Numerous conurbations all over the world such as Istanbul, Tokyo or Mexico City are exposed to a high earthquake risk. In the Turkish metropolis for example scientists are expecting a large earthquake in future due to its proximity to the North Anatolian Fault, where the Eurasian Plate shifts against the Anatolian Plate. In Istanbul and other cities technical solutions are being sought with the SOSEWIN sensor early warning system in association with other research projects in order to record earthquakes quickly and to avoid or at least limit catastrophic damage with rapid protection measures.
Earthquakes cannot be predicted with today’s level of knowledge, but can be quickly identified. Knowledge of the different travel times of earthquake waves is used with early warning systems; however, the room for manoeuvre for protective measures is very small, as there are only a few seconds between the arrival of the low-amplitude compression wave (P or primary wave) and the following destructive shear wave (S or secondary wave).
Nevertheless, during this time at least technical facilities such as power lines and gas pipelines can be shut down, trains halted, bridges closed and dangerous industrial processes stopped. Compared with the consequential damage, generally caused by fires, the damage due to the actual earth vibration is only low.
High hazard potential in Istanbul
With roughly 14 million inhabitants, Istanbul is Turkey’s most populous city and accounts for some 50 per cent of the country’s economic performance. Earthquake activity along the North Anatolian Fault since 1939 shows a series of severe earthquakes migrating westwards from eastern Turkey towards Istanbul. The last earthquake occurred in 1999, only some 100 kilometres east of Istanbul near the city of Izmit. Along the section of the Sea of Marmara south of Istanbul there followed a long period without a large earthquake, which makes an earthquake with a possible magnitude of 7 probable. However, due to the very complex fault system neither the final intensity of such an earthquake nor the location of the epicentre or the possible extent of the fracture can be predicted.
For Istanbul the IRREWS observation network (Istanbul Earthquake Rapid Response and Early Warning System) was constructed within the city area. This comprises ten so-called real-time strong-motion stations along the coast and more than 100 strong-motion stations inside buildings. The real-time stations are installed in the north of the North Anatolian Fault. If three neighbouring stations report a tremor, the central office of the Turkish seismological agency decides whether an alarm situation exists.
By contrast, the devices installed inside buildings are mainly used to record very strong ground movements in order to determine their connection with possible construction damage.
Since summer 2008 this system has been extended to include a decentralized, self-organizing early warning system developed at the GeoForschungsZentrum (German Research Centre for Geosciences) in Potsdam. SOSEWIN (Self-Organizing Seismic Early Warning Information Network) is the prototype of a sensor network communicating wirelessly via WLAN. It guarantees real-time capable transmission of large quantities of pre-processed data.
Comprehensive early warning system for thousands of buildings
Text: Dr. Claus Milkereit