Groundwater occurrence in weathered and fractured basalts, Dalha Basalts, Republic of Djibouti


Jalludin, M.; Razack, M.

Memoires - International Association of Hydrogeologists 24: 248-258

1993


248
B12.
M.
JALLUDIN
&
M.
RAZACK
GROUNDWATER
OCCURRENCE
IN
WEATHERED
AND
FRACTURED
BASALTS.
DALHA
BASALTS.
REPUBLIC
OF
DJIBOUTI.
M.
JALLUDIN'
&
M.
RAZACK
'Laboratoire
d'Hydrogeologie,
I.S.E.R.S.T.
B.P.
486,
Djibouti,
Republic
of
Djibouti.
(Tel.
352795;
Fax.354812)
Iaboratoire
d'Hydrogeologie,
Universite
de
Poitiers,
40
Avenue
du
Recteur
Pineau,
86022
POITIERS,
France.
(Tel.
49454017;
Fax.
49453681)
ABSTRACT.
The
Republic
of
Djibouti
(area,
23000
km
2
;
population,
400,000
inhabitants)
has
an
arid
tropical
climate
(daily
average
temperature,
36°C;
annual
average
rainfall,
130
mm)
and
experiences
severe
problems
with
respect
to
providing
drinking
water
for
the
population.
The
only
potential
reservoirs
that
could
provide
sufficient
water
resources
for
current
and
future
needs
are
represented
by
the
volcanic
rocks
covering
the
main
area
of
the
country.
Exploitation
of
the
water
resources
is,
however,
dependent
on
a
good
hydrogeological
knowledge
of
these
reservoirs
(structure,
underground
flow,
type
of
recharge,
etc).
Therefore
intensive
investigations,
including
geophysical,
photogeological
and
hydrodynamical
studies,
were
undertaken
in
order
to
obtain
the
necessary
hydrogeological
data
for
these
aquifers.
The
Dalha
basalts
(3.4
-
9
Ma
old)
fracture
network
was
analyzed
using
aerial
photographs,
SPOT
satellite
images,
and
electrical
geophysics
(Schlumberger
method)
with
the
particular
aim
of
assessing
potential
well
locations.
The
fracture
network
is
characterized
by
a
main
N110°
direction
and
other
secondary
directions,
E-W,
N-S
and
N070°.
Hence,
wells
were
drilled
at
the
intersections
of
these
fractures
at
points
where
the
geophysical
data
indicated
the
greatest
probability
of
groundwater
occurrence
(i.e.
the
layer
of
40
-
70
Ohm.m
resistivity).
The
water
wells
provided
good
quality
water
despite
the
exceptionally
difficult
geological
conditions
of
the
area,
and
showed
medium
permeabilities.
Finally,
on
the
basis
of
the
results
from
this
study,
a
hydrogeological
conceptual
model
was
constructed
to
represent
the
direct
relationship
between
narrow
wadi
underflow
and
the
basalt
aquifer,
which
relationship
controls
the
basalt
aquifer's
recharge.
INTRODUCTION
Water
resources
are
by
far
one
of
the
most
critical
problems
in
the
Republic
of
Djibouti,
where
more
than
90%
of
the
drinking
water
comes
from
different
basaltic
aquifers.
The
Dalha
basalts,
in
the
southern
part
of
the
country,
are
an
intensively
exploited
aquifer
at
the
current
time,
but
until
a
few
years
ago
only
occasional
and
local
studies
of
the
aquifer
had
been
undertaken.
MEMOIRES
OF
TILE
XXIVii.
CONGRESS
OF
MIL
As,
OSLO,
1993
249
The
hydrogeological
research
program,
set
up
in
1991
to
study
fissured
volcanic
rock,
deals
particularly
with
hydrogeological
prospecting
in
the
Dalha
basalts.
This
paper
outlines
the
hydrogeological
features
of
the
narrow
aquifer,
located
between
saline
water
aquifers
unexploitable
for
drinking
water.
GEOLOGY
The
volcanic
series
overlie
the
basement
rocks
(Jurassic
limestones
and
Cretaceous
sedimentary
rocks)
as
a
result
of
the
Red
Sea,
Aden
gulf
and
East
African
rifts
triple
junction
system
(Barberi
et
al.
