Does Singapore have active faults? Geological investigations in an unprepared, urbanized tropical city–state

Aron J. Meltzner, Wanxin Huang, Matthew Xiang Hua Foo, & Mason K. Perry

Submitted September 7, 2025, SCEC Contribution #14476, 2025 SCEC Annual Meeting Poster #TBD

Singapore, a highly urbanized city–state of 6 million on a ~730 km2 island, is commonly believed to be “safe” from local earthquakes, with only distant Sumatran earthquakes thought to affect it. This view likely arises from the scarcity of recorded local events since Singapore’s founding in 1824, yet it overlooks two M ≥ 5 earthquakes within ~120 km to the north and northwest in 1922, and a 1948 event — reported only from the island’s southern–central area — that produced EMS intensity IV–V at multiple closely spaced sites, suggesting a local source. Recent mapping has revealed numerous bedrock faults in Singapore, but their capability remains unstudied.

The Downtown Core of Singapore, in the southern–central part of the island, is built atop the low-lying Kallang Basin and adjacent reclaimed land. Sediments, likely MIS 5e (120 ka) and younger, fill the basin to 40 m depth in the west but thin eastward; immediately to the west, Cretaceous to Pliocene bedrock rises up to 50 m above sea level. The steep, unconformable contact between bedrock and overlying layers has been interpreted as either a sea cliff or an inactive fault. We hypothesize instead that it may be an active fault — either an east-dipping normal fault bounding a syndepositional half-graben or a transtensional stepover in a longer dextral fault system.

Using four decades of borehole data, we are mapping the subsurface architecture of Kallang Basin. The western margin of a buried Late Pleistocene channel follows the abrupt eastward deepening of the top of the bedrock, even though intervening deposits blanketed and buried the bedrock escarpment. This raises a question of whether the alignment of the channel and escarpment is coincidental or reflects structural control by repeated slip along an active fault.

Key Words
Singapore, boreholes, half-graben, transtensional, stepover, active faulting

Citation
Meltzner, A. J., Huang, W., Foo, M., & Perry, M. K. (2025, 09). Does Singapore have active faults? Geological investigations in an unprepared, urbanized tropical city–state. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology