FLOOD ELEVATION, INUNDATION DISTANCE AND FLOW COMPETENCE OF THE 2004 SUMATRA-ANDAMAN TSUNAMI, AS RECORDED BY TSUNAMI DEPOSITS IN THIRTEEN SHORE-NORMAL PROFILES FROM THE TAMIL NADU COASTLINE, INDIA

摘要

Thirteen shore-normal profiles in South-Hast India have been surveyed for tsunami deposit evidence of run-up height, flow depth, inundation distance, flow competence, and flow direction from the December 26 Sumatra-Andaman tsunami. Mud lines on buildings were surveyed into timed tide level (swash zone) to establish maximum still-water height, which ranged from 2.3 to 4.4 m mean tide level (MTL). Hanging debris and structural damage were used to establish maximum surge heights of 3.9 to 6 m MTL. Differences between maximum surge height and ground surface yielded flow depths of 1.2 to 3.2 m. Landward flow directions, as recorded by vegetation flop-overs, sand ripples, and debris shields averaged 250°N yielding an oblique wave attack of 30-40° in central study area. Maximum inundation distances of gravel, i.e., shore-normal distance from mid-swash zone, ranged from 30 to 60 m. Maximum sand transport ranged from 90 to 400 m in distance from the shoreline. Sand sheet deposits ranged from 1 to 30 cm in thickness, and included internal stratification, rare pebble and shell clasts. Maximum tsunami flood inundation, based on transported flotsam, ranged from 140 to 800 m in shore-normal distance. Flotsam transport exceeded sand transport by between 15 and 50% of maximum inundation distance in nine profiles. These preliminary reconnaissance observations characterize the recent tsunami inundation from low-to-moderate forcing, i.e, maximum still water 2-4 m MTL, in the low-relief settings of the South-East India coastal plain.