HR: 0800h
AN: OS31A-0156    [Abstracts]
TI: Sedimentological characteristics of the July 17, 2006 tsunami in South Java
AU: Piepenbreier, J
EM: j.piepen@gmx.de
AF: Geologisch-Palaeontologisches Institut, Muenster University, Muenster, 48149, Germany
AU: * Bahlburg, H
EM: bahlbur@uni-muenster.de
AF: Geologisch-Palaeontologisches Institut, Muenster University, Muenster, 48149, Germany
AU: Spiske, M
EM: micha.spiske@web.de
AF: Geologisch-Palaeontologisches Institut, Muenster University, Muenster, 48149, Germany
AU: Amijaya, H
EM: hamijaya@ugm.ac.id
AF: Department of Geological Engineering, Gadjah Mada University, Yogyakarta, 55281, Indonesia
AU: Weiss, R
EM: Robert.Weiss@noaa.gov
AF: JISAO, University of Washington - NOAA Center for Tsunami Research, 7600 Sand Point Way NE, Seattle, WA 98115, United States
AB: With the help of tsunami deposits, tsunami run-up characteristics and tsunami depositional processes can be inferred in order to understand tsunami as a geological process, but also to recognise tsunami deposits within sedimentary deposits of different sedimentary environments. Unique features of such deposits have not been identified to distinguish them from, for example, storm or other deposits indicating high-energy regimes. The 17 July 2006 tsunami was caused 200 km off the south coast of Java by a ca. 10 km deep Mw 7.8 earthquake at 15:19 local time and struck the coast 20 minutes later. Depending on the geometry of coast and beaches, run- up heights exceeded 20 m at headlands, and were significantly lower, less than 2 m, along many straight beaches. We measured the maximum run-up distance of 700 m at Bunton Beach near Cilacap. Quasi-linear debris accumulations document up to three subsequent waves of decreasing inundation and run-up. We surveyed beaches along the central south coast of Java between Pangandaran and Parangtritis south of Yogyakarta and sampled the tsunami deposits. The analysed deposits taper landward and often have erosive bases. Bottom layers may contain soil rip-up clasts incorporated from inundated agricultural fields. Sedimentary structures include small current ripples documenting backwash flow in morphological depressions. Deposits consist of up to 5 layers of medium and fine sand which display a weakly developed fining inland trend. Individual layers may be graded. Deconvolution of grain-size distributions revealed that the most deposits were derived from at least two well sorted, normal grain populations, the modes of which differ by up to 1 phi unit. Both grain populations were most likely derived from well sorted beach and near shore sands. Benthic formaminifera deposited with the sands indicate shallow marine environments of sediment entrainment.
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 1850 Overland flow
DE: 1861 Sedimentation (4863)
DE: 3022 Marine sediments: processes and transport
DE: 4564 Tsunamis and storm surges
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting