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Paleoseismic Records of 1762 and Similar Prior Earthquakes Along the South-Eastern Coast of Bangladesh Dhiman Ranjan Mondal1,2, Cecilia M McHugh3, Richard A Mortlock4, Michael S Steckler5, Leonardo Seeber5, Sharif Mustaque6, Steven Lee Goodbred Jr7, Syed Humayun Akhter6 and Pritam Saha6, (1)CUNY Graduate School and University Center, Earth and Environmental Sciences, New York, NY, United States, (2)CUNY Queens College, School of Earth and Environmental Sciences, Flushing, NY, United States, (3)CUNY Queens College, Flushing, NY, United States, (4)Rutgers University, Piscataway, NJ, United States, (5)Lamont-Doherty Earth Obs, Palisades, NY, United States, (6)University of Dhaka, Dhaka, Bangladesh, (7)Vanderbilt University, Dept Earth and Environmental Sciences, Nashville, TN, United States Abstract Text: The great 1762 Arakan earthquake caused subsidence and uplift along 700km of the Arakan coast, and is thought to derive from a huge megathrust rupture reaching northward onto the southeastern coast of Bangladesh. Paleoseismic investigations were conducted in that area to document effects of that and prior earthquakes. U/Th ages obtained from isochron analysis of uplifted dead coral heads of the Porites species, collected along a south to north transect from the islands east coast reveal at least three growth interruptions caused by abrupt relative sea-level changes within the past 1300 years that we interpret to be associated with megathrust ruptures. The ages show distinct events approximately 250, 900 and 1300 years ago. The youngest of these events corresponds to the 1762 Great Arakan earthquake. The two prior events at ~1100 and 700 AD, suggest an average recurrence interval of 400-600 years. Along the coast of Teknaf, we mapped a ~2m uplifted terrace. Marine shells on top of the terrace dated with C14 at 1695-1791 AD link the uplift to the 1762 Great Arakan earthquake. Based on this evidence and previous work (Wang et al., 2013 and Aung et al., 2008), we estimated the 1762 rupture to be at least 700 km long, from Chebuda Island to the Sitakund anticline encompassing the Teknaf Peninsula. Considering 14 mm/yr convergence rate and 400-600 yrs recurrence interval, this rupture zone has now accumulated elastic deformation to generate a M~8.4 earthquake, close to the M8.7 estimated by Cummins (2007) for the 1762 earthquake. Published recurrence intervals based on C-14 ages along the Myanmar coast ~90 km south of Bangladesh reveal three ruptures within the last 3400 years with an average recurrence interval of 1000-2000 years (Aung et al., 2008). While the 1762 rupture reached across both areas, some of the prior ruptures may be confined to one or the other of these areas, with a smaller magnitude. Our precise U-Th ages provide evidence of recurrence intervals of great megathrust earthquakes along the Arakan subduction zone, which is first to be proposed for historic and prehistoric earthquakes along the coast of Bangladesh. It is critical to constrain the recurrence interval and size of these earthquakes for better hazard assessment, given that three densely populated and structurally unplanned cities are near the rupture zone.
Session Selection: Advances in Sub-Aqueous Paleoseismology: New Insights into Earthquake Recurrence Title: Paleoseismic Records of 1762 and Similar Prior Earthquakes Along the South-Eastern Coast of Bangladesh Submitter's E-mail Address:
[email protected] Preferred Presentation Format: Poster Requested First Presenting Author Presenting Author Dhiman Ranjan Mondal
Primary Email:
[email protected] Phone: 6462384849 Affiliation(s): CUNY Graduate School and University Center Earth and Environmental Sciences New York NY (United States) CUNY Queens College School of Earth and Environmental Sciences Flushing NY (United States)
Second Author Cecilia M McHugh Primary Email:
[email protected] Phone: 7189973322 Affiliation(s): CUNY Queens College Flushing NY (United States)
Third Author Richard A Mortlock Primary Email:
[email protected] Phone: (848)445-3423 Affiliation(s): Rutgers University Piscataway NJ 08854-8066 (United States)
Fourth Author Michael S Steckler Primary Email:
[email protected] Phone: 8453658479 Affiliation(s): Lamont-Doherty Earth Obs Palisades NY 10964-0190 (United States)
Fifth Author Leonardo Seeber Primary Email:
[email protected] Phone: 8453658385 Affiliation(s): Lamont-Doherty Earth Obs Palisades NY 10964-0190 (United States)
Sixth Author Sharif Mustaque Primary Email:
[email protected] Affiliation(s): University of Dhaka Dhaka (Bangladesh)
Seventh Author Steven Lee Goodbred Jr Primary Email:
[email protected] Phone: 6153436424 Affiliation(s): Vanderbilt University Dept Earth and Environmental Sciences Nashville TN 37215 (United States)
Eighth Author Syed Humayun Akhter Primary Email:
[email protected] Affiliation(s): University of Dhaka Dhaka (Bangladesh)
Ninth Author
Ninth Author Pritam Saha Primary Email:
[email protected] Affiliation(s): University of Dhaka Dhaka (Bangladesh)
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