1 Introduction

The Indian Ocean (Sumatra) tsunami of 26 December 2004 was one of the world’s most destructive natural disasters. Spawned by a magnitude (M w) 9.1 earthquake (third strongest ever instrumentally recorded), the "Boxing Day" tsunami killed approximately 230,000 people in 14 countries around the Indian Ocean. Among the victims were citizens of more than 60 countries, many of them on holiday. The tsunami propagated as far as the North Pacific and North Atlantic (Rabinovich et al. 2006) and was probably the most catastrophic and deadliest tsunami in recorded history.

The devastating 2004 tsunami represents a scientific dividing line. Prior to the monumental event, the term “tsunami” was familiar only to specialists. Within hours of the event, the entire world came to understand the power of tsunami waves. Thousands of new researchers from different fields entered tsunami science, bringing their diverse experience along with new ideas. Various countries from around the globe contributed major funding to tsunami research, enabling the installation of hundreds of new high-precision instruments, the development of new technology, and the establishment of more modern communication systems. As a result, incredible progress has been achieved in tsunami research and operation during the ten years after the 2004 Indian Ocean tsunami.

Tsunami warning and hazard mitigation systems have dramatically improved. The tsunami observational network of coastal tide gauges has been significantly reconstructed, upgraded, and expanded. Tsunami waves began to be monitored in both the deep ocean and from space. A large number of Deep-ocean Assessment and Reporting of Tsunamis (DART) stations have been emplaced in optimized alignment with the subduction zones encircling the entire Pacific Ocean; DARTs are now also deployed in the Indian and Atlantic Oceans. These new, precise instruments have yielded thousands of coastal and hundreds of deep-water, high-quality tsunami records, enabling researchers to refute some previous misconceptions and to improve knowledge significantly about tsunami physics. Modern numerical models, combined with open-ocean DART records, make it possible to forecast tsunami waves for coastal sites with reliable accuracy soon after a major earthquake.

However, despite the recent advances, tsunamis remain a major threat to coastal infrastructure and human life. Destructive tsunami events continue to kill people and create enormous damage. Several catastrophic events occurred in 10 years after the 2004 Indian Ocean (Sumatra) tsunami, including the 2006 Java, 2009 Samoa, 2010 Chile, and 2010 Mentawai tsunamis with hundreds of fatalities per event. The Tohoku (Great East Japan) tsunami of 11 March 2011, which killed almost 20,000 people and destroyed the Fukushima Daiichi nuclear power plant, was a tragic example of a chain of devastating events (Satake et al. 2013a). We can state with some certainty that the number of victims would have been many times higher without existing tsunami mitigation programs and effective tsunami warning services in Japan and other countries.

The present volume was prepared by the Tsunami Commission that was established within the International Union of Geodesy and Geophysics (IUGG) following the 1960 Chile tsunami. The 1960 tsunami, generated by the largest (M w 9.5) instrumentally recorded earthquake, propagated throughout the entire Pacific Ocean, affecting countries located far from the source with 142 fatalities in Japan almost a day later, 61 in Hawaii, and 32 in the Philippines (Igarashi et al. 2011). It became obvious that tsunami investigation and effective tsunami warning is impossible without intensive international cooperation. Since 1960, the Tsunami Commission has held biannual International Tsunami Symposia and published special volumes of selected papers. Several such volumes have been published during the 10 years following the 2004 Sumatra tsunami, including Satake et al. (2007, 2011a, b, 2013a, b) and Cummins et al. (2008, 2009). From this point of view, these volumes can be considered the frontiers of tsunami science and research, as well as a record of continuous progress in tsunami warning and hazard mitigation. Two recent catastrophic tsunamis, the 2010 Chile and 2011 Tohoku, as well as other events that occurred in 2011 and 2012, attracted much attention and revealed significant new information and data, which were published in an extra, inter-session volume (Rabinovich et al. 2014).

This volume is mainly based on papers presented at the 26th International Tsunami Symposium that was held from 25 to 28 September 2013 in Göcek, Turkey and Rhodes, Greece. Altogether, the symposium comprised about 150 presentations. For the first time in history, two countries hosted the tsunami symposium. Also for the first time, two tsunami sessions, one mainly focusing on the tsunami physics and the other focusing on paleotsunami studies, were convened in parallel. At the business meeting of the Tsunami Commission, it was decided to publish selected papers presented at this symposium, as well as other papers on related topics. Volume I comprises the first half contributing 22 papers, which became ready for publication by December 2014. Approximately the same number of papers will be published forthcoming in Volume II.

