km beneath the northern part of the island.

Geological Characteristics:

• Benioff Zone: Rocks in this zone include alkaline igneous rocks and volcanic products (volcanoes).
• Java-Bali Trench: The continental slope rising from the Java-Bali Trench is characterized by sediment imbrication and mélange, with thrust faults being the main structural features of the outer arc ridge area.
• Outer Arc Basin: This basin extends between the outer arc ridge and the volcanic arc.

Recent Earthquakes:

• The recent earthquakes are a result of the tectonic plate shifts described above. For information on earthquakes in the past month, visit: BMKG Earthquake Information.

(Source: BMKG Indonesia)

 

 

 

 

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