Late Holocene seismic uplift events depicted by coastal karst formations in Bali, Indonesia

Abstract

Limestone shores record earthquake-related uplift and subsidence worldwide. While comprehensive investigations exist for the Mediterranean and Japan, only limited studies are available in other regions. In this study, we analyze the carbonate shore of the Sunda Arc on Bali Island, Indonesia, in terms of tectonic uplift/subsidence. We surveyed coastal profiles of terraces and notches, identifying coastal karst features and bioerosion traces and determining their position relative to sea level. We found a set of marine terraces at Suluban Beach: Level A (lowest) – the active reef pavement with occasional surf potholes; Level B – 0.5–0.7 m above level A, with surf potholes and channels; Level C – 0.8 m above level B, heavily pitted by flat-bottomed pans, separated by heavily karstified ridges; Level D – 2 m above level C, karstified surface, with several decimetres deep karren. The increasing depth of coastal karst features marks a longer time of exposure to the sea, both in the intertidal and the supratidal zone. Holocene sea level reached its present-day position about 5000–6000 years ago; therefore, all coastal features, which require the action of the sea, salt water, and wave action to develop, formed following this period. Bali is on the front of the overriding plate in the Sunda arc. Seismicity is expressed by the uplift of the coastal zone. We propose that seismic events of moment magnitude 6.5–7, with a few hundred years return period, can produce the observed repeated surface uplift of 0.5–2 m in Bali.