2 Case Studies

Case studies are an important part of tsunami research that highlight the hazard for specific areas—often areas that have been overlooked for tsunamis. For example, Heidarzadeh and Satake (2015) re-evaluate the source for the 1945 Makran tsunami that struck Oman, Iran, Pakistan, and India. They find that earthquake rupture needs to extend into deep water to explain the tsunami observations. Also from the Indian Ocean, Nentwig et al. (2015) study sedimentary deposits left by the 2004 Indian Ocean tsunami in the Seychelles Islands and find that tsunami sediments caused a change of habitat in mangrove forests on the Islands. In the South Pacific Ocean, the great 2007 Solomon Islands earthquake ruptured across a triple junction leaving behind significant bio- and geo-markers of crust rupture and generated tsunami waves. Wei et al. (2015) developed tsunami inundation models for the Solomon Islands, highlighting the accuracy and efficiency of the tsunameter-derived tsunami source for near-field tsunami impact assessments along a complex archipelago. Murotani et al. (2015) examined forerunner tsunami waves generated immediately after the 2011 Tohoku-Oki earthquake in the Sea of Japan; they found that these waves, recorded both on the west coast of Japan and on Primorye coast of Russia, were caused by the horizontal displacement of the seafloor slope.

The 2012 Haida Gwaii earthquake was the second strongest instrumentally recorded earthquake in Canadian history and generated a sizable tsunami. Fine et al. (2015) use observations of this event, including those from Canada’s deep-ocean cabled observatory, to formulate a detailed source model for this event. The initial model results were used to specify sites of particular interest for post-tsunami field surveys on the coast of Moresby Island (Haida Gwaii), while the field survey observations (Leonard and Bednarski 2014) were used, in turn, to verify the numerical simulations. Deep-ocean measurements are also critical to the study by Heidarzadeh et al. (2015) who examine delays in the observed 2014 Chile tsunami compared to what was predicted. Borrero et al. (2015) systematically examine the tsunami hazard at New Zealand ports from Pacific Rim earthquakes and find that earthquakes off Central America present the largest hazard. Also, Borrero and Goring (2015) specifically examine the tsunamis originating from South American subduction zones, focusing on one harbor (Lyttelton, South Island) in New Zealand.

3 Forecast/Warning Studies

Numerical models that provide real-time forecasting of tsunami amplitudes have been developed, starting even before the 2004 Indian Ocean event. Gica et al. (2015) examine the sensitivity that different types of data collected in real time have on the accuracy of tsunami forecasts and find, intuitively, that direct observations of tsunami waveforms have the biggest impact. In the first of two companion papers, Clement and Reymond (2015) describe new tools to determine the seismic moment and focal mechanism of tsunamigenic earthquakes and to identify anomalous “tsunami earthquakes” for warning systems. In the second paper, Jamelot and Reymond (2015) present two numerical tsunami modelling tools to forecast runup, inundation and flow velocities in French Polynesia. Schindele et al. (2015) describe the tools used by the French Tsunami Warning Center as part of the Northeastern Atlantic and Mediterranean tsunami warning system. From both a scientific and an emergency management perspective, Cassidy (2015) presents an informative comparison of the earthquake that generated the 2004 Indian Ocean event and potential earthquakes and tsunamis along the Cascadia subduction zone.

4 Benchmark and Analytical Studies

Given the critical use of numerical tsunami models to determine hazard and evacuation zones, much emphasis has been placed in recent years on benchmarking models against analytical solutions, laboratory experiments and case studies. Whereas most benchmarks relate to amplitude, runup, and inundation, the study by Arcos and LeVeque (2015) benchmarks the GeoClaw model with respect to current velocities, which have only recently become available in the field. More traditional benchmark exercises are presented by Horrillo et al. (2015) who describe validation of maximum surface amplitude and runup for a number of different tsunami models used to predict inundation for evacuation plans, under the auspices of the U.S. National Tsunami Hazard Mitigation Program. It is important to determine accurately the tsunami response in bays of different configurations. Toward this end, Harris et al. (2015) analytically derive the 1D, nonlinear tsunami response in trapezoidal bays and compare the results with those calculated from a 2D numerical model.

5 Inundation and Structural Studies

New developments have been made in the last 10 years in preparing tsunami inundation maps. For example, Dilmen et al. (2015) use very high-resolution, near-shore bathymetry and topography from multispectral satellite imagery to prepare tsunami inundation maps for the region near Fethiye, Turkey. Ozer et al. (2015) describe and calculate the “hydrodynamic demand” parameter in inundation zones that estimates damage to coastal structures from drag forces during tsunami runup. Within the last 10 years, probabilistic methods have been developed to assess tsunami hazards for engineering purposes. Omira et al. (2015) present a regional probabilistic tsunami hazard assessment for coastlines along the northeast Atlantic Ocean, using in part Bayesian methods to incorporate catalog data. The unique hydrodynamic response of tsunamis as they propagate up into rivers is examined by Tolkova et al. (2015). They find that different rivers for different tsunami events modulate the tsunami in very similar ways.

6 Source and Generation Studies

Volume I of “Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami” wraps up with two papers that provide new examinations on the sources of tsunamis. Hossen et al. (2015) find that Time Reverse Imaging (TRI) used to reconstruct the initial sea-surface displacement for tsunamis obviates many of the assumptions used for traditional, forward modelling of tsunami sources. Stefanakis et al. (2015) examine the effect of uplifting a cylindrical sill during tsunami generation, analogous to the uplift of a seamount. They find that whereas the sill effect reduces wave heights in the far field, there is amplification of wave heights above the sill, owing to partial wave trapping.