Sedimentary Deposits from the 17 July 2006 Western Java Tsunami, Indonesia: Use of Grain Size Analyses to Assess Tsunami Flow Depth, Speed, and Traction Carpet Characteristics

摘要: The 2006 western Java tsunami deposited a discontinuous sheet of sand up to 20 cm thick, flooded coastal southern depth at least 8 m and inundated 1 km inland. In most places the primarily heavy mineral is normally graded, in some it contains complex internal stratigraphy. Structures within probably record passage two individual waves, point noted eyewitness accounts. We studied deposits detail along flow parallel transect about 750 long, 15 east Cilacap. deposit first becomes discernable from underlying sediment 70 shoreline. From 75 300 inland has been laid down rice paddies, maintains thickness 10–20 cm. Landward thins dramatically, reaching mm by 450 edge deposition (around 700 inland) remains <1 thick. Deposition generally attended inundation—along transect, 40 inundation limit. thicker part indistinguishable that found on beach 3 weeks after event, but (and roughly coinciding with decrease thickness) shifts become more like paddy soil than sand. Grain sizes tend fine upward landward, although overall fining takes place discrete pulses, an initial section inverse grading followed normal grading. inversely graded sections are also density denser grains base, less dense top. show no trends density. high base represents traction carpet flows tsunami. These suggestive shear rates flow. Because grain sorting carpet, landward-fining usually seen masked, lateral changes mean size do landward fining, variation as tapers off. seaward portions would be produced tsunamis lacking carpets.