Paleo-earthquakes recorded on marine terrace in the Mumaung Island, western Myanmar

We found geomorphological evidence of intermittent abrupt sea level changes associated with earthquakes that occurred along the Rakhine coast of western Myanmar, facing the plate-boundary north of the 2004 Sumatra-Andaman earthquake source. Based on air-photo interpretation, we identified Holocene marine terraces divided into at least four (partly six) steps that named L1-4 in descending order along the coast of the Mumaung Island. To measure its height and age, we conducted field survey at 5 sites in the island. The height of each steps are measured to be L1: 15-18m, L2: 12-14 m, L3: 7-10 m and L4: 3-5 m above mean sea level. The lowest terrace, L4, can be correlated to the 1762 Bengal earthquake because samples collected from in-situ uplifted oyster reef and micro atoll are dated to AD1430-1860 by AMS measurement. Amount of uplift of the 1762 event is estimated to 3-5 m in minimum, which is consistent with previous reports of Halsted (1843) and Mallet (1878). Higher terraces are radiocarbon-dated to be L2: AD 680-980 and L3: 150 BC-AD 60. Although reliable sample could not be obtained from the L1 terrace, it is probably correlated with the highest terrace along the coast of Phayonkar Islands, further north of the Mumaung Island, which was dated to 1295-600 BC by Aung et al. (2008). We thus conclude that large earthquake as well as the 1762 event accompanied with uplift of 3-5 m has recurred with interval of about 900 years.