Introduction to "Sixty Years of Modern Tsunami Science, Volume 2: Challenges".

Fifteen papers are included in this PAGEOPH topical issue "Sixty Years of Modern Tsunami Science, Volume 2: Challenges." The issue starts with a general introduction, and then briefly summarizes all contributions, first papers addressing general topics, and then articles grouped on a regional basis: Northern Pacific, Southeast Pacific, Southwest Pacific and Indonesia, and Mediterranean regions.

The quest for wisdom: lessons from 17 tsunamis, 2004-2014.

Since the catastrophic Sumatra-Andaman tsunami took place in 2004, 16 other tsunamis have resulted in significant damage and 14 in casualties. We review the fundamental changes that have affected our command of tsunami issues as scientists, engineers and decision-makers, in the quest for improved wisdom in this respect. While several scientific paradigms have had to be altered or abandoned, new algorithms, e.g. the W seismic phase and real-time processing of fast-arriving seismic P waves, give us more powerful tools to estimate in real time the tsunamigenic character of an earthquake. We assign to each event a 'wisdom index' based on the warning issued (or not) during the event, and on the response of the population. While this approach is admittedly subjective, it clearly shows several robust trends: (i) we have made significant progress in our command of far-field warning, with only three casualties in the past 10 years; (ii) self-evacuation by educated populations in the near field is a key element of successful tsunami mitigation; (iii) there remains a significant cacophony between the scientific community and decision-makers in industry and government as documented during the 2010 Maule and 2011 Tohoku events; and (iv) the so-called 'tsunami earthquakes' generating larger tsunamis than expected from the size of their seismic source persist as a fundamental challenge, despite scientific progress towards characterizing these events in real time.

Seismology: speed and size of the Sumatra earthquake.

Our seismological results reveal that Indonesia's devastating Sumatra-Andaman earthquake on 26 December 2004 was 2.5 times larger than initial reports suggested--second only to the 1960 Chilean earthquake in recorded magnitude. They indicate that it slowly released its energy by slip along a 1,200-km fault, generating a long rupture that contributed to the subsequent tsunami. Now that the entire rupture zone has slipped, the strain accumulated from the subduction of the Indian plate beneath the Burma microplate has been released, and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary, although large earthquakes on segments to the south still present a threat.