Microzonal mapping a valuable tool for protecting buildings against damage resulting from earthquakes
In countries with as much seismic activity as Greece, a lot can be done to make buildings safe by means of a method known as microzonal studies: a form of research that gives precise instructions to engineers on how to build in specific areas, in each block or neighborhood. There is a growing trend around the world to see these studies as one of the most effective tools in making buildings resistant to earthquakes. Yet because they are expensive and time-consuming, they are not often used in Greece and where they have been carried out, it has been in the absence of any legislative framework, without any precise determination of tasks or evaluation of the result, or even the compulsory implementation of final instructions. After the catastrophic 1999 earthquake in Athens, attention was focused once more on the need for a stricter framework for seismic protection. Unfortunately, not much has been done since then, and little more than scientific debates, isolated measures or wishful thinking. «Earthquakes are here to stay. Even if we manage to predict them with any accuracy – and that is unlikely in the near future – earthquakes will keep occurring. So we need to minimize the consequences,» said Constantine Makropoulos, the head of Athens University’s geology faculty. «As it is impossible to predict earthquakes with any precision, we are trying by means of various studies to have the greatest possible reduction in the effects of an earthquake,» said Giorgos Stavrakakis, director of the Geodynamic Institute and of the new Seismic Risk Evaluation Committee. «If these studies are implemented correctly, earthquake-resistant design procedures will be based on a number of factors. A microzonal study is a complex, multidisciplinary study by seismologists, geologists, geophysicists, soil engineers and civil engineers, among others. It studies the phenomenon of the earthquake from its epicenter right up to where it ends up; in the buildings themselves.» One would expect that in a country with as much seismic activity as Greece, the State would encourage the use of microzonal studies, at least in larger cities and in more high-risk areas. Yet despite commitments by the previous environment and public works minister, this has not happened. The only provision was in housing law 2508/97 providing for compulsory geological studies (just part of the microzonal study), for areas to be included in the town plan. The Seismic Regulations of 2000 require a geological study to be carried out before construction begins on any building with a total volume of more than 4,000 cubic meters. Since there is no real, long-term state plan for microzonal studies, the few that are actually carried out are funded by the Organization for Seismic Protection (OASP) only after the event (such as the destructive quakes in Kalamata, Aigion and Konitsa). Most studies are commissioned by municipalities at their own initiative. «However, they are not required to inform us,» explained OASP geologist Spyros Lalehos. «Two years ago we asked prefectures and research organizations to tell us what kind of studies they had done. The research foundations are slowly sending us replies, but not the prefectures.» Kathimerini talked to professors from geology departments in Athens, Thessaloniki and Patras and civil engineering departments in Athens and Thessaloniki, as well as experts from seismology laboratories and other research organizations. It emerged that over the past 20 years, microzonal studies have been carried out in Ano Liosia, Rendi, Anthoupoli, Peristeri, Thiva, Iraklion, Larissa, Volos, Aigion, Konitsa, Grevena, Kozani (two studies), Karditsa, Loutraki and Corinth. Studies are currently under way in Thessaloniki, Mytilene, Rhodes and Rethymnon. Individual studies (just part of a microzonal study) have been done in many parts of the country. It is unsure, however, whether all the above-mentioned cities have been studied extensively, because the State has not imposed rules as to what such an important multidisciplinary study should involve. Nor do the engineers take them into account where they do exist. «I believe that the whole issue is being mishandled. A number of microzonal studies have been carried out, but everyone means something different by that,» explained Demosthenes Moudrakis, professor of tectonic geology. Between 1996 and 1998, OASP tried to introduce some form of order, by holding a conference and setting up a team of experts who drafted proposals for drawing up microzonal studies. After some disagreements arose, the plan was reviewed and eventually put aside for further review. Between 2000-2001, the Seismic Risk Evaluation Committee took over. A new team of experts arrived at a plan for «comprehensive studies to reduce seismic risk in the built environment.» The final plan, which attempted to determine the role of each member of a scientific team, met with opposition and has been delayed, according to the president of OASP, Vassilis Andrianakis. Combined effort needed For a microzonal map to be made of a particular site, a number of specialized studies need to be made, each of which include more individual studies, involving several disciplines. Seismologists study the seismic activity and determine the seismic acceleration, arriving at an evaluation of the seismic risk in a particular area. Geologists look at the geological and tectonic structure and classify fault lines according to their potential. Geotechnicians and civil engineers evaluate the soil characteristics from the bedrock to the surface, using various methods such as drilling and soil samples. Geophysicists work with geologists and geotechnicians to arrive at a more precise evaluation of the soil, such as hidden fault lines, and its behavior during a quake. Soil engineers or civil engineers determine the seismic acceleration at the surface. They estimate the behavior of a building during a quake at a specific site and decide how it should be designed.