1975,
Gaulier
and
Huchon
1991),
related
to
plate
tectonic
movements
in
the
last
25
-
30
Ma
(fig.
1).
Old
basalts
or
Adolel
basalts
characterize
the
first
rupture
movement
within
the
Arabo-Nubian
block
which
occurred
during
the
later
Miocene
period.
This
highly
weathered
basalt
is
intensively
affected
by
hydrothermalism.
There
then
followed
a
period
of
slow
expansion
during
which
the
Mabla
rhyolites
outcrop
formed
(15
Ma).
After
an
interval
during
which
these
rhyolites
were
eroded,
the
Dalha
basalts
were
laid
down
with
an
angular
unconformity
(3.4
-
9
Ma).
The
Somali
basalts
outcrop
was
formed
contemporaneously
in
the
eastern
part
of
the
region,
but
remained
in
a
stable
tectonic
area.
L
\.
DORRA
5
12
-
OBOCK
TADJOURAH
ARTA
DJIBOUTI
6
D1KHIL
7
ALI
SABIEM
9
Figure
1.
Geological
map
of
Republic
of
Djibouti.
1:
Jurassic
and
Cretaceous
sedimentary
rocks;
2:
Adolei
basalts;
3:
Mabla
rhyolites;
4:
Dalha
and
Somali
basalts;
5:
Stratokl
basalts;
6:
Stratoi'd
rhyolites;
7:
Gulf
basalts;
8:
recent
basalts;
9:
sedimentary
rocks
250
1312.
M.
JALLUDIN
&
M.
RAZ4CK
Between
3.5
Ma
and
1.5
Ma,
the
Stratoid
basalts
and
Gulf
basalts
poured
out
as
the
Gulf
of
Tadjourah
opened.
The
Gulf
basalts
are
located
on
both
sides
of
the
Gulf
and
are
considered
to
represent
the
first
fissural
lava
flows
of
the
Gulf
of
Tadjourah
ridge.
The
geological
ages
cited
are
those
given
by
Barberi
et
al.
(1975),
Black
et
al.
(1975)
and
Chessex
et
al.
(1975).
HYDROGEOLOGY
AND
RECHARGE
MODEL
The
Dalha
basalt
series
was
first
recognized
by
Marinelli
&
Varet
(1973)
in
the
northern
part
of
the
Republic
of
Djibouti.
In
the
southern
region
they
cover
a
narrow
area
from
the
Gulf
of
Tadjourah
down
to
Ethiopia,
but
the
main
part
lies
in
the
Republic
of
Djibouti.
These
basalts
are
greenish
grey
or
black
in
colour
and
outcrop
in
the
form
of
trapps;
several
metres
thick
lava
flows
with
shrinkage
cracks,
vesicles
and
amygdules,
intercalated
with
ignimbrites,
red
and
green
paleosoils
and
occasional
alluvium
layers.
Intertrappean
layers
are
often
discontinuous
(i.e.
pinching
out).
Within
the
study
area
the
basalts'
thickness
varies
between
250
m
in
the
southern
region
to
400
m
in
the
North.
Red
and
green
shales
with
rare
detritic
quartz
constitute
the
substratum
of
this
geological
formation
(Jalludin
et
al.
1990).
According
to
geological
data
from
wells
and
field
observations,
the
Dalha
basalts
are
characterized
by
two
types
of
permeability.
Horizontal
permeability
occurs
particularly
in
the
interbedded
layers
and
in
the
shrinkage
cracks.
Vertical
permeability
occurs
within
tectonic
faults
which
play
an
essential
role
in
the
aquifer's
permeability
as
they
can
bring
into
communication
several
laterally
limited
horizontal
pervious
or
impervious
layers.
Recurrent
faulting,
hydrothermalism
and
weathering
over
geological
time
all
affect
aquifer
permeability.
The
Dalha
basalts
have
apparently
been
affected
by
each
of
these
factors.
Hydrothermalism
and
weathering,
in
particular,
appear
to
have
decreased
the
overall
permeability
of
the
aquifer.
Where
tectonic
activity
was
low,
the
fault
systems
have
been
rather
intensively
dominated
by
hydrothermalism
and
weathering
so
that
the
faults
have
formed
impervious
barriers
within
the
aquifer.
Hilly
to
mountainous
areas
within
the
Dalha
basalts
outcrop,
characterized
by
high
runoff
and
an
intensively
weathered
surface,
do
not
allow
infiltration.
The
surface
water
drainage
network
is
well
developed
and
conforms
to
the
main
tectonic
trends
within
each
zone,
as
described
in
the
following
paragraphs.
The
main
wadi
beds
are
hundreds
of
meters
wide
and
the
thickness
of
the
sediments
encountered
exceeds
tens
of
meters.
There
is
an
important
underground
flow
related
to
the
wadi
systems
where
wadi
alluvium
is
recharged
during
runoff
generated
by
generally
short
showery
periods.
Wadi
aquifers,
overlying
the
basalts,
then
act
as
intermediates
in
the
Dalha
basalts
aquifer
recharge,
which
occurs
mainly
through
tectonic
faults
and
also
through
horizontal
pervious
layers
(fig.
2).
1
2
19
3
MI
4
7
1
-
X
-
1
5
Ls
I
6
Lid
9
-1
L
-x
-I
8
MEMONES
OF
711E
XX1Vth
CONGRESS
OF
1A11,
AS,
OSLO,
1993
251
4
IP
Figure
2.
Recharge
model.
1:
wadi
alluvium;
2:
Dalha
basalts;
3:
intertrappean
layers;
4:
shrinkage
cracks;
5:
faults;
6:
wadi;
7:
wadi
piezometric
level;
8:
basaltic
aquifer
piezometric
level;
9:
infiltration
from
alluvium
to
basalts
FRACTURING
IN
THE
DALHA
BASALTS
In
the
southern
part
of
the
Gulf
of
Tadjourah,
the
Dalha
basalts
cover
an
area
of
more
than
1800
km
2
.
This
outcrop
displays
an
important
irregular
cluster
of
faults
which
was
subject
to
mapping
during
our
study.
The
area
was
mapped
on
two
different
scales:
1:30,000
and
1:200,000,
using
aerial
photographs
and
spo
-
r
satellite
images
respectively.
The
aim
of
the
mapping
exercise
was
to
characterize
the
surface
fracturing
pattern,
to
compare
it
to
the
different
tectonic
phases
and
to
apply
the
results
to
well
location.
Satellite
images
have
been
used
to
analyse
plate
tectonic
structures
(Bannert
1972,
Kronberg
et
al.
1974,
Girault
1986)
and
SPOT
images
have
been
used
to
study
particular
tectonic
faults
(Tapponier
et
al.
1990).
The
1:30,000
aerial
photograph
and
1:200,000
SPOT
image
surveys
enabled
fracture
maps
for
the
Dalha
basalts
to
be
drawn
up.
The
maps
show
five
different
zones
where
fractures'
extension
and
strike
behave
differently
(fig.
3).
In
order
to
define
the
specific
parameters
for
each
zone,
the
fracture
maps
were
digitized
with
RAFNUM
software
and
analysed
with
RAFORT
software
(Razack
1984).
This
operation
yielded
directional
histograms
for
each
zone
and
the
entire
area.
The
principal
fracturing
directions
in
zone
1
are
NS,
N050°
and
N150°
with
respect
to
the
Arta
transform
zone
(Arthaud
et
al.
1980).
The
fractures
seem
relatively
small
and
dense,
although
the
sparse
EW
fractures
are
long.
Within
the
next
zone
(zone
2),
the
fractures
form
a
more
or
less
regular
network
of
NI60
°
-180°
and
EW
fractures.
Zone
3
fracturing
directions
are
mainly
EW
and
N110
°
-130°,
which
are
superimposed
by
a
network
of
small
dimension
fractures,
in
NS
-
-
*OUEAH
11'3O
5
-0'
luso,
2
DODDOUB
B
AWRAWSA
DAASBIY0
MOUND
-
1*1
a
4
DABADER
-
r -
--
/
- -
o
skm
[42
°
30
GLOBAL
\.
‘\„
142'50
11
Q
00
252
B12.
