Alpha Eritrean Engineers Magazine 2015 August Issue

AEEC | October 2011 1

Alpha Eritrean Engineers Magazine AUGUST 2015

VOL 6 NO. 2

A TIMELINE HISTORY OF GEOPHYSICS IN ERITREA

A MESSAGE FROM ONE OF THE EDITORS

LIST OF ENGINEERING OPPORTUNITIES

AEEC e

AEEC | August 2015 1

Engineering

Electrical

Mechanical

Chemical

Civil

CONTENTS AND CONTRIBUTORS

A TIMELINE HISTORY OF GEOPHYSICS IN

ERITREA

HENOK T. TEWELDE

A MESSAGE FROM ONE OF THE EDITORS

FILIPOS ABRAHAM

JOB OPPORTUNITIES

YOSIEF WOLDEMARIAM &

FILIPOS ABRAHAM

EDITORS

SEBLE GEBREMEDHIN, M.S. IN PSYCHOLOGY

DR. ADIAM WOLDEGERGISH, PH.D IN

MOLECULAR BIOLOGY

SAMUEL FESSEHAYE, B.A. IN

ELECTRICAL ENGINEERING

FILIPOS ABRAHAM, M.S, IN

SOFTWARE ENGINEERING AND

YOSIEF WOLDEMARIAM, B.A. IN

ELECTRICAL ENGINEERING


A Message from one of the editors

When I was a little boy my desire to be the best amongst of my peer was strong as is in most of childhood friends. Back then, I did not realized the ingredients of success or what make one successful in whatever life journey he or she takes. As time went by, I came to understand that we all have a magic aspiration to have successful life. It is our unshakeable commitment to achieve our dreams that drives us to get to the stage of success whatever that may be. No matter where we find ourselves, I believe that this commitment is always inside and waiting to be tapped, however, without the commitment many of us struggle to maintain our daily life. So how do we tap commitment? How do we get the sprite out of our own magic desire so success can happen for us?

To succeed in life we need unwavering commitment and passion. These two together make the key ingredients to flourish and be successful! If there is not enough of both present in our life, chances to succeed are substantially reduced.

Passion is extremely good driving force, but “do not let the tail to wag the dog”. Too much passion can make you blind to a number of things around you. As in love, without commitment, too much passion does not create lasting relationships. Being passionate does not cost you that much. It is the strength of your commitment what makes your goal in life attainable, thereby make you a happy person. Dedication is the corner stone when things goes bad or good to get you to your final destination successfully.

Commitment is needed to succeed. Without real commitments, be it good companies or solid family cannot built. Commitment is your interior. It is hard to get in, takes time to learn and it is not that tangible. For an outsider, commitment is hard to differentiate from passion. As I mentioned I am passionate about family relation and I am committed – for me that means that I want to develop myself and my vision about solid family continuously. I am ready to challenge myself to be better tomorrow. Commitment can be expensive. To commit, you have to give up something else – you need to prioritize.

Some people may be happy living life with no commitments and no relationships, but I’m convinced those relationships without commitments are just temporary fixes. I don’t believe that anyone can truly be content with that lifestyle. Maybe you’re happy now, but each relationship will be less and less satisfying until you eventually realize how soulless and disassociated from humanity you’ve become. If you’re anything like most people I’ve met, you’re very competitive. Competition is natural for us because we’re sophisticated animals and it is part of our nature to be in competition with each other. We will always be on this life-long pursuit of “something better,” whether it’s by traveling, a new career path, a new significant other, or even a change in lifestyle.

You don’t always need to drop one thing in exchange for the other; you can travel with a significant other or you can change your lifestyle by pursuing a new career. Ultimately, commitments don’t have to be treated like trading cards. You may think there’s someone out there who’s better than what you have but the same goes for them. That person chose you so don’t be an ass and drop them when you think you can “upgrade.” Everyone I know, including me, has self-prescribed anxiety and we all believe that there are deep-rooted issues that cause us to have commitment issues or which create the anxiety that causes us to end things before they begin. We all have experiences and the past is a significant factor in how we conduct ourselves in the present or future. Experiences work like shock therapy; you get burned enough times and you naturally become conditioned to stop doing it.

Don’t put off committing to anything including someone tolling you to wait. Regret is something a lot of people experience every day and time is something you can’t ever get back, so why waste it because you told yourself that you had time? Time doesn’t wait for you, so don’t wait for it.

Sincerely yours,

Filipos Abraham

IN LIFE THE MOST

IMPORTANT WEAPON IS

COMMITMENT TO YOUR

FAMILY, WORK AND

GENERALLY YOUR LIFE.

“To live and die

without knowing

what you could be is

worse than death

itself, therefore

throw yourself at

your dream with all

your strength and

commit to it and

only then that you

will see you are fully

living” TD Jakes

together is a

beginning.

Keeping together is

progress.

Working together is

success.

~ Henry Ford~


My name is Henok Tewelde and I was born and raised in

Asmara, Eritrea. Growing up I had a passion for science

and technology. While in Eritrea,

due to my limited resources I found

myself having to acquire much of

my knowledge from books and the

multimedia.

After graduating with a Bachelor’s of

Science degree in physics and

geology at University of Asmara in 1998 I began working

at the Water Resource Department. Working within the

department broadened my knowledge of the geosciences

particularly with the emphasis of practical application in a

field environment and I eventually became the

department’s geophysics leader. Our department’s main

focus was on exploration geophysics which gave me a

broad base of experience in this discipline. While Eritrea

does not have a Master’s program in Geophysics I

continued my quest for higher learning and level of

education by taking online courses until I had achieved

where I wanted to be. During this time my thoughts were

on the future geophysicist in my country and the hurdles

they would have to cross. Thus, I decided to write a book in

exploration geophysics based on the Eritrean geological

context to help future generations in the study of

geophysics.

The term of geophysics was probably first used in

Germany, where it appeared in scientific writings of the

mid-19th century. The word geophysics was first used by

Fröbel as "geophysik" in 1834. Gilbert’s discovery that the

earth behaves as a great and rather irregular magnet and

Newton’s theory of gravitation may be said to constitute

the beginning of geophysics. Mining and the search for

metals date from the earliest time, but the scientific record

began with publication in 1556 of the famous treatise

De re metallica by Georgius Agricola, which for many years

was the authoritative work in mining. The initial step in

applying geophysics to the search for minerals probably

was taken in 1843, when Von Wrede pointed out that the

magnetic thedolite, used by Lamont to measure variations

in the earth’s magnetic field, might also be employed to

discover bodies of magnetic ore. However, this idea was

not acted on until the publication in 1879 in Professor

Robert Thalen’s book on the Examination of Iron Ore

Deposits by Magnetic Methods. The Thalen-Tiberg is a

magnetometer manufactured in Sweden, and later the

Thomson-Thalen instrument, furnished the means of

locating the strike, dip and depth below surface of

magnetic dikes (Telford, Geldart and Sheriff Applied

Geophysics 1990).

As the name implies, geophysics is a branch of earth

science that studies the physics of the earth, planets and its

atmosphere. It is divided into two major scientific broad

fields: Solid Earth Geophysics and Exploration Geophysics.

Each field is further branched into many arrays of sub-

disciplines. Solid earth geophysics (also known as global

geophysics) comes up with global variables depending on

physical and chemical properties of the earth including

Seismology ,Volocanology ,Geodesy , Tectonophysics ,

Geomagnetics , Geothermy , Geoelectric , Gravimetry etc.,

whereas exploration geophysics (also known as applied

geophysics) yields local variables based on the physics and

chemistry of the earth. Some of the examples are Hydro-

geophysics, Hydrocarbon geophysics, Geothermal

geophysics, Mining geophysics, Engineering geophysics,

Archeological geophysics, Environmental geophysics.

Geophysics plays a pivotal role in using subsurface

treasures wisely and equitably, it greatly sub-serves as a

source of complementary science to all earth sciences as

Well as to the field of Construction Engineering in the

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A Timeline History of Geophysics in Eritrea


safety of building infrastructures.

Therefore, one can speculate that a discipline such as

Geophysics could help in maximizing economic growth and

development in an environmentally friendly manner. It

introduces ecological balancing factors into the equation of

feasibility studies for the advancement of all human kind.

Therefore, in order for the Water Resources Department-

Geophysics Unit (WRD-GU) to be an efficient subsidiary to

other sectors of the country, these main goals have to be

met. Encouraging high professional standing, scientific

excellence, and skills required to expand into new

disciplines and services.

The main factors to enhance geophysical activities are to

upgrade the level of accuracy (to progress with rapid

change in technology) and the level of precision (to

increase the ability of personnel involved in the field of

geophysics) in the geophysical carriers.

The geophysical instruments available in WRD are based on principles of physics to predict the possible geological layers and fluid dynamics of the earth constituents. These principles are described below chronologically in their respective geophysical methods:

1. Electrical methods

A primitive instrument was used relative to the cutting edge now due to increasing in Artificial Intelligence (AI) and machine learning. These in turn increase the actual processing and restoring of their memory for the main CPU of the geophysical instrument. Therefore, the old traditional instrument was DCRES200 Terrameter manufactured by South African Red Dog Scientific Services. Spontaneous potential is manually compensated (Where as nowadays auto-compensators are used for the natural voltage). This instrument has two different units that measure the potential and the current injected down into the earth, then the geophysicist himself calculates the earth resistance. This instrument was introduced in the WRD-GU at the end of 1995 (5ii88). See figure1 below.

Current meter

Volt meter

Figure1. Terrameter DCRES200

In electrical method, the geophysicists’ worked with this type of instruments until 1999. In 1999, an upgraded version was purchased from ABEM Sweden. This instrument was called SAS 300B (Signal Averaging System 300B). In 2000, it was again upgraded into SAS 300C. This instrument had auto-compensator therefore there was no need to make nullification by the geophysicists. Moreover, the instrument itself calculates the earth resistance.

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However if the Terrarmeter becomes agitated by highly resistive geological materials like “loose sand” for example a booster has to be connected with the main instrument to alleviate the dissipative work done by the flow of charges or current from its transmitter to energize and harness the output of the current density due to the electric field or equi-potential surfaces. Then finally, to be interpreted into possible geological outcomes based on the electrical properties of the earth at different data levels. The SAS 300C is shown below in figure2:

Figure2. Terrameter SAS 300C

In 2004, the geophysics unit in WRD introduced Campus

Ohmega a Terrameter made in England. This is an

authentic instrument which has a versatile CPU embedded

in the instrument. If the electrode selector is purchased a

2D and 3D resistivity and IP (Induced Polarization Method

part of the electrochemical activity) can be measured at the

same time along with lapse resistivity and IP. Therefore, it

is so easy to depict the spatial and temporal variation of the

electrical properties of the earth. The instrument is shown

below in figure3:

Figure3. Terrameter CampusOhmega

In 2006 Professor Antonio Galgaro, a friend, leading

scientist in predicting the submerging vertical velocity of

the Venezia island and president of the geophysical

institution in Padua University Italy donated the WRD-GU

a TessaII type of instrument which he designed and named

after his wife. It is shown below in figure4:

Figure4. Terrameter TessaII

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At the end of 2006 a brand new SAS 1000 ABEM

terrameter, which serves 2D and 3D resistivity, IP (induced

polarization) and SP (spontaneous potential) was

Thank you for sharing with me the June issue of Alpha Eritrean Engineer’s

Magazine.

I believe it is a good start to a well needed magazine. I enjoyed the inspiring

article as well your attempt to connect those who need jobs to the job opening

opportunities.

Engineer Daniel

Brain experience on Days in a month question answer: Question: Some months have thirty (30) days and some months have thirty-one (31) days. How many months have twenty-eight (28) days? Answer: The answer is all 12 months have 28 days. It is true only February has 28 days however, the rest of the months have either 30 or 31 days which means they already have 28 days and more.

Comments & Suggestions

Page

ALPHA ERITREAN ENGINEERS

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purchased. This instrument is with a variety of

symmetrical and asymmetrical electrical geometrical

arrays of electrode configuration. The various geometrical

earth constants may be used for different purposes such as

in depicting speedy economic particle flows, viscous

economic particle flow, static economic grains and all

safety variables in engineering and environment. A

separate electrode selector that can be connected to the

terrameter is called ES464 as shown in figure5.

Figure5. Terrameter SAS 1000 with its corresponding ES

464

In 2012, a highly portable brand new Terrameter LS was

purchased from ABEM. This instrument is all in both the

Terrameter and electrode selector which are in one

console. Moreover, if wide area network is available the

field geophysicist can directly send the raw data from the

field to the office geophysicist in the city. At the same time,

it has many other different features. In short, it is a highly

sophisticated gadget that measures the electrical behavior

of the earth.

The higher order accuracy is needed due to various

mineralogical compositions of the geological features of

rocks, soils, clay content and fluid content of the subsurface

of the earth affects resistivity, IP and SP. The Terrameter

LS (see figure6) can show preliminary results on the

instrument’s monitor and has all the Microsoft offices, pdf

(portable document format).

Figure6. Terrameter LS

2. Electromagnetic methods

In 1997 WRD geophysics unit purchased ABEM WADI instrument in order to serve for shallow investigation purposes. This type of instrument measures total Very Low Frequency (VLF) with real and the imaginary components of the wave for an electromagnetic band. This type of EM method is passive geophysical survey because it has only a receiver and the transmission of the electromagnetic band galvanic sheet current that come to the target area is disseminated by the developed countries for their own different purposes.

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Figure7. ABEM WADI, VLF instrument

In 1998, the WRD-GU purchased EM-34-3 type of

instrument from GEONICS to measure the distribution of

conductivity of subsurface soils and rocks using FDEM

(Frequency Domain electromagnetic Method).

This serves for shallow investigation purposes. In 2012, an

updated version EM-34-3 was purchased. This newer

version had a GPS embedded in the instrument that tell us

the geographical coordinates of the location for the data

acquisition point with respect to prime meridian, equator

and altitude of the earth.

Figure8. EM-34 FDEM instrument

In 1998, the WRD-GU purchased Time Domain

Electromagnetic Method (TDEM) protom type TEM-57 and

TEM-67 instruments from GEONICS. This instrument is

ideal in distinguishing seawater to fresh water interface. At

the same time, it is good for deep targets of investigations.

In 2012, a new version with GPS capability and advanced

sophisticated features was purchased from Terratem

Australian geophysical industry.

Figure 9. TDEM instrument

In 2012, the WRD-GU purchased an instrument

Magnetotelluric/Audio Magnetotelluric (MT/AMT)

instrument from PHONIX a Canadian geophysical industry.

This instrument has the capability to measures from the

shallowest to the deepest part of the earth’s crust with all

the geographical coordinates and synchronized clock

relative to the place of investigation. Depth varies as a

function of frequency. It is a passive method where the

source is uncontrolled due to the ionosphere affects the

subsurface induce telluric currents. This instrument is also

helpful for solid earth geophysicists because its depth of

penetration can reach down to the mantle. See figure10.

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Figure 10. MT/AMT instrument

3. Magnetic methods

In 1997 GSM-19 type of Magnetometer from GEM Canadian company arrived to Asmara WRD geophysics unit see figure11. This instrument measures total magnetic field of the earth. The magnetic anomaly is created by the magnetic field of the earth and the causative geological body.

This is due to high magnetic polarization of ferromagnesian minerals. An updated version of this instrument was provided to WRD-GU in 2012.

Figure 11. GSM-19 Overhauser Magnetometer

In 2006, a magnetometer, which can measure a VLF at the

same time, came from a Canadian Company Scintrix. This

Envimag type of instrument measures both magnetic

method and electromagnetic method at the same time. It

needs tie point, loop point or base station correction for the

data. Transmitted EM energy of the VLF field from

developed countries may cause the magnetic method to be

affected by a diurnal variation upon the raw data. The

instrument is shown in figure12 below:

ALPHA ERITREAN ENGINEERS MAGAZINE

AUGUST 2015 ISSUE

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Figure12. Envimag type of VLF embedded magnetometer

4. Seismic methods

In 1997, a seismograph from GEOMETRICS, a San Jose, California company, delivered to Asmara WRD-GU. This geophysics equipment is ideal for engineering geophysics purpose. Hence, the instrument enabled to measure seismic reflection and refraction surveys based on the subsurface density and elasticity of rocks and soils. In 2005, from GEOMETRICS highly sophisticated instruments such as Strataviso and Geode types of seismographs were purchased.

Figure13. Smartseis and Geode GEOMETRICS

seismographs.

Actually, the same seismograph was brought from ABEM

which was the same as Geode. The data acquisition

software is externally commanding it. This is done by

connecting a laptop using RAS24 seistronix software.

Figure14. RAS24 Seismograph

In 2012, highly sophisticated and updated type of

seismograph was purchased from ABEM as shown in the

figure below:

Figure 15. Terraloc-pro Seismograph

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5. Gravity methods

In this type of geophysical method, the gravity meter measures the variation of earth’s gravitation variation. This is due to density of rocks, soils and fluids of the earth, shape of the earth, geomorphological variation and depth of the causative body. In 2006 a Sodin type of gravimeter was purchased from a Canadian company. See figure16 below:

Figure 16. Sodin type of gravimeter

6. Radiometric methods

Radiometric surveys are less widely used than the other geophysical methods as they seek a very specific target. Probably the most common application of radiometric techniques is in geophysical borehole logging. Radiometric surveying is employed in the search for deposits necessary for this application, and also for non-radioactive deposits associated with radioactive elements such as titanium and zirconium. Radiometric surveys are used in geological mapping as different rock types can be recognized from their distinctive radioactive signatures. At least 20 naturally occurring elements are now known to be radioactive, but only uranium (U), thorium (Th), and an isotope of potassium (K) are important in exploration geophysics because most radioactive signature rock forming minerals have the three isotopes. In 2006, the WRD geophysics unit bought from MOUNT SOPRIS Denver, United States.

Figure 17. Radiometric instrument.

