Tales set in Stone: learning from ancient earthquakes
Over 335 projects in about 150 countries with contributions of thousands of Earth scientists attest to the scientific and applied quality of theInternational Geoscience Programme (IGCP) since its inception in 1972. Now, 40 years later, there are many stories to tell and the IGCP has decided to celebrate with a publication of some of these Tales set in Stone. In the weeks leading up to the official celebration, we will be using a selection of stories to introduce the 5 major themes of the IGCP: Earth Resources, Global Change, Geohazards, Hydrogeology and Deep Earth.
One such tale is that of IGCP project 567 on ancient earthquakes, what they can tell us about our past, and how we can learn from them to prepare for the future.
Damaging earthquakes along faults typically recur at intervals of centuries to millennia. But the instruments that can register them have only been available for about a hundred years. To reduce the threat from earthquakes, we need a longer record of them than that which has been provided by such instruments. Archaeological evidence has the potential to reveal earthquake activity over millennial time spans, especially when integrated with historical documents and geological evidence. The international geosciences programme (IGCP) project 567 on earthquake archaeology is intended to demonstrate that archaeological evidence can make a valuable contribution to long-term seismic-hazard assessments in earthquake-prone regions where there is a long and lasting cultural heritage.
Although archaeoseismology (the study of ancient earthquakes through indicators left in the archaeological record) has a lineage that extends back to the pioneering excavations of Schliemann at Troy, Evans at Knossos and Schaeffer at Ugarit in the late 19th and early 20th centuries, it is essentially a young and burgeoning discipline that has met with much reservation from some earthquake scientists. Many of them question whether cultural phenomena, including destruction layers, cultural-piercing features (man-made structures displaced by surface rupturing, e.g. viaducts), structural damage to buildings, indications of repairs, historical accounts and myths can be reliably used as earthquake indicators.
The problem seismic-hazard practitioners face, however, is that the instrumental record of earthquakes is too short and the historical record too incomplete. Historical catalogues record only a tiny proportion of the sizeable shocks that have struck a region over centuries and millennia; such missing ‘populations’ in the earthquake records temper reliable seismic-hazard assessments, but the archaeological record can bolster and augment that historical archive. What is more, in extending the earthquake record beyond the written sources, archaeoseismology serves as a bridge between instrumental and historical seismology, on the one hand, and palaeoseismology and earthquake geology, on the other. Only the integration of all potential evidence for past earthquakes enables us to advance our understanding of the complex earthquake history of a region. Archaeoseismology has the potential to be a legitimate and complementary source of seismichazard information.
What holds archaeoseismology back from being a mature scientific discipline is its lack of a rigorous and transparent methodology. To date, many practitioners have proposed procedural schemes for archaeoseismological investigations but, in most cases, these schemes are designed from within a single scientific discipline, revealing archaeoseismology’s principal hubris, namely the interdisciplinary nature of the evidence that confronts it. Archaeoseismology calls upon the expertise of historians, anthropologists, archaeologists, geologists, seismologists, geophysicists, architects and structural engineers. Integrating the principles and practices of such a wide range of disciplines is archaeoseismology’s greatest challenge and its foremost attraction.
IGCP 567 took up this challenge not only by bringing together the world’s principal practitioners in archaeoseismology, but also by expanding this nucleus with young and emerging scientists, and by integrating our activities with the practitioners in palaeoseismology as well as with historical and instrumental seismology. Together with our colleagues of the INQUA (International Union for Quaternary Research) focus area group on palaeoseismology and active tectonics, IGCP 567 started a new tradition of joint field workshops. The initial workshop was organized in 2009 at the archaeological site of Baelo Claudia in southern Spain; the second took place in 2011 in Corinth, Greece; a third is planned for 2012 in Morelia, Mexico; and a fourth in 2013 in Aachen, Germany.
The confrontation of ideas at these workshops has definitively advanced the discipline to a level that archaeoseismological evidence is now considered as a complementary source of earthquake data in the whole range of approaches in earthquake science. During the period of IGCP 567, the archaeoseismological principles and practices have further matured in pursuing an intimate relationship with other disciplines of earthquake science. These integration efforts are clearly expressed in published work, offering a taste of the complexity confronting archaeoseismologists. A new textbook on archaeoseismology is planned for 2012, guaranteeing a lasting legacy for IGCP 567. The strength of this new community (active in the social media as paleoseismicity.org) has also increased the visibility of our work, not only in the scientific community but also across a wide public audience. IGCP 567 turned out to be an incentive for an active engagement from our community in geosciences communication and outreach activities for local communities at each of the field workshops, but also for various international media.
There is a wider remit for our activities, because they clearly have important societal benefits. As illustrated by the collapse of the magnificent antique citadel at Bam, the largest sun dried bricks (adobe) building in the world and a World Heritage Site, during the devastating earthquake that struck this ancient Iranian city, cultural heritage sites themselves are threatened by earthquake destruction.
Clearly, there is a growing need to understand how ancient structures and monuments respond to faulting and ground shaking. Our work also contributes to our understanding of ancient history, elucidating why some cities were abandoned or why mature societies suffered decline, and confronting the enduring attraction of fault lines in luring peoples, ancient and modern, to settle along persistent danger zones. By highlighting how their ancestors coped with earthquakes, archaeoseismology should play a key role in fostering better earthquake preparedness in modern communities that are equally threatened.
In this respect, the legacy of IGCP 567 will be a strong community of practitioners who are well disposed towards archaeoseismology, advocating a holistic approach that will eventually contribute to the establishment of an essential earthquake culture in the Alpine-Himalayan region, occasionally confronted with the inevitable earthquake catastrophe.
One of the project members, Iain Stewart, will make a presentation during the IGCP 40th Anniversary Celebration on 22 February 2012 at UNESCO headquarters in Paris.
By: Manuel Sintubin, Department of Earth & Environmental Sciences, Katholieke Universiteit Leuven, Belgium; Iain Stewart, School of Geography, Earth and Environmental Sciences, Plymouth University, UK; Tina M. Niemi, Department of Geosciences, University of Missouri-Kansas City, US; Erhan Altunel, Department of Geological Engineering, Eskişehir Osmangazi Üniversitesi, Turkey.
Extract taken from Tales set in Stone – 40 Years of the International Geoscience Programme IGCP, published in 2012 by the United Nations Educational, Scientific and Cultural Organization