M.
JALLUDIN
&
M.
RAZACK
Figure
3.
Fracture
network
of
the
Dalha
basalts,
from
SPOT
images
of
scale
1:200,000.
a:
exploitation
sites.
and
N060°-070°
directions.
Zone
4
seems
similar
to
zone
3
with
the
principal
direction
of
fracturing
in
the
range
of
N100°-120°.
This
area
is
characterized
by
faults
exceeding
10
km.
The
N100°
and
N130°
principal
fracturing
directions
of
zones
4
and
3
respectively
are
the
result
of
two
extension
phases.
Around
3.4
Ma
the
extension
orientated
N020°E
was
changed
into
N040°E
after
a
rotation
of
the
tectonic
strain
tensor
by
20°
(Huchon
&
Gaulier
1990).
The
fifth
zone
shows
a
particular
fracturing
behaviour
where
the
fractures
describe
elliptical
curves,
with
a
focal
point
which
could
be
located
in
the
Gulf
of
Tadjourah.
Geomorphological
studies
using
aerial
photographs
(scale
1:30,000)
and
field
observations,
demonstrated
the
tectonic
reactivation
of
the
different
fault
systems
with
a
relative
chronology
(Arthaud
&
Jalludin
1990).
Field
observations
revealed
sealed
fractures
with
secondary
minerals
such
as
zeolite
and
calcite.
.e
-
k
Ls)
v
41
'
24
-
7.7.
0
0
0
0—
56
v
V
V
v
44
ir.,4+
12
49
<1
2
to
<2
3
50
4
1
29
M
139M
MEMO1RES
OF
THE
XXIVth
CONGRESS
OF
1A11,
AS,
OSLO,
1993
253
GEOPHYSICS
Since
1960,
several
geophysical
surveys
were
run
by
Compagnie
Generale
de
Geophysique
(CGG),
Cooperation
Hydrogeologique
Allemande
(CHA),
Compagnie
de
Prospection
Geophysique
Francaise
(CPGF)
and
Institut
Superieur
d'Etudes
et
de
Recherches
Scientifiques
et
Techniques
(ISERST)
over
the
study
area.
The
Sch!umberger
electrical
method
has
been
mainly
applied
to
determine
possible
aquifer
layers
before
commencing
drilling
campaigns.
Analysis
of
results
from
electrical
soundings,
carried
out
adjacent
to
existing
water
wells,
provided
evidence
of
the
variability
of
electrical
resistivities
in
the
aquifer.
Values
ranged
between
10
to
100
rim.
As
an
example,
electrical
soundings
at
water
wells
in
the
DADIN
sector
(fig.
4),
show
electrical
resistivities
of
11
rim
and
50
rim
for
the
volcanic
layers
of
wells
DADIN3
and
DADIN6
respectively.
DAWN:3
DADINb
Figure
4.
Electrical
geophysical
results
for
DADIN
area.
1:
basalts;
2:
scoria;
3:
gravels
and
blocks;
4:
shales
In
the
same
way,
the
other
sites
display
different
electrical
resistivities
for
aquifer
layers:
100
rim
for
well
DABADERE2,
40-60
rim
for
well
DIKHIL2
and
20-50
Om
for
wells
located
in
Mouloud
and
Doudoub
Bolole
area.
Two
factors
cause
these
variations
in
electrical
resistivities
within
the
saturated
zone
of
the
same
volcanic
formations.
The
first
is
related
to
the
intrinsic
characteristics
of
the
rock.
When
the
rock
is
deposited,
the
proportion
of
amygdules
and
vesicles
is
variable.
The
greater
the
proportion
of
these
features
is,
the
higher
the
electrical
resistivity
will
be.
On
the
contrary,
the
greater
the
proportion
of
shrinkage
cracks
formed
and
the
frequency
of
interbedded
layers
is,
the
lower
the
electrical
resistivity
will
be.
On
the
other
hand,
during
geological
time,
volcanic
rocks
acquire
further
characteristics
due
to,
(i)
weathering
and
hydrothermalism,
the
effects
of
which
decrease
the
electrical
resisitivity,
and
(ii)
fracturing,
which
also
decreases
the
electrical
resistivity.