Deploying all the instruments above, we used and were

able to cultivate geophysical raw data by the methods

mentioned. However, the data are ambiguous due to noises

that are embedded with the raw data. Henceforth, in order

to rectify its knowledge mathematical algorithms and

mathematical filters are highly essential. There are two

types of noises; these are the random noise and the

coherent noise. The random noise is the cultural noises like

buried metal, high power electric transmission, buried

plastics, ditches etc… that may detract the path of induced

currents which distort the shape of the equipotential

surfaces. The coherent noise is embedded in our main raw

data for example the surface waves in seismic methods

(Rayleigh wave, love wave, stonely etc.) superimposed to

the P and S waves. Sometimes due to high anisotropic ratio

(lateral and radial variations of the geophysical

parameters ratio), an equivalence problem (different

models in the interpretation software can fit the same

geological configuration) can occur. Therefore, to increase

the signal to noise ratio we need signal/data processing.

That’s why, data processing in geophysics needs advanced

mathematical techniques to avoid the unnecessary noises

blended with our main data. Then further interpretation

techniques are needed after processing either using or

based on the concept of both geology and physics.

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Listed below are a few samples of geophysical

interpretations using the variety of geophysical techniques

in Eritrea:

Eritrea purely magnificent

A land of Glorious mountain road where ordinary people are

born, train, paddle and elevated to kingship on the world

stage.

The creativity, ingenuity and originality of Civil engineering at its best!


a. Groundwater geophysical study in Alla valley using

Electrical and electromagnetic method in the year

2004.The following figures shows the

interpretation of high to low conductivity anomaly

using electromagnetic method varying the

frequency to increase depth by using the 20 and 40

both horizontal and vertical dipoles.

Figure18. Superposition of 1D - FDEM electromagnetic method

Based on the electromagnetic anomaly further electrical

methods have been carried out to depict the shape of the Alla

valley bedrock profile. It helps to calculate aquifer thickness

that serves to set hydrogeological parameters. Mathematical

groundwater flow modeling has been set to calculate the

hydraulic conductivity and transmissivity coefficients of the

aquifer. The geophysical study played a great role in

predicting the thickness of the overburden and the weathered

granite, terrain slope of the massive bedrock and local

groundwater flow pattern as shown in the figure19 below.

Engineer Kibrom and Henok during Alpha event

Figure19. Bedrock profile of Alla valley using

electrical methods

b. Example of environmental geophysics using TDEM

and Resistivity:

In this example, the environmental geophysical

study has the biggest role in defining the seawater

intrusion in order to save the Beilul coastal village

from evacuating in the next five decades. This

study was completed in 2003.

Figure20. TDEM of Survey in Beilul aquifer

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c. Example of Engineering geophysical surveys:

This depict the massive and competent shallow

bedrock in order to attain the magnitude of bearing

and loading capacity. To assure the existence and

orientation of geological structures that may

hamper construction of a dam around Afhimbol

area a geostatistcal analysis was conducted that

enabled us to calculate the increment of slope

height that may lead to fatigue and..settlement.

Figure 21. 3D-magnetic survey in Afhimbol in

2009

Engineering geophysical study around Gedem cement

factory enabled us to identify the foundation and bearing

capacity of the soil during construction of the factory.

Figure22. Contour map of seismic refraction around

Gedem in the year 2007

561517 561573 561629

Easting (UTM)

GEDEM TOP SOIL PROFILE

1714850

1714900

1714950

1715000

1715050

1715100

1715150

1715200

1715250

1715300

1715350

North

ing (U

TM)

00.511.522.533.544.555.566.577.588.599.51010.51111.51212.513

DEPTH (m)

Average velocity in this layer is about 348 m/s.

BE A PART OF

IT IT CONNECTS

IT INFORMS

IT SHARES EXPERIENCES

AEEC

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d. To study the impact of hydrostatic pressure in the

mining engineering design of the Bisha mining in

the year 2010.

Figure23. Integrated geophysical study over the

Bisha mining envelope

Looking at the above samples interpreted geophysical

information the reader can understand that competence of

a geophysicist principally depends on the following traits:

Knowledge of his/her subject matter. Mastery of Physics, Geology and Mathematics. Flexible in using the principles of geostatistics to

attain the processed data, which reflects the real situation of the field.

Expert knowledge in setting field set up parameters, processing parameters and interpretation measures.

Essential skills of computer techniques.

That is why highly skilled geophysicists are needed to increase the level of precision that the probability of interpretation becomes close to reality. Therefore, human resources assignments in the WRD are sought and needed with major either in physics and minor geology or vice versa.

