Research Highlights

Geologists find traces of ancestral Indian Ocean tsunamis

- Rajendran C.P. and Rajendran K , CEaS

Although written history failed to forewarn of the enormity of the 2004 Indian Ocean tsunami, geologic history tells of two predecessors in the last millennium. The 2004 earthquake and tsunami are marked by sand and coral rubble on beaches, debris left inland along streams, tidal flooding of coastal lowlands that subsided, uplifted coastal terraces, and sand blows from liquefaction. Exposed along the 1300-km-long rupture area, these features aid in identifying previous earthquakes and tsunamis on these same shores. Such evidence attests to tsunamis as ancient as the 2nd and 6th centuries AD. The clues are more abundant for a tsunami in the interval AD 770-1040 both near its northwest Sumatran source area and farther afield, on the east coasts of India and Sri Lanka. A more recent tsunami in AD 1250-1450 is evidenced by deposits on the Andaman and Nicobar Islands as well as shores of Thailand and Indonesia. Such geologic histories of infrequent, ocean wide tsunamis have important implications for hazards on Indian Ocean shores.

C. P. Rajendran, Kusala Rajendran, Vanessa Andrade, and S. Srinivasalu (2013). Ages and relative sizes of pre-2004 tsunamis in the Bay of Bengal inferred from geologic evidence in the Andaman and Nicobar Islands, Jour. Geophys. Res. 118, 1-18, doi:10.1002/jgrb.50122.

Figure: A space-time diagram showing the age range of paleotsunamis