Electrical
resistivity
is
furthermore
related
to
water
salinity
which,
when
higher,
decreases
the
electrical
resistivity
of
the
formation.
MEMO1RES
OF
THE
XXNth
CONGRESS
OF
1A11,
As,
OSLO,
1993
255
Drawdown
data
were
analyzed
with
Cooper
and
Jacob's
method
(1947)
and
recovery
was
interpreted
with
Theis's
method.
Wells
OUEAH8
and
DADIN6
(fig.
6)
draw
water
from
the
superficial
alluvium
aquifer
which
has
a
direct
hydraulic
relationship
with
the
underlying
Dalha
basalts
aquifer.
These
wells
exhibit
typical
drawdown
behaviour
as
described
by
Boulton
(1963),
(i.e.
delayed
yield).
Dr
a
w
do
w
n
(
m
)
DAMN
3
OUFAE4
10
••••
•••••'..
AWRAWSA
3
I°11*4.
DAASBIYO
sa
13
12
11
10
9
6
5
4
3
20
18
16
14
12
30
20
10
0
100
1000
10000
100000
1000000
Time
seconds
Figure
5.
Semilog
plots
of
drawdowns
in
pumping
wells,
Dalha
basalts
aquifer.
6
DAMN
6
4
3
0
••••••••••••aaw•
3
OUEAH
8
10441
1
a
NW
••
0161
NOP
M•
111
U.
brne
-
seconds
0
10
100
1000
10000
100000
Figure
6:
Semilog
plots
of
drawdowns
in
pumping
wells
DADIN
6
and
OUEAH
8.
Transmissivity
values
range
from
3.9
x
10
-5
m
2
/s
to
5.7
x
10
-3
m
2
/s,
indicating
that
the
Dalha
basalts
aquifer
has
poor
to
moderate
transmissivity.
Only
three
surveys
allowed
storage
coefficient
calculation.
According
to
these
coefficients,
ranging
between
256
B12.
M.
JALLUDIN
Sc
M.
RAZ-ACK
4
x
10
-3
and
5
x
10
-6
,
the
aquifer
can
be
categorised
as
a
semiconfined
aquifer.
Some
significant
differences
exist
between
transmissivity
values
deduced
from
drawdown
and
recovery.
The
divergence
of
values
is
related
to
the
Dalha
basalts!
heterogeneity,
due
to
its
particular
geological
stratification
and
to
secondary
effects
such
as
hydrothermalism.
Table
II.
Hydrochemical
data.
Concentrations
in
mg/l.
Wells
Ca"
Mg'
Na'
K+
HCO
3
*
SO.,
-
Cl
-
NO
3
El.con.pH
µS/cm
Dadin
1
45
43
253
1
576
112
162
33
1421
7.7
Dadin
3
59
23
105
5
300
76
93
35
860
7.3
Dadin
6
54
26
232
4
401
129
189
35
1337
7.8
Mouloud4
118
125
377
9
228
373
677
118
2980
7.7
Oueah
8
40
29
171
5
326
84
155
31
1100
7.7
Dikhil
5
78
66
184
3
279
115
317
107
1603
8.0
Dabadere
32
32
188
1
320
130
147
31
1120
8.0
Hindi
62
62
316
5
305
178
502
78
2320
7.8
Goroja
180
132
1172
24
122
552
1985
130
8250
7.7
Ali
Sab.
3
148
127
508
5
364
885
595
2
3700
7.0
Dadahalou
38
63
241
11
249
210
325
20
Hambocto
105
36
257
4
276
156
418
33
PK
50
24
21
165
5
334
75
120
14
1320
8.0
Oueah
6
39
30
178
6
336
81
161
31
1124
7.7
WATER
QUALITY
Hydrochemical
analysis
of
the
Dalha
basalts
aquifer,
the
wadi
groundwater,
(Dadahalou,
Hambocto,
PK50),
the
western
sedimentary
basin
aquifer
(Goroja)
and
the
Jurassic/Cretaceous
aquifer
(Ali
Sabieh
3)
are
compared
in
Table
II.
As
shown
in
this
table,
the
poor
water
quality
of
the
wells
Goroja
and
Ali
Sabieh
3
makes
them
unexploitable.