How do earthquakes happen? Moreover looking at the

solid earth geophysics versus East African rift system and

quake a preliminary qualified guess can be drawn. Above

98% the factors that cause earthquakes are internal in

origin. Even if, we have gravitational forces from moon,

other planets and celestial bodies are continually

deforming the earth. It is insignificant from the perspective

of an earthquake. The earth scientists and especially the

seismologists are immensely experienced on experiments,

theories (for example drift of continents), earth

philosophies, Wisconsin cycle and so on. They strongly

believe in the upper core part of the earth where high

density liquid exists. Hence, due to the convective and

adventive magmatic cells of the high density liquid that

drives a certain force to the upper mantle, which in turn

energy is generated in the astenosphere. This has plasticity

characteristics and compensation is under taken with

roots of the crust and anti-roots of the mantle into the crust

and especially into oceanic crust. So, nature is counter

balancing itself all the time to keep its own equilibrium.

You might have heard about the plate tectonics that lead us

to subduction processes, sea floor spreading and creation

of the oceanic ridges. The plate tectonics is mainly due to

the oscillation of the astenosphere that causes it to break

up the lithosphere. According to UPSeis who are an

educational site for budding seismologists, earthquakes

are usually caused when rock underground suddenly

breaks along a fault. This sudden release of energy causes

the seismic waves that make the ground shake. When two

slabs of rock or two plates are rubbing against each other,

they stick a little. They do not just slide smoothly; the rocks

catch on each other. The rocks are still pushing against

each other, but not moving. After a while, the rocks break

because of all the pressure that has built up. When the

rocks break, the earthquake occurs. During the earthquake

and afterward, the plates or blocks of rock start moving,

and they continue to move until they are stuck again. The

spot underground where the rock breaks is called

the focus of the earthquake. The place right above the

focus (on top of the ground) is called the epicenter of the

earthquake. On September 18, 2013 an earthquake struck

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AEEC

……. Sense of humor from engineer’s prospective

Engineer’s wish and A Genie

A hardware engineer, software engineer and program manager had a morning

customer meeting. After leaving the customer's office, they come across an old brass

lantern in the parking lot. One of them picks up the lantern and rubs it. A genie

appears. Seeing the three men, he offers each one wish.

The software engineer answers first. "I want a yacht in the Caribbean with an all-

women crew." Poof, the software engineer disappears.

Next, the hardware engineer speaks up. "I want an all-women motorcycle gang,

cruising the southwest." Poof, he disappears.

Finally, the genie then turns to the program manager and asks, "What would you like?"

The program manager looks at his watch and replies, "I want them both back by 2 pm

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Eritrea with a magnitude measured 5.0 on the Richter scale

at a depth of 9.8Km. On the basis of the above conceptual

logic from UPSeis I presume perhaps the fault corridor

around Redsea coastline might have differential slipping

that could cause the earthquake. To see how these stresses

are changed into waves like the P-waves (longitudinal

waves that is only due to dilatational or compressional

tensions). Whereas the S-waves (transversal waves) less in

velocity magnitude than P-waves are due to tangential

forces / shear forces and they never pass through liquids.

That’s why P-waves are the first arrivals in our

seismograph. Let me make very generic mathematical

aspects of it:

𝜌𝜕2∆

𝜕𝑡2∝ ∇2∆

Where 𝜟 = dilation, K= bulk modulus and µ= rigidity

modulus

From classical mechanics; Newton’s 2nd law of motion the

product of density and acceleration is pretty much known

that it is unbalanced force per volume. So this force per

volume of the rock masses is directly related to the second

order derivative of the tensile stresses or dilations over the

happening area. Therefore, from mathematics we know

that in order proportional to be equal it needs to have

proportionality of constant but in our case it has physical

meaning we call it the axial modulus which is the sum of

bulk modulus and four third of rigidity modulus.

2

2

t

= 23/4 k

Let

3/42

kVP

………………..

So VP is the velocity of the P-waves.

2

2

2

1

tVP

= 2

We know from physics this is a wave equation. This is how

the wave is forming in the crust of the earth but with its

simplest version of it. Finally, we shall try to know the

difference between risk management and disaster

management.

Risk. Management Scientific and technical studies

Disaster. Management Emergency response studies

Risk management group need scientifically capable

experts that can draft master plans for earthquakes, floods,

and landslides with hi-tech state of the art equipment and

tools that help their entire study. Personnel in the risk

management field have to be experts in proactive

measures. Whereas disaster management personnel are

acting in reactive measures, meaning that they study on

how to mitigate disasters.

