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GEOPHYSICAL FIELD SCHOOL Lake Balaton, Hungary August 31 to September 14, 2007. Multielectrode Resistivity survey. ( MUEL1 ). MOHAMED AL RAJHI, MARTIN VEASEY, EVA PUDLEINER, PETER TAKA’CS. Satellite image of the Carpathian Basin. By NOAA17. Introduction:. - PowerPoint PPT Presentation
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GEOPHYSICAL FIELD SCHOOLLake Balaton, Hungary
August 31 to September 14, 2007
MOHAMED AL RAJHI, MARTIN VEASEY, EVA PUDLEINER, PETER TAKA’CS
By NOAA17
Our survey was part of a geophysical project in the Pannonian-basin .
Different methods were used to better our understanding of the evolutional chapters of Lake Balaton.
The large scale structure is the extensional basin (due to subduction of African Plate), which suffered later from compression.
Enying Ridge
Lake Balaton
N
15km
•The Enying ridge (South from Lake Balaton’s Eastern shore ) is a significant geological structure in the region but the reason
for its existence is unclear.
•The resistivity survey attempts to address this problem and give some possible interpretations.
K is a geometric factor that depends on the arrangement of the four electrodes
*Current (I) is directed into the ground via two outer electrodes (C1 & C2).
*The potential difference (∆Φ) is measured at various points (P1 & P2)
between the current electrodes .
*Apparent resistivity (ρa) is given by:
ρa= k (∆Φ/ I)
*Porosity
*Degree of water saturation in the rock
*Pore space connection
*Dry or wet conditions
ARES-G4
*ARES-G4 control box measures current, voltage & apparent resistivity.
*5 cables are used in the array .
*Cable length is 32m .
*Electrode Spacing is 4m .
*Spread length is 156m.
*Maximum Depth ≈ 30m.
Electrode-Cable Connection
M.H.Loke, 2004
*The Schlumberger array works by keeping the potential electrodes at constant seperation while the current electrodes are expanded.
*The Wenner array works by keeping constant spacing between
all the electrodes .
* Wenner-Schlumberger is a combination of the two.
*Topography from GPS is converted to EOV.
*Data from ARES-G4 and the topography is read into RES2DINV software.
*An inversion process takes place using forward modeling to obtain a model that best fits the measured pseudo section.
Inversion:
90100110120130140
Ele
va
tio
n (
mB
f)
50 100 150 200 250 300 350 400 450 500 550 600 650
50 100 150 200 250 300 350 400 450 500 550 600 650
90100110120130140
Ele
va
tion
(mB
f)
0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0
1 01 52 02 53 03 54 04 55 05 56 06 57 07 58 08 59 09 51 0 01 0 51 1 01 1 51 2 01 2 51 3 01 3 51 4 01 4 51 5 0
587000
586000
174000Dip ≈1.3°
Dip ≈4.5°
Ωm
120
140
160
Elev
atio
n (m
Bf)
0 200 400 600
0 200 400 600
120
140
160
Elevation (mBf)
0 100res [o h m m ]
200
150
100
50
0
d a y 9 /3
120130140150160
Elev
atio
n (m
Bf)
0 200 400
0 200 400
120130140150160
Elevation (mBf)
0 100res [o h m m ]
300
200
100
0
d ay 5 /12 5 0 m so u th o f th is p o in t
enying5enying4
1 01 52 02 53 03 54 04 55 05 56 06 57 07 58 08 59 09 51 0 01 0 51 1 01 1 51 2 01 2 51 3 01 3 51 4 01 4 51 5 0
80
90
100
110
120
Ele
vatio
n (m
Bf)
0 50 100 150 200 250 300 350 400
0 50 100 150 200 250 300 350 400
80
90
100
110
120
Elevation (m
Bf)
1 01 52 02 53 03 54 04 55 05 56 06 57 07 58 08 59 09 51 0 01 0 51 1 01 1 51 2 01 2 51 3 01 3 51 4 01 4 51 5 0
NOT CONTINUOUS?
585000584000
173000
• Old Pannonian Lake that previously covered the area may have deposited multiple limestone layers and clay/shale in between.
•Shallow marine environment would respond quickly to any climatic changes.
•Deformation causes tilting of layers.
•Differential erosion. (More resistive limestone layers erode more slowly than clay/shale)
>THE INVERSION ESSENTIALLY CREATES A BEST FIT MODEL.
INTERPRETATIONS ARE AMBIGUOUS. (OTHER MEASUREMENTS NEEDED)
NEAR SURFACE RESISTIVITY VARIATIONS CAN MASK THE EFFECTS OF DEEPER VARIATIONS.
THE GPS MEASUREMENTS ARE APPROXIMATELY +/- 5m IN THE (X,Y) PLANE. THE ERROR IN THE (Z) DIRECTION
(ELEVATION) IS ABOUT +/- 10m.
Water level fluctuation -> small lakes, limestone caps on hills at about 120-130m hight above sea level.
The high resistive layer (Enying1 Western end) could be dipping towards the South.
Interpretation without a 3-D Model is very ambiguous.
Fülöp József: Magyarország geológiája – Paleozoikum I.
Gyalog László, Horváth István: A Velencei-hegység és a Balatonfő földtana; Budapest 2004
Lóczy Lajos Geological Map.
M.H.Loke, (1996-2004), (Revision date : 26th July 2004)
Philip Kearey, Michael Brooks, Ian Hill: An introduction to geophysical exploration; Blackwell Publishing Company 2002
Thanks to
Zoltán Hámori for leading the survey
All other groups for sharing their data and results
ELTE Space Research Group for the maps
All the staff of University of Leeds and Eötvös Loránd University