Coral microatolls as a tool for subduction zone paleoseismology: Identifying rare events along the Sunda megathrust and the Manila trench

Aron J. Meltzner

Submitted August 12, 2018, SCEC Contribution #8404, 2018 SCEC Annual Meeting Poster #242

Over the course of a seismic cycle, the land and seafloor above a subduction zone rise and fall. These land-level changes are recorded by coral microatolls, coral colonies living near the base of the intertidal zone whose upper level of growth is tightly limited by exposure during low water. As these microatolls grow, their growth patterns reflect changes in relative sea level. Their skeletons allow us to infer a history of land-level changes, caused by gradual strain accumulation between earthquakes and sudden strain release during earthquakes. This, in turn, provides insight into subduction zone fault processes and allows us to recognize paleoseismic events that have occurred in past centuries.

In 2004, an unexpected Mw 9.2 rupture of the northern Sunda megathrust triggered a tsunami that took >230,000 lives across the Indian Ocean. Subsequently, our studies of microatolls in Sumatra, along with colleagues’ paleotsunami investigations, revealed that predecessors of the 2004 earthquake and tsunami had occurred ~600 and ~1000 years earlier. If these results had been known earlier, the 2004 catastrophe might have been anticipated.

Farther south, along the Mentawai section of the Sunda megathrust, microatolls have revealed that clusters of large earthquakes occur periodically, every ~200 years. Large (Mw ~8.8) ruptures occurred in 1797 and 1833, and the most recent cluster began in 2007. Patterns of uplift and subsidence recorded by microatolls suggest that another large earthquake, approaching the size of 2004, may occur in the Mentawai region in the decades ahead.

Along the Manila trench west of Luzon, no earthquakes of Ms >7.6 are known from the historical record, but is this fault capable of rare, much larger earthquakes? We have begun a microatoll study along the west coast of Luzon, and our findings should provide insight into the earthquake and tsunami potential along the Manila trench and in the South China Sea.

Key Words
paleoseismology, paleogeodesy, subduction zone, coral microatoll

Citation
Meltzner, A. J. (2018, 08). Coral microatolls as a tool for subduction zone paleoseismology: Identifying rare events along the Sunda megathrust and the Manila trench. Poster Presentation at 2018 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology