Geologic Evidence for Three Great Earthquakes in the Past 3400 Years Off Myanmar

Abstract

Tectonic environments, recent stress and crustal strain observations, and historical descriptions of geomorphological changes and eyewitness accounts of the 1762 Bengal earthquake suggest that great earthquakes (M 8.0 or larger) can occur along the northward continuation of the 2004 Sumatra-Andaman earthquake. We describe marine terraces along the Rakhine coast of Myanmar as evidence for three great earthquakes in the past 3400 years. Radiocarbon dating of coral remains suggests that the oldest terrace emerged three times, during 1395–740 BC, AD 805–1220 and AD 1585–1810. We assign the youngest age to the 1762 earthquake, which reportedly raised parts of the Burmese coast by 3–7 m. These indicate that the great subduction-zone earthquakes have repeatedly occurred west off Myanmar with an average recurrence interval of about 1000–2000 years. The time since the last earthquake, ~ 250 years, is much shorter than the average interval, hence the chance of next earthquakes in the near future may be considered as low. However, the variability in both uplift amounts and recurrence intervals suggests the next great earthquake could happen sooner or later than would be expected from the average interval.

Sand Sheets on a Beach-Ridge Plain in Thailand: Identification and Dating of Tsunami Deposits in a Far-Field Tropical Setting

“…Paleoseismological records can be derived from ages and heights of uplifted terraces (e.g. Aung et al 2008;Rajendran et al, 2008) and ages and level of vertical movement recorded in coral microatolls (e.g. Sieh et al, 2008;Meltzner et al, 2010) above or near the active subduction zone.…”

Active Convergence of the India‐Burma‐Sunda Plates Revealed by a New Continuous GPS Network

“…The geology records the history of the upper plate. Youthful deformation of anticlines on Sandwip Island, and possibly the Comilla Tract (Figure ) and uplifted marine terraces on the islands of Cheduba and Ramree (Figure ), indicates continued inelastic deformation of continental shelf sediments in the Holocene (Aung et al, ; Brunnschweiler, ). These observations indicate that the active deformation front of the megathrust extends at least to the mouth of the Ganga‐Brahmaputra delta in Bangladesh, presumably accommodated by the mapped fold and thrust belt (Betka et al, ; Maurin & Rangin, ; Nielsen et al, ; Steckler et al, ).…”

Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: Implications for their identification and preservation in the geological record

“…Although the magnitudes of associated tsunamis seem to be restricted by the preferred slip mode and the comparably shallow bathymetry (Gupta & Gahalaut, ), historical reports from 1762 prove that at least large ruptures are capable of generating tsunami inundation in the northern part of Myanmar. The exact magnitude and rupture geometry of the 1762 earthquake is unknown, but it caused widespread uplift and liquefaction (Cummins, ; Aung et al ., ), as well as a tsunami with localized inundation levels of probably <2·5 m close to Sittwe and in Bangladesh (Alam & Dominey‐Howes, ). Tsunami flooding in Myanmar is also supported by numerical models (Fig.…”

“…2A; Okal & Synolakis, 2008). Predecessors of the 1762 event were identified in the form of seismically uplifted coral terraces (Aung et al, 2008). The ages of these terraces suggest a recurrence interval of 500 to 700 years for large ruptures of the Rakhine segment (Wang et al, 2013a); these may also have caused tsunamis along the Rakhine coast.…”