One
can
note
that
Ali
Sabieh
3
is
located
within
the
eastern
Jurassic/Cretaceous
sedimentary
rocks
and
Goroja
within
the
western
sedimentary
basin,
both
of
which
have
gypsum
intercalations.
Their
high
concentrations
of
chemical
components
are
explained
by
the
negligible
recharge
of
these
areas
and
dissolution
of
minerals
from
evaporites.
The
exploited
wells,
however,
also
show
some
anomalies.
More
than
45
mg/1
of
nitrates
(the
official
international
standard
limit)
were
recorded
in
Mouloud
4,
Dikhil
5
and
Hindi.
Although
some
chemical
components
are
above
the
international
standards
(nitrates,
chlorides,
sodium)
the
local
populations
are
accustomed
to
drinking
these
waters.
At
the
present
time,
the
origin
of
nitrates
in
these
waters
has
not
been
clarified.
Chemical
fertilizers
that
usually
result
in
nitrate-leaching
are
not
being
used
in
this
MEMOIRES
OF
THE
XXIVth
CONGRESS
OF
1A11,
AS,
OSLO,
1993
257
region.
Nitrogen
fixation
by
root
bacteria
is
not
the
cause,
as
vegetation
is
very
sparse.
As
the
nitrate
anomaly
is
noted
all
over
the
country,
except
within
the
Jurassic/
Cretaceous
rocks,
one
hypothesis
is
that
it
could
be
related
to
the
previous
volcanic
activity
of
the
area.
Illustration
of
the
of
hydrochemical
analyses
on
a
Piper
diagram
(fig.
7)
gives
three
different
water
types:
sodium
sulphate
for
the
Jurassic/Cretaceous
formations,
sodium
bicarbonate
and
sodium
chloride
for
the
Dalha
basalts
and
wadi
underflows.
The
sedimentary
Jurassic/Cretaceous
aquifer
constitutes
a
separate
system
from
the
volcanic
aquifer.
The
sodium
bicarbonate
and
sodium
chloride
water
types
are
probably
determined
by
the
recharge
model
of
the
basaltic
aquifer.
The
first
water
type
results
from
recent
infiltration
within
the
alluvium
and,
as
mixing
occurs
with
the
main
basaltic
aquifer,
this
water
type
evolves
to
the
sodium
chloride
water
type.
SO4-C1
Ca•Mg
4
10
6
12
118
2
57
143
1
13
c.)
9
rt
Mg
6
4
it
10
Et
7
2
12
5
13
3
9
141
10
SO4
7
1
213
5
6126
14
11
4
CI
Ca
Figure
7.
Piper
diagram.
CONCLUSION
The
study
determined
the
basic
structural,
underground
hydrodynamic,
hydrochemical
and
geophysical
characteristics
of
the
Dalha
basalts
aquifer,
in
the
southern
part
of
the
Republic
of
Djibouti,
and
revealed
its
capacity.
This
aquifer
is
intensively
exploited
and
the
exploitation
is
increasing
every
year.
As
the
Dalha
basalts
aquifer
is
situated
in
a
critical
position,
surrounded
by
saline
water
aquifers,
the
next
step
will
be
concerned
with
evaluation
of
the
water
resources
and
modelling
of
the
aquifer,
in
order
to
establish
a
management
program.
258
B12
M.
JALLUDIN
&
M.
RAMCK
REFERENCES
Arthaud,
F.,
Choukroune,
P.
&
Robineau,
B.
1980.
Evolution
structurale
de
la
zone
transformante
d'Arta
(Republique
de
Djibouti).
Bulletin
de
la
Societe
Geologique
de
France,
t.XXII,
6,
909-915.
Bannert,
D.
1972.
Plate
drift
in
the
Red
Sea
region
analysed
from
space
photograph.
,
Proceedings
of
the
seventh
international
symposium
on
remote
sensing
of
environment,
Michigan,
17-21
May
1971,
p.
1261-1271.
Barberi,
F.,
Ferrara,
G.,
Santacroce,
R.
&
Varet,
J.
1974.
Structural
evolution
of
the
Afar
triple
junction.