On July 3, 2013, I was in Kampala during this earthquake

at an internet café, when a moderate magnitude

earthquake happened about 70Km epicenter distance

from Kampala, measured 5.7 on the Richter scale and at a

9.8Km depth in Lake Albert. Lake Albert is located in the

boundary of Uganda, Democratic Republic of Congo and

South Sudan. The tables began to shake; the computers

were rocking back and forth and at that moment I knew an

earthquake had hit. After the earthquake, some scientists

predicted insignificantly that the cause could have a root

network on the tectenophysics impact of the eastern triple

junction due to trans-tension effect. The triple junction is

the tension pull between three tectonic plates. These are

the Nubian plate (Somalia plate), Arabian plate and Indian

Ocean plate. In my reading on the internet, a few different

observations and predictions were told. However, the

strong debaters were saying, it is due to dynamic effects of

geological structures around Lake Albert itself. Having

studied the rift through Eritrea, as part of this triple

junction there could be a reason to believe some seismic

activity started along this rift area. To quantify each

parameters and dynamic variables using some numerical

techniques is concerned to the one involving there taking

the historical seismic data all the time. I would say what are

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the correlation factors or coefficients that might help to

associate certain predictions with the recent earth quake

happening in Eritrea in September 18, 2013 with an

epicenter distance around 67Km from the capital Asmara

at a depth of 9.8Km which is moderate in magnitude. I

would look forward to a geological survey with a

synergistic approach in East Africa. In addition, have the

results posted with the East Africa Geological Organization

(If such an organization exists). The distance between Lake

Albert and Massawa is approximately 2000 Km and the

direction from Massawa is SSW as shown in the figure

below.

Figure 24. The epicenter spots of Uganda and Eritrea

http://www.nationsonline.org/oneworld/map/google_map_africa Seismologists continuously interpret and analyze their data. Then they superimpose it and try to develop correlation functions by calculating co-variance of the happening. Then from probability theory, it is known that the probability is conserved in terms of 4D. Taking the product of co-variant and contra-variant tensors, the current of probability density function remains constant.

So applying the Gaussian or any other compatible mathematical algorithms, they try to predict the probability of occurrences. Then it helps to prognosticate the risk as a function of time though the probabilistic outputs rely in a range of time. Eritrea needs an early warning system that coincides with other systems throughout the North East African region.

Geologic factors are affecting planning and designs of most infrastructures on this blue planet. The assessment of groundwater, mining, geothermal, hydrocarbon, and the delineation of subsurface pollutions, require sufficient knowledge of geological features and the processes involved in their genesis and evolution. Exploration geophysics, one of the oldest earth sciences, is an essential tool for acquiring knowledge for such assessments. This tool is applicable particularly in the study of applied geology, which focuses on the effects of geological phenomena on human life and how humans can trigger geological processes. In Eritrea, a country in the horn of Africa by the Red Sea, there have been extensive progresses made in the science of geophysical exploration in the past few decades as you have seen in the above. These experiences in exploration geophysics in Eritrea have been documented as a finished manuscript for publication in the near future. The proposed book includes the science of exploration geophysics with due emphasis given to hydro-geophysics based on my experiences in this area. Moreover, problems are designed and included in the book based on the Eritrean geological context.

A sample of the problems addressed in the book:

Problems of Seismic method

a) In February, 2007 a ground geophysical study was carried out in Sawa western Eritrea in the flat plain. The objective of the study was to identify qualitatively the geometry and age of lacustrine sediments (Mesozoic and Cenozoic) following their depositional historical pattern. It is possible to have some geological features in the deposit area. The main concern of the professionals was sustainability by predicting hydraulic conductivity, transmissivity and the boundary of old to young groundwater saturation of

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http://www.nationsonline.org/oneworld/map/google_map_africa

http://www.nationsonline.org/oneworld/map/google_map_africa


the Sawa aquifer. The study of Eritrean hydrogeologists presumed that the Sawa aquifer is recharged both vertically by the rainfall and horizontal flows from the ephemeral Sawa River and other tributaries. Therefore, the Sawa groundwater flow paths are assumed to be a bi-modal flow regime (both piston and diffuse flow models). Figure25 shows a portion of a processed and interpreted 2D-seismic refraction velocity model of the study area. Considering the physics of the fluvial processes from sedimentology we can learn fractional volume of granular pore index is the void ratio (volume of gases plus water to volume of solids), water volume ratio is the volume of the water to the volume of solids and saturation is the volume of the water to the volume of the fluids. Based on the above parameters for geological genesis and evolution assume the Sawa aquifer comprises soil moisture zone and saturation zone. Suggest your delineation on the seismic anomaly and associate the geophysical signature with the aquifer dimension as a function of depth. If the author interpreted the base of the LVL (low velocity layer) of the seismic stratigraphy to be at the groundwater table spatial variation (∂h/ ∂z) under steady state condition assuming coefficient of seismic absorption and Poisson’s ratio perhaps bigger in the low velocity zone. How would you assimilate the LVL in the 2D-Seismic refraction section based on this limited geophysical information.

Figure25. 2D-Seismic section of Sawa aquifer

b) The following time versus distance graph is for the forward profile from a portion of the survey in Question1. Two subsurface velocities are noted in the graph based on the observation of the two

c) linear slopes (5 ms/10 m and 8 ms/20 m in the first and second segments respectively).

Figure26. Time versus distance graph of raw data of

Seismic of Sawa investigation area

If the time intercept is 5.9 ms and the critical distance is 59m determine the thickness of the first geological layer. Show your work using both the time intercept and critical distance and attempt to use all formulae in your answer.

d) Given a coefficient of seismic absorption of fine-grained Greywacke rock is 0.16 db. per wavelength, assume the frequency is 1Hz with wave speed of 2Km/s in the medium. If the distance between the points where the Greywacke attenuating the amplitude of the seismic wave and surface of the wave incidence is assumed to be 1170m, by what percentages will the seismic wave energy be attenuated while traversing through the unit up to that point? Round your result to two decimal places as needed.

Hint: ln10=2.3.

4

Slope=1/V1

Slope=1/V2

10 9

8

7 6

5

3

2

Mill

isec

on

d

1

20

30

40

50

60

10 20 30 40 50 60 70 80 90

Meter

1

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Given an isotropic sedimentary unit similar to the one in

Question 2 with two distinct horizontal beds, prove the

following relationship is true:

tan2 (sin−1V1

V2) =

V12

V22 − V1

2

Hint: apply Snell’s law for seismic refraction method, trigonometry and the geometry of ray paths in time intercept method in the proof.

I. Explain why the left and right hand sides of the

equation become large when the velocity

contrast between layer 1 and 2 tends to zero.

What happens when the velocity contrast

becomes very large? In each case, what is

happening to the seismic wave that is impinging

upon the interface of layer 1 and 2?

II. Based on your conclusions in part (a) of this question, suggest whether the response to the seismic signal of an acoustic impedance (the product of density and velocity) variation of the P-wave is due to hard rocks or soft rocks. Explain why?

The primary purpose of this book is to provide the reader with working knowledge of the art and science of exploration geophysics and to further help the reader adopt this book as a reference for convenience. The book comprises of theories, derivations and deductions of formulae and their relationship with the physical insights.

The conceptual utilization of each tool such as electrical, electromagnetic, magnetic, seismic, gravity and radiometric methods, as reliable and valid model of acquiring information pertinent for this study, has been discussed in detail. To provide the reader with practical impressions, case studies such as the application of geophysics in engineering, hydrogeology, and environmental sciences are addressed. Furthermore, the book provides the reader with the benefits of some additional insights by asserting the results of the author’s fieldwork for proving the practical application of the science.

Eventually, recommendations and practical troubleshooting solutions for problems that arose in the author’s real life situations during exploration are documented. In the long run, the author contends that the book is also expected to be a great asset in developing analytical thinking and stimulating teamwork skills for geophysicists. Although in its early stage, the contribution of the book in upgrading professional standards, best practices in science and ethics is profound.

My sincere appreciation is given in advance for any critics, comment, complement, questions, ideas and information from all interested readers.

By Henok T. Tewelde Senior Geophysicist Head of Geophysics unit for WRD, Eritrea (10/2007 – 06/2013) North Carolina, USA

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e ALPHA

ERITREAN ENGINEERS MEGAZINE

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Bringing the best and the brightest together

Hard to reach doesn’t have to mean hard to do

The authors

Henok Tewelde

[email protected] received his BS degree in physics and geology at University

of Asmara in 1998. Currently Henok is

working hard and fundraising to publish a

scientific book. He can be reached via his email

liseted above.

Filipos Abraham [email protected]

holds Master’s Degree in Software Engineering

from Wichita State University. Currently he is

working with Boeing Defence Space and

Security as designer and embedded real time

software developer.

If you need an updated information,

discussions or got an Engineering

experiences that you want share

your knowledge or ideas with your

fellow professionals.

You will find us on

www.linkedin.com/groups/Alpha-

Eritrean-Engineers-Community

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mailto:[email protected]

mailto:%20%[email protected]

Documents

Alpha Eritrean Engineers Magazine 2015 August Issue