1. Amin KHALIL, Nawawi MOHD, John KAYODE, Saheed ISHOLA
Application of Integrated Geophysical Surveying for Modelling Hot Spring Aquifer at Sungai Klah, Perak, Malaysia
Amin KHALIL, Nawawi MOHD, John KAYODE, Saheed ISHOLA
Universiti Sains Malaysia, 11800USM, Pinang, Malaysia.

2. Objectives
Explore the depth and distribution of geothermal aquifer with target depth of < 300 m. (This depth dependent on previous investigation.
Obtain model for shallow depth structures that may control water migration to the surface,

3. Introduction Sungkai area is famous for its hot spring resort.
Concerns are erupted as the abundance of water resources to develop the area.
Geothermal energy plant was also proposed which also require detailed assessments of the aquifer.
Multi-Geophysical methods are applied to answer the concerns.
The depth of investigation was limited to 300 m based on previous geophysical study.

4. Applied Geophysical Methods
1- Seismic Methods
2- TEM (transient electromagnetic)
3- Gravity method
4- Geomagnetic method

5. Agenda Model of Geothermal aquifer Geologic Setting of the area
Seismic Method
TEM method
Gravity
Geomagnetism
Summary and conclusion.

6. Figure 2: A model of an idealised geothermal system modified after Geothermal 2015

7. Geological and Structural Setting of Sungai Klah
The area is bounded by Granitic intrusion (pink colour) to the northeast. Surface geology is mainly schist and Phyllite from the paleozoic age. As seen in the map, the vicinity of the Sungai Klah possesses number of fault traces (source: Sime Darby, Perak)

8. Seismic surveying Two techniques were used:
1- Optimum offset seismic reflection
2- MASW

9. Instrumentation

10. Seismic Reflection Profile
Raw profile
Location
Felda Complex

11. Processing flow-chart
Pullan et al, 1991.

12. Software Used for analysis
In the present work we used two open source and free softwares. These softwares are:
1- Obspy: Python suite for seismological applications. We used OBSPY to convert the SEG2 format of the field recordings into SEG-Y files.
2- Seismic Unix (SU) to process the data. SU is used under UBUNTU in the present study.

13. Processed Profile Distance (m)
Possible water saturation region at about 100 m depth
TWT (sec)

14. MASW
MASW technique uses the dispersion characteristics of surface waves to determine subsurface shear wave velocity. The technique requires identification of the dispersion curve of surface. Dispersion curve represents the change of velocity with frequencies. The non linear inversion of this curve yield S-wave velocity.

15. Line Location Line 1 Line 2
Two 2-D MASW profiles are carried out. The length of both is 23 m. The geophone interval is 1 m. The source offset is set to 20 m. The recording length is 0.8 sec.
Line 1
Line 2

16. Model
Line 1
In this line we observe too small S-velocity down to depth of 5 m which may represent high water saturation. Then the velocity increase rapidly to almost 400 m/s. Two interesting features are observed. The first one is possible cavity or void (Sv= m/s). This void is associated with possible fault.

17. Line 2
This line is located near the surface occurrence of hot spring. It shows what may be interpreted as shear zone. This shear zone may represent the structure controlling hot water path to the surface.

18. TEM Survey
Five profiles were conducted in the area. The first two lines are in the same straight line, hence we analysed as one extended line. In this presentation two lines are presented. Line 1 and line 5. Line 5 is located south of the hot spring area. Loop size used is 96 x 96 m with single loop layout.

19. Line 1 (extended line)
Corrected decay curves
Inversion Model using

20. Corrected decay curves
Line 5
Corrected decay curves
Inversion Model using
Moderate resistivity
Low resitivity

21. Sungai Klah Hot springs Gravity Data Interpretations

22. Figure: Bouguer anomaly map of the study area

23. The gravity data was obtained using Scrintex CG-2 and CG-5 gravity meter.
The stations selected for measurement of the Gravity data at a relative interval of 25m due to the conditions of land use at the Sungai Klah Hot springs site.
The principal objective of applying gravity method is to define the subsurface structures that affect the area.
From the Figure, it is obvious that the structures beneath the hot springs possesses higher gravity values.

