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

vatio

n (m

Bf)

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

Eleva

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

Ele

vatio

n (m

Bf)

0 200 400 600

0 200 400 600

120

140

160

Elevation (m

Bf)

0 100res [o h m m ]

200

150

100

50

0

d ay 9 /3

120

130

140

150

160

Ele

vatio

n (m

Bf)

0 200 400

0 200 400

120

130

140

150

160

Elevation (m

Bf)

0 100res [o h m m ]

300

200

100

0

d a y 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

Elevatio

n (mB

f)

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