Underground Forces: Deformation Processes in Gravel Deposits

Jun 21, 2010
Geodynamics at work: Deformation bands in the gravel layers of the Eisenstadt-Sopron Basin.

Deformation bands in the gravel layers of the Eisenstadt-Sopron Basin form as a result of heterogeneous displacement in the surrounding sediment. This is caused by gradients in the deformation intensity, which occur both parallel and perpendicular to a fault.

These findings from a project funded by the Austrian Science Fund (FWF) will help scientists to reach a better understanding of both basic geological processes and the formation and structure of oil and water reservoirs.

As impressively demonstrated by the Himalayas and Pacific oceanic trenches, can really get things moving. However, even these dramatic geological manifestations move just a few millimetres or centimetres per year. Other phenomena associated with geological forces, known as deformation bands, are also subject to movement on a similar scale. These bands arise in soft porous rocks, such as sandstone. They occur where coarse-grained rocks are displaced by the shear forces of the overlying or underlying horizons, or undergo a change in volume. In contrast to what is known as a fault, in which the layer of rock ruptures, in the deformation bands, sediment grains are merely fractured or reorganised. The porosity of the rock and, therefore, its permeability to fluids, changes as a result of this process. Deformation bands thus contribute to the formation and structure of oil or water reservoirs. Attaining a better understanding of their effect on the surrounding rock is the aim of a project being carried out at the Department for Geodynamics and Sedimentology at the University of Vienna.

As part of this study, project leader Dr. Ulrike Exner and her team successfully demonstrated that, due to their relatively coarse grain size, deformation bands in gravels in the Eisenstadt-Sopron Basin near Lake Neusiedl on the Austrian-Hungarian border display a gradient in the strain intensity. This gradient runs from the undeformed neighbouring rock to the middle of the deformation band. As Dr. Exner outlines: "The stresses responsible for this act perpendicular of the deformation band. However, we discovered that a displacement gradient also exists parallel to the fault zone. The largest displacement can be measured in the middle of the deformation band. It decreases above and below this point towards the tips of the band." The presence of these two differently oriented displacement gradients causes folding in the surrounding sediment layers.

Dr. Exner explains the further effects of these heterogeneous deformations in the rock as follows: "The surrounding rock horizons begin to deform. This effect is known as reverse drag. In closely-spaced deformation bands, such drags can even overlap. The resulting geometrical patterns become increasingly complex." However, as Dr. Exner also states, models exist that can explain these patterns: "The so-called domino model explains these patterns in terms of the rotation of blocks of rock between the different deformation bands. Because the rock is still soft and the deformation proceeds very slowly, the behaviour of these blocks is ductile and they are easily deformed."

In the deformation bands examined as part of this project, the ratio between the displacement of the layers of rock pushing against each other and the length of the deformation bands is striking. These ratios, which range from 1:100 to 1:10, are unusually large. According to Dr. Exner, this could facilitate the generation of reverse drag.

Despite the fact that the processes studied by Dr. Exner unfold below the surface of the earth, her work is of direct and practical relevance to everyday life above ground: deformation bands mainly form in porous rock which, due to the presence of numerous pores, also acts as a reservoir for oil or water. Deformation bands alter porosity and can therefore influence the extraction of oil or water. Moreover, the relevance of this FWF project also extends to heavenly heights: the calcareous sandstone, also referred to as Leithakalk (Miocene limestone found in Central Europe), from which St. Stephen's Cathedral in Vienna is built, originates from the Eisenstadt-Sopron Basin. Its porosity - and thus also its response to environmental impacts and protective measures - is also influenced by deformation bands.

Explore further: TRMM satellite sees Tropical Storm Phanfone fragmented

More information: Data were presented at the "European Geosciences Union General Assembly 2010", 2 - 7 May in Vienna, Austria.

Provided by Austrian Science Fund

3 /5 (1 vote)
add to favorites email to friend print save as pdf

Related Stories

Atoms under the mantle

Mar 06, 2007

French CNRS scientists have succeeded in modelling the defects of the earth’s mantle responsible for its deformation. These results, obtained using a novel approach which combines numerical calculus and quantum ...

Faulted modeling

Mar 23, 2007

Factoring in crustal strength changes along the San Andreas Fault would improve the predictive models that researchers use to understand the likelihood and intensity of earthquakes there. That's the conclusion from a study ...

Discovery might improve titanium alloys

Oct 20, 2005

Two University of Maryland scientists say they've developed a modification of titanium alloys that will expand their uses and make them safer.

Understanding mysterious continental intraplate earthquakes

Oct 12, 2007

A new volume published by the Geological Society of America sheds light on mysterious earthquakes in the interiors of continents. These earthquakes, like those that occur in the central U.S., are what the book's editors describe ...

Recommended for you

NASA's HS3 looks Hurricane Edouard in the eye

7 hours ago

NASA and NOAA scientists participating in NASA's Hurricane and Severe Storms Sentinel (HS3) mission used their expert skills, combined with a bit of serendipity on Sept. 17, 2014, to guide the remotely piloted ...

Tropical Storm Rachel dwarfed by developing system 90E

12 hours ago

Tropical Storm Rachel is spinning down west of Mexico's Baja California, and another tropical low pressure area developing off the coast of southwestern Mexico dwarfs the tropical storm. NOAA's GOES-West ...

NASA ocean data shows 'climate dance' of plankton

15 hours ago

The greens and blues of the ocean color from NASA satellite data have provided new insights into how climate and ecosystem processes affect the growth cycles of phytoplankton—microscopic aquatic plants ...

Glaciers in the grand canyon of Mars?

16 hours ago

For decades, planetary geologists have speculated that glaciers might once have crept through Valles Marineris, the 2000-mile-long chasm that constitutes the Grand Canyon of Mars. Using satellite images, ...

NASA support key to glacier mapping efforts

16 hours ago

Thanks in part to support from NASA and the National Science Foundation, scientists have produced the first-ever detailed maps of bedrock beneath glaciers in Greenland and Antarctica. This new data will help ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1 / 5 (1) Jun 22, 2010
A recent paper by Prof. Vladimir Shiltsev [Phys. Rev. Lett. 104, 238501 (2010)] shows that sudden shifts underground do impact large particle accelerators, like CERN's Large Hadron Collider.

With kind regards,
Oliver K. Manuel