24. These values represent positive density contrast that may be interpreted qualitatively as an intrusion on the Bouguer Anomaly Map.
3-D Euler Deconvolution technique was applied For quantitative modeling of the subsurface structures.
The Euler Deconvolution has the ability to delineate contacts and sources for subsurface anomalies thereby making it a powerful technique for estimating the depth and the geometry of the buried geologic sources.

25. Figure : Euler Deconvolution model of the gravity data around the study area.

26. The lowest value of 16mGal was mostly recorded at the central part, the nearly N-S and E-W directions.
The highest value of 28mGal was recorded around the villa as shown in the map.
Two main structural trends was observed present in the area.
The first trend seems to be dominant roughly in the E-W direction, whilst the other trend is nearly N-S direction.
At the eastern border of the hot spring area, we have relatively deep N-S trend that achieved depth of about 100m.

27. These trends were interpreted to represent the pathway for the underground hot water to go up to the surface.

28. Sungai Klah Hot springs Geomagnetic Data Interpretations
The method was applied in the same pattern as the gravity method during the fieldwork around Sungai Klah Hot springs.
Opposite to the gravity anomaly, we observed lower susceptibility underneath the hot spring area.
This could be due to the subsurface heating.
For quantitative modeling, Reduction to the Pole (RTP) filter and Euler Deconvolution were applied to the data as shown in Figure X.

29. Figure X: Ground magnetic map of the study area.

30. Magnetic residual maps reveal much more detailed subsurface geologic features in particular, the geometry and configuration of individual basement blocks.
The method brings out the subtle magnetic anomalies that result from the changes in rock types across the basement block boundaries.
The presence of a fault is a common interpretation of a magnetic increase or decrease.
The study area present total magnetic intensity (TMI) values that varied from high to very low along the north-south directions.

31. The lowest value of about -600nT was recorded at;
i) the car park,
ii) back of the ticketing office,
iii) by the entrance to the gate of the hot springs and also,
iv) at the entrance to the overhead water tank
as shown in Figure X .
On the other hand, the highest value of about 450nT was recorded in the;
i) villa area,
ii)) office complex area, and
Iii) motor race area.

32. Figure X: RTP and 3-D Euler Deconvolution model of the study area.

33. The model shows that we have nearly the same subsurface structural trends as obtained from the gravity model.

34. Conclusion
Geophysical techniques applied show that the shallow depths is dominated by low resistivity. Low resistivity are also observed near the surface in areas where no hot spring is likely to be there.
The presence of schist and weathered Granite with resistivity as low as 20 ohm.m and < 1 ohm.m respectively lead us to believe that the aquifer is far below.
Seismic reflection showed the possible presence of water saturated layer near the hot spring at a depth of 100 m. This may be interpreted as water accumulation but not the aquifer because the horizontal extent is about 170 m.

35. Conclusion (cont.)
Gravity and geomagnetism showed the existence of faults that are conjugate in the trends of NW-SE and NE-SW. The presence of these faults near hot spring may represent the structures controlling water flow to the surface.
Gravity analysis using Euler deconvolution showed the presence of Granitic intrusion under the hot spring area.

36. Conclusion (cont.)
The question remain what is the depth of the aquifer? Rough estimate using geothermal gradient in hydrocarbon provinces nearby, assuming also the heat flow density is nearly the same can be obtained. Surface temperature of water is almost 99 ̊C, where geochemical analysis pointed out aquifer temperature is almost 145 ̊ C. Hence the loss of temperature is almost 46 ̊ C. Geothermal gradient nearby is 4-6 ̊ per 100 m. Hence the depth to the aquifer could be larger than 800 m. From other similar cases the aquifer is at depth ranging from 1-3 Km.

37. Recommendations
Apply Deep geophysical surveying like MT, gravity and seismic interferometry.
Apply geothermal study to estimate both the heat flow density HFD and geothermal gradient. This may answer two important questions; Why hot springs occur at this specific locations? And what is the expected depth of the aquifer?

38. References