Large earthquakes along the North Anatolian Fault Zone increase in magnitude towards the East
Geoscientists and natural disaster management experts are well aware of the risk prevailing in the megacity of Istanbul: The Istanbul metropolitan region faces a high probability for a large earthquake in the near future. The question is: how large can such an earthquake be?
Aerial view of Western Istanbul. The western branch of the North Anatolian Fault Zone runs along the sea bottom of the Marmara Sea (left; photo: M. Bohnhoff, GFZ)
Scientists from the GFZ German Research Centre for Geosciences together with a colleague from the University of Southern California have examined the earthquake maxima along the North Anatolian Fault Zone and came to the astonishing conclusion that mega quakes of magnitude M8 are exclusively to be expected in the east of this earthquake region. On the other hand the maximum earthquake magnitude to be expected in northwestern Turkey including the Istanbul-Marmara region does not exceed M7.5.
Seismologist, Marco Bohnhoff, from the GFZ explains: "We have compiled a new catalogue on historical seismicity for the North Anatolian Fault Zone (NAFZ) dating back to 300 years BC, thus, covering a time period of 2300 years. It is interesting to notice that in the North West of Turkey an earthquake with a magnitude larger than 7.5 has never been observed. On the other hand in eastern Turkey magnitudes of up to M8 are well documented."
The observations can be explained by the age of the fault zone. The NAFZ extends through northern Turkey along more than 900 km from the northern Aegean Sea almost towards the Caucasus. The fault reflects the tectonic boundary between the Anatolian plate and the Eurasian plate in the North.
The Anatolian plate and with it the whole country of Turkey, moves towards the west and hereby interlocks with the Eurasian plate. The plate movement results in an accumulation of stress along the plate boundary that is released in large earthquakes with recurrence periods of several hundreds of years.
The just published new catalogue of historical earthquakes, together with further key parameters such as age, cumulative fault offset, slip rates and maximum length of coherent fault segments reveal a logical explanation.
Geoscientist Bohnhoff: "We were able to demonstrate that the smaller earthquake magnitudes in the west are closely linked to the earlier stage in fault-zone evolution there with an approx. age of eight million years. In comparison the eastern part of the NAFZ with an age of twelve to thirteen million years, is older and more mature. The largest M8 earthquakes solely occur along the older eastern part that also has longer consistent segments".
This is due to the fact that continental transform faults such as the NAFZ have a life cycle. The rock does not fracture along the whole fault zone all at once but rather in sub-segments. In the run of millions of years some of these segments coalesce due to repeated activation during earthquakes.
Thus, due to the older age in the east these longer uniform sections are capable of generating larger ruptures and, therefore, larger earthquakes can be found in the east as compared to the west where the segments are still comparatively small and have not coalesced.
For Istanbul this implies that: Earthquakes as large as M8 are not expected there before further fault evolution that may take several millennia. This is important to estimate upper bounds for the seismic hazard and risk of the city.
This, however, by no means reduces the general seismic hazard for the metropolitan region since the NAFZ is located only 20 km away from the historic city center below the seafloor of the Marmara Sea where an up to M 7.5 earthquake can cause a great threat to the local population and infrastructure.
The results of the newly published study are relevant for the estimation of expected maximum magnitudes in highly populated regions, as well as for the determination of seismic hazards and the accompanying risks and, last but not least, they provide important baselines for adapting building codes.
Marco Bohnhoff, Patricia Martínez-Garzón, Fatih Bulut, Eva Stierle, Yehuda Ben-Zion: “Maximum earthquake magnitudes along different sections of the North Anatolian fault zone”, Tectonophysics, ++.03.2016, DOI: 10.1016/j.tecto.2016.02.028
Dipl.Met. Franz Ossing | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz
Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
18.07.2018 | Life Sciences
18.07.2018 | Materials Sciences
18.07.2018 | Health and Medicine