Structural Geology

1. 
ADAMA SCIENCE AND TECHNOLOGY UNIVERSITY
SCHOOL OF APPLIED NATURAL SCIENCE
DEPARTMENT OF GEOLOGY (MSC)
Advanced Structural Geology and Tectonic Assignment
Name: Didha Diriba
ID: PGR/28044/15
SUMMITTED TO: DR. MELESE A.

2. 1.Briefly discusses the methods how to
collect structural data sets and include also
the advantage and disadvantage of each
methods.
The methods to collect structural data sets are:-
Field data
Remote sensing and geodesy
DEM, GIS and Google Earth
Seismic data
Experimental data
Numerical modeling
Organizing the data, etc.

3. It is hard to overemphasize the importance of traditional field
observations of deformed rocks and their structures.
Rocks contain more information than we will ever be able to
extract from them, and the success of any physical or numerical
model relies on the accuracy of observation of rock structures in
the field. Direct contact with rocks and structures that have not
been filtered or interpreted by people or computers is invaluable.
Unfortunately, our ability to make objective observations is
limited. What we have learned and seen in the past strongly
influences our visual impressions of deformed rocks.
Numerical, experimental and remotely acquired data sets are
important, but should always be based on field observations.
Field data

4. In the field of geotectonic, InSAR (Interferometric
Synthetic Aperture Radar) is a useful remote sensing
technique that uses radar satellite images. Beams of
radar waves are constantly sent toward the Earth, and
an image is generated based on the returned
information.
GPS data in general are an important source of data
that can be retrieved from GPS satellites to measure
plate movements.
Remote sensing and geodesy

5. By means of GIS we can combine field observations, various
geologic maps, aerial photos, satellite images, gravity data,
magnetic data, typically together with a digital elevation
model, and perform a variety of mathematical and statistical
calculations.
A digital elevation model (DEM) is a digital representation of
the topography or shape of a surface, typically the surface of
the Earth, but a DEM can be made for any geologic surface or
interface that can be mapped in three dimensions.
The detailed data available from Google Earth and related
sources of digital data have taken the mapping of faults,
lithological contacts, foliations and more to a new level, both
in terms of efficiency and accuracy.
DEM, GIS and Google Earth

6. Continu..
Its disadvantages are:-
Its tools are expensive regarding to cost
It requires efficient processor and higher storage
space
Learning curve on GIS software can be long

7. Some seismic data are collected for purely academic
purposes, but the vast majority of seismic data
acquisition is motivated by exploration for petroleum
and gas. Most seismic data are thus from rift basins
and continental margins.
Acquisition of seismic data is, by its nature, a special
type of remote sensing (acoustic), although always
treated separately in the geo-community. Marine
seismic reflection data are collected by boat, where a
sound source (air gun) generates sound waves that
penetrate the crustal layers under the sea bottom.
 Seismic data

8. Buckle folding, shear folding, reverse, normal and
strike-slip faulting, fault populations, fault
reactivation, porphyroclast rotation, diapirism and
boudinage are only some of the processes and
structures that have been modeled in the laboratory.
The traditional way of modeling geologic structures
is by filling a box with clay, sand, plaster, silicone
putty, honey and other media and applying extension,
contraction, simple shear or some other deformation.
A ring shear apparatus is used when large amounts of
shear are required.
Experimental data

9. Numerical modeling
Numerical modeling of geologic processes has
become increasingly simple with the development of
increasingly faster computers.
The models may range from micro scale, for instance
dealing with mineral grain deformation, to the
deformation of the entire lithosphere.
However, nature is complex, and when the degree of
complexity is increased, even the fastest
supercomputer at some point reaches its physical
limitations.(drawback)

10. Organizing the data
Once collected, geologic data need to be analyzed.
Structural field data represent a special source of data
because they directly relate to the product of natural
deformation in all its purity and complexity.
Because of the vastness of information contained in a
field area or outcrop, the field geologist is faced with
the challenge of sorting out the information that is
relevant to the problem in question. Collecting too
much data slows down both collection and analyses of
the data(drawback)

11. Other data sources
There is a long list of other data sources that can be of
use in structural analysis.
Gravimetric and magnetic data can be used to map
large-scale faults and fault patterns in sedimentary
basins, covered crust and subsea oceanic crust.
Magnetic anisotropy as measured from oriented hand
samples can be related to finite strain.
However, nature is complex, and when the degree of
complexity is increased, even the fastest
supercomputer at some point reaches its physical
limitations.

12. Organizing the data
Once collected, geologic data need to be analyzed.
Structural field data represent a special source of data
because they directly relate to the product of natural
deformation in all its purity and complexity.
Because of the vastness of information contained in a
field area or outcrop, the field geologist is faced with
the challenge of sorting out the information that is
relevant to the problem in question. Collecting too
much data slows down both collection and analyses
of the data. At the same time an incomplete data set
prevents the geologist from reaching sound and
statistically significant conclusions.(drawback)

13. 2. A cylindrical sample is
subjected to axial
compression:
Vertical axial compressive
stress (σa) parallel to the
length of the core is taken
to higher level. Using the
Mohr Stress diagram,
calculate the values of
normal stress and shear
stress.

14. Solution
From the given structure our maximum sigma will be σ1 which is
unplaying down word from Y-axis (1500 Pa). The other one is σ3 which is
give as (500 Pa).
We are asked to calculate normal stress and shear stress.
The formula will be

15. Mohr stress diagram will be

16. Cont…
σN = σ1+ σ3/2 + σ1- σ3/2 *cos2Ѳ
σN =1500 Pa+500 Pa/2 + 1500 Pa- 500 Pa/2 *cos(100)
σN = 1000 Pa +500 cos(100)
σN =913.2 Pa (Normal stress)
σs= σ1- σ3/2 sin2Ѳ
σs= 1500 Pa -500/2 Pa* sin(100)
σs=500 *sin(100)
σs= 492.4 Pa (Shear stress)

17. 3. A cylindrical sample
is subjected to axial
tension:
Horizontal axial
extensional stress (σa)
orthogonal to the
length of the core is
taken to higher level.
Using the Mohr Stress
diagram, calculate the
values of normal
stress and shear stress.

18. Solution
The same formula applied for this too.
The difference between them is value of Sigma and means of tension and
compression. In this question we have σ3= -2000 and σ1=500

19. Mohr stress diagram will be

20. Cont…
σN = σ1+ σ3/2 + σ1- σ3/2 *cos2Ѳ
σN =500 Pa+(-2000) Pa/2 + 500 Pa- (-2000) Pa/2
*cos(100)
σN = -750 Pa +1250 cos(100)
σN =-967 Pa (Normal stress)
σs= σ1- σ3/2 sin2Ѳ
σs= 500 Pa –(-2000)/2 Pa* sin(100)
σs=1250 *sin(100)
σs= 1231Pa (Shear stress)