HR: 1400h
AN: T43B-04    [Abstracts]
TI: Searching for Pre-2004 Tsunami Deposits in Thailand
AU: * Tuttle, M
EM: mptuttle@earthlink.net
AF: M. Tuttle and Associates, 128 Tibbetts Lane, Georgetown, ME 04548, United States
AU: Alam, S
AF: University of Alberta, Geoenvironmental Engineering, Edmonton, AL T6G 2W2, Canada
AU: Atwater, B
AF: U.S. Geological Survey, University of Washington, Box 351310, Seattle, WA 98195, United States
AU: Charoentitirat, T
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Charusiri, P
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Choowong, M
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Fernando, S
AF: Geological Survey and Mines Bureau, Senanayake Building, No. 4, Galle Road, Dehiwala, Sri Lanka
AU: Jankaew, K
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Jittanoon, V
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Kongko, W
AF: Agency for the Assessment and Application of Technology, Grafika No. 2, Yogyakarta, 55281, Indonesia
AU: Maxcia, C
AF: Asian Institute of Technology, School of Engineering and Technology, Phatumthani, 12120, Thailand
AU: Pailoplee, S
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Phantuwongraj, S
AF: Chulalongkorn University, Department of Geology, Bangkok, 10330, Thailand
AU: Rajendran, K
AF: Centre for Earth Science Studies, Akkulam, Trivandrum, 695031, India
AU: Rhodes, B
AF: California State University, Department of Geological Sciences, Fullerton, CA 92831, United States
AU: Srichan, N
AF: Chiang Mai University, Department of Geological Sciences, Chiang Mai, 50200, Thailand
AU: Tejakusuma, I
AF: Agency for the Assessment and Application of Technology, M.H. Thamrin No. 8, Jakarta, 10340, Indonesia
AU: Yulianto, E
AF: Indonesian Institute of Sciences, Sangkuriang, Bandung, 40135, Indonesia
AB: We found only one candidate for a pre-2004 tsunami deposit during a ten-day search in July 2006 of four coastal sites in Phangnga Province. Although our initial field effort was limited, the paucity of pre-2004 tsunami deposits suggests that either there have been few Late Holocene tsunamis like the 2004 event or that the identification of paleotsunami deposits will be challenging in this region. Our investigations at Ban Bang Neang, Ban Lang Ong, Ban Nauk Nai, and Khlong Phru Sai involved examining soils and sediments 30 to 250 cm below the surface in cutbank exposures, gouge-core samples, and excavations. We targeted swales between beach ridges in areas undisturbed by tin mining and where tsunami deposits might have accumulated and been preserved. As shown in previous studies, the deposits of the 2004 tsunami extend as much as 1.5 km inland, thin over high ground, and thicken in swales. The deposits are composed of 1 to 4 beds, ranging from coarse to very fine sand, that commonly fine upward and locally contain parallel laminations. Where estuaries are relatively unprotected by mangroves, the 2004 tsunami deposits extend farther inland. Where mangroves fringe estuaries for 100s of meters, the deposits are concentrated in areas of mangrove damage. Crabs have already destroyed much of the tsunami deposits by mixing it with underlying peaty soil. At Ban Nauk Nai, we found a candidate for a pre-2004 tsunami deposit about 1.1 km inland at the back edge of the coastal plain adjacent to a steep hillslope. The deposit, identified over a distance of 60 meters, consists of a 10-cm-thick, silty, fining-upward coarse to fine sand about 25 cm below the bottom of a shallow pond and the adjoining area. In the same area, the overlying 6 to 13- cm-thick 2004 tsunami deposit consists of a normally graded fine to very fine sand. At the other sites, we found coarse, medium, and fine sand beds typical of coastal plain beach deposits. Although tsunami deposits may occur within the beach deposits, we were not able to identify any with confidence. In future searches, it may be beneficial to target natural ponds near upland areas where accumulation of organics and fines may help to separate tsunami deposits from other sandy deposits. Our findings suggest that the apparent scarcity of pre- 2004 tsunami deposits in Phangnga Province may be due in part to extensive placer mining of the coastal plain, bioturbation of mangrove soils, and difficulty in distinguishing tsunami from beach deposits.
DE: 8158 Plate motions: present and recent (3040)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Joint Assembly