THE 2004-2005 INDONESIAN TSUNAMIS: LESSONS TO A GEOPHYSICIST

As the largest earthquake in the past 40 years, the Sumatra event on 26 December 2004 has brought new insight to the geophysics community in many areas of seismology, plate tectonics, and tsunami science. We review the lessons learned from this event (and the second Sumatra shock on 28 March 2005) in these various disciplines, including the first application of the splitting of the Earth's normal modes to a high-quality set of digital data, and the reassessment of our understanding of the concept of maximum expectable earthquake in a subduction zone, based on the age and kinematics of the subducting plate. We analyse the triggering of the second event through stress transfer, and discuss the probable future repeat of the 1833 earthquake to the South. We present models of the generation of the 2004 tsunami by a dislocation source extending 1200 km north of the epicenter. The 2004 tsunami was recorded by many instruments not specifically designed for this purpose including satellite altimeters, hydroacoustic probes, infrasound receivers and even long-period horizontal seismometers. We discuss the contribution of these technologies to our understanding of the tsunami generation and propagation, as well as mitigation aspects, and examine in detail the reasons for the failure to provide an adequate warning in the far field. We discuss the reasons for the relatively weak tsunami generated by the 2005 event, despite its ranking as the fifth largest earthquake ever recorded. We stress the necessity of self-evacuation in the near field and the primordial importance of education in this respect.