Predicting earthquakes successfully can be a major step to preventing their devastating effect on human settlements. The main method of predicting earthquakes today is to find out where, when and how strongly previous earthquakes occurred. The earthquakes that shook California in 1994 and Kobe, Japan in 1995 both occurred in regions known to be located along fault lines where seismic activity is frequent. But records often do not go back before this century, or do not exist at all for certain regions.
Eric Gilli, a 38-year-old geologist, lecturer at Nice University, director of the private Centre of Karstic Studies (CEK) and speleologist, came up with the idea of searching for traces of earthquakes or fault line movements in caves and caverns. He believes this will allow us "to define the probability of a future earthquake in a given area and to draw up risk-maps".
Gilli plans to search caves in limestone formations for traces of earthquakes over the past 20,000 to 30,000 years. The traces can include large accumulations of fragments of stalactites that have fallen to the cave floor after being dislodged by tremors.
Shakes and Shifts
Since some karstic (limestone) caves are formed along geological faults, they can also reveal information about tectonic movement. Stalactites (which grow from the ceiling) and stalagmites (which are formed on the ground) that no longer face each other indicate, for instance, that the cave roof has shifted in relation to the floor. A break in the direction taken by a stalactite also indicates that the roof’s slant has shifted at some time. Through radio-isotope dating, geologists can reconstruct a cave’s movement during the course of time. These underground studies can show fault lines hidden by soil or vegetation outside.
All these indicators can be measured to estimate the date and intensity of the occurrence, provide an assessment of earthquake risks in regions with no previous records of seismic activity, and allow new earthquake-proof building standards to be introduced.
Aligning the Data
With two other geographers who have considerable caving experience, Gilli began two seismic cave exploration programmes last year. In Costa Rica, Kobe and Los Angeles, all areas of high seismic activity, he is comparing cave damage with earthquakes of known date and intensity. In southern France and Turkey the researchers will try to reconstruct earthquake history from damage observed in caves. The programme continues until June 1997.
"We hope it will allow us to put forward a method for evaluating the risk of earthquakes in a large number of regions where there is no historical data," he says.
Gilli’s doctoral thesis in geology (after a master’s in geography) was on the formation and stability of large underground cavities. A project based on this study earned him an Honourable Mention in the 1987 Rolex Awards for Enterprise. Lack of funds kept him from carrying out the project until 1993, but he was then finally able to travel to the Malaysian state of Sarawak to fulfil his dream of photographing the world’s largest underground chamber to establish an accurate picture of its morphology and structure.
Caves Capture Evidence
Among other innovative techniques, Gilli is also investigating a cheaper alternative to carbon-dating of fixing the age of material found in caves, using the rings found in a disrupted stalactite or stalagmite. His studies could help clarify earth’s history going back a million years or more and lead to the creation of a new branch of earthquake science.
"Caves are very good recorders of natural phenomena. In the same way that the underground environment has preserved prehistoric human records (paintings, bones, tools) for thousands of years, they have also preserved traces of many earth movements," says Gilli.
Published in 1996