Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earthquakes and tectonics in Pamir Tien Shan

28.08.2013
Real time observation of shear waves on the Earth's surface, first direct observation of subducting continental crust during the collision of two continents

Earthquake damage to buildings is mainly due to the existing shear waves which transfer their energy during an earthquake to the houses. These shear waves are significantly influenced by the underground and the topography of the surrounding area.


Landslide of Papan, South Kirisistan


Subduction Pamir / Eurasien

Detailed knowledge of the landform and the near-surface underground structure is, therefore, an important prerequisite for a local seismic hazard assessment and for the evaluation of the ground-effect, which can strongly modify and increase local ground motion.

As described in the latest issue of Geophysical Journal International, a team of scientists from the GFZ German Research Center for Geosciences could show that it is possible to map complex shear wave velocity structures almost in real time by means of a newly developed tomgraphic approach.

The method is based on ambient seismic noise recordings and analyses. "We use small, hardly noticeable amplitude ground motions as well as anthropogenic ground vibrations", Marco Pilz, a scientist at GFZ, explains. "With the help of these small signals we can obtain detailed images of the shallow seismic velocity structure". In particular, images and velocity changes in the underground due to earthquakes and landslides can be obtained in almost real time.

"What is new about our method is the direct calculation of the shear wave velocity. Moreover, we are working on a local, small-scale level -- compared to many other studies", Marco Pilz continues.

This method has already been successfully applied: Many regions of Central Asia are threatened by landslides. Since the shear wave velocity usually drops significantly before a landslide slip this technique offers the chance to monitor changes in landslide prone areas almost in real time.

Further application can be used in earthquake research. The authors were able to map the detailed structure of a section of the Issyk-Ata fault, Kyrgyzstan, which runs along the southern border of the capital city, Bishkek, with a population of approx. 900.000 inhabitants. They showed that close to the surface of the mapped section a splitting into two different small fault branches can be observed. This can influence the pace of expansion or also an eventual halting of the propagation on the main fault.

Central Asia is extensively seismically endangered; the accompanying processes and risks are investigated by the Central-Asian Institute of Applied Geosciences (CAIAG) in Bishkek, a joint institution established by the GFZ and the Kyrgyz government.

Why do these earthquakes occur?

The Pamir and Tien Shan are the result of the crash of two continental plates: the collision of India and Eurasia causes the high mountain ranges. This process is still ongoing today and causes breaking of the Earths crust, of which earthquakes are the consequence.

A second group of GFZ-scientists has investigated together with colleagues from Tajikistan and CAIAG the tectonic process of collision in this region. They were, for the first time, able to image continental crust descending into the Earth's mantle. In the scientific journal Earth and Planetary Sciences Letters the scientists report that this subduction of continental crust has, to date, never been directly observed. To make their images, the scientists applied a special seismological method (so-called receiver function-analysis) on seismograms that had been collected in a two years long field experiment in the Tien Shan-Pamir-Hindu Kush area. Here, the collision of the Indian and Eurasian plates presents an extreme dimension.

"These extreme conditions cause the Eurasian lower crust to subduct into the Earth's mantle", explains Felix Schneider from the GFZ German Research Centre for Geosciences." Such a subduction can normally be observed during the collision of ocean crust with continental crust, as the ocean floors are heavier than continental rock."

Findings at the surface of metamorphic rocks that must have arisen from ultra-high pressures deep in the Earth's mantle also provide evidence for subduction of continental crust in the Pamir region. Furthermore, the question arises, how the occurrence of numerous earthquakes at unusual depths of down to 300 km in the upper mantel can be explained. Through the observation of the subducting part of the Eurasian lower crust, this puzzle could, however, be solved.

M. Pilz, S. Parolai, D. Bindi, "Three-dimensional passive imaging of complex seismic fault systems: evidence of surface traces of the Issyk-Ata fault (Kyrgyzstan)", Geophysical Journal International, September 2013, 194(3), 1955-1965, doi:10.1093/gji/ggt214

Schneider, F. M.; Yuan, X.; Schurr, B.; Mechie, J.; Sippl, C.; Haberland, C.; Minaev, V.; Oimahmadov, I.; Gadoev, M.; Radjabov, N.; Abdybachaev, U.; Orunbaev, S.; Negmatullaev, S. (2013): "Seismic imaging of subducting continental lower crust beneath the Pamir", Earth and Planetary Science Letters, Volume 375, August 2013, S. 101-112, doi: 10.1016/j.epsl.2013.05.015

Pictures in printable resolution can be found here:

http://www.gfz-potsdam.de/portal/gfz/Public+Relations/Ressourcen-Images/130826_Hangrutsch

http://www.gfz-potsdam.de/portal/gfz/Public+Relations/Ressourcen-Images/130826_Subduktion_Pamir

F. Ossing | EurekAlert!
Further information:
http://www.gfz-potsdam.de

More articles from Earth Sciences:

nachricht Northern oceans pumped CO2 into the atmosphere
27.03.2017 | CAGE - Center for Arctic Gas Hydrate, Climate and Environment

nachricht Weather extremes: Humans likely influence giant airstreams
27.03.2017 | Potsdam-Institut für Klimafolgenforschung

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Northern oceans pumped CO2 into the atmosphere

27.03.2017 | Earth Sciences

Fingerprint' technique spots frog populations at risk from pollution

27.03.2017 | Life Sciences

Big data approach to predict protein structure

27.03.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>