Afar
Depression
of
Ethiopia,
Bad
Bergzabern,
F.R.
Germany,
April
1-6
1974,
Editors
A.
Pilger
and
A.
Rosier,
vol.
1,
p.
38-54.
Black,
R.,
Morton,
W.H.
&
Rex,
D.C.
1974.
Block
tilting
and
volcanism
within
the
Afar
in
the
light
of
recent
K/Ar
age
data.
Afar
Depression
of
Ethiopia,
Bad
Bergzabern,
Germany,
1-6/4/74.
Eds.
A.
Pilger
&
A.
ROsler,
vol.
1,
296-299.
Boulton
N.S.
1963.
Analysis
of
data
from
non
equilibrium
pumping
tests
allowing
for
delayed
yield
from
storage.
Proc.
Inst.
Civ.
Eng.,
26,
469-482
Chessex,
R.,
Delaloye,
M.,
Muller,
M.
and
Weidmann,
M.
1974.
Evolution
of
the
volcanic
region
of
Ali-Sabieh
(TFAI),
in
light
of
K/Ar
age
determination.
Afar
Depression
of
Ethiopia,
Bad
Bergzabern,
F.R.
Germany,
April
1-6
1974,
Editors
A.
Pilger
and
A.
Rosier,
vol.1,
p.
228-231.
Cooper
H.M.Jr.
and
Jacob
C.E.
1946.
A
generalized
Graphical
method
for
evaluating
formation
constants
and
summarizing
well
field
history.
Am.
Geophys.
Union.
trans.
27.
526-534
Gaulier,
J.-M.
1990.
De
1'extension
intracontinentale
a
l'accretion
oceanique:
geodynamique
de
la
Mer
Rouge.
These
de
doctorat,
Universite
Pierre
et
Marie
Curie,
363
p.
Giraud
F.
1986.
Etude
par
teledetection
(Donnees
LANDSAT
MSS)
de
la
region
Lac
Abhe-
Rift
d'Asal
(Repubkique
de
Djibouti).
BRGM.
86DJI
152GEO.
28p.
Huchon
et
Gaulier
J.-M.
1989.
Evolution
tectonique
de
l'Afar
meridional
depuis
3,5
Ma.
C.R.
Acad.
Sci.
Paris.
t.309,
Serie
II.
1215-
1222.
Jalludin,
M.,
Anis,
A.,
Idriss,
G.,
Mohamed,
I.,
San
Juan,
B.,
Gaulier,
J.-M.,
Zotskina,
E.,
Gaffaneh,
A.
&
Haga,
A.
1990.
Alimentation
en
eau
potable
de
la
ville
d'Ali-Sabieh.
Sciences
et
Techniques,
no.5,
p.
13-21.
Kronberg,
P.,
Schonfeld,
M.,
Gunther,
R.
and
Tsombos,
P.
1974.
ERTS1
data
on
the
geology
and
tectonics
of
the
Afar/Ethiopia
and
adjacent
regions.
Afar
Depression
of
Ethiopia,
Bad
Bergzabern,
F.R.
Germany,
1-6
April
1974,
Editors
A.Pilger
and
A.
Rosier,
vol.1,
p.
19-27.
Marinelli
G.
&
Varet
J.
1973.
Geologie,
s
t
ruc
t
ure
et
e
vo
l
ut
i
on
du
sud
du
"
Horst
Danakil".
(TFAI
et
Ethiopie).
C.R.Acad.
Sci.
Paris.
t.276.
Serie
II.
Razack,
,
M.
1984.
Applications
d
e
m
e
t
h
o
d
es
num
e
r
i
ques
et
statistiques
1ident
i
fication
des
reservoirs
fissures
carbonates
en
hydrogeologie.
These
de
doctorat
d'etat,
Univer
s
ite
d
es
sc
i
ences
et
techn
i
ques
du
Languedoc,
384
p.
Tapponier,
P.,
.Armijo,
R.,
Manigh
e
tti,
I
.
&
C
ourt
ill
ot,
V.
1990.
Bookshelf
faulting
and
horizontal
block
rotations
between
overlapping
rifts
in
southern
Afar.
Geophysical
Research
Letters,
17
(1),
1-4.