Understanding the tectonic deformation of 1762 Arakan Earthquake
The objective of this project is to understand the seismic hazard associated with Arakan segment of the northern Sunda subduction along SE Bangladesh. In order to do that, it is necessary to document geologic evidence for the 1762 Arakan earthquake and prior events, to help estimate the recurrence interval (repeat time) for that earthquake. Historical records described that the 1762 earthquake caused extensive damage along the Arakan segment of the Sunda subduction system. But the geologic evidence for the earthquake farther north is necessary to better understand its associated seismic hazard to the densely populated nation of Bangladesh. This dissertation presents the results obtained from U/Th dating of the dead and live coral microatolls including their elevations measured by high precision GPS from the Saint Martin’s Island, DEM analysis and elevation of terraces from Teknaf coast and fault dislocation modeling based on the data obtained from the Saint Martin’s Island and Teknaf.
Coral microatolls from Saint Martin’s island documents the evidence of the 1762 and prior earthquakes. The U/Th ages documents strong evidence of microatoll die offs related to the 1762 earthquake. The >2 m elevation difference between the dead microatolls and present-day living corals suggest that the microatolls died due to the coseismic uplift of 1762 Arakan earthquake. This dissertation also provides evidence for two additional earthquakes taking place in ~700 and ~1140 C.E. which suggests an earthquake recurrence interval of ~500 years.
Evidence of the 1762 Arakan and Prior Earthquakes in the Northern Sunda Subduction
Geomorphic studies documented three terraces along the coast of Teknaf. Several marine terraces have been previously documented along the west coast of Myanmar. The youngest of these terraces has been correlated to the coseismic uplift of 1762 Arakan along the Myanmar coast. The terraces along the coast of Teknaf are characterized by flat to semi-flat surfaces followed by sharp topographic rises. DEM (Digital Elevation System) analysis and GPS (Global Positioning System) survey documented 2 to 3 terraces. Among these three, the youngest terrace is possibly linked to the 1762 Arakan Earthquake but the ages have not been verified.
Modeling using the data obtained from Saint Martin’s Island, Teknaf and other published articles (for the west coast of Teknaf) suggest a fault dipping at 10-15° to the northeast. The result of coseismic slip inversion shows 15 - 25 m of reverse slip along the Arakan rupture segment, which was accommodated by the upper plate failure. Based on our results from coral microatolls, terraces and the modeling study, this dissertation suggests that this segment of the Arakan collision zone has the potential to cause a future earthquake of Mw>8 which can produce a devastating effect to the inhabitants of Bangladesh, Myanmar and Eastern India.
Michael S. Steckler (PI, geophysics, tectonics and stratigraphy)
Cecilia McHugh (sedimentology and paleontology)
Office of Naval Research