Download The Identification of Seulimeum Fault System in Iejue, Aceh Besar

The Identification of Seulimeum Fault
System in Iejue, Aceh Besar (Indonesia)
by Using Magnetic Method
Muhammad Taqiuddin Zakaria
Postgraduate Student, Geophysics Section, School of Physics, 11800 Universiti
Sains Malaysia, Penang, Malaysia; e-mail: [email protected]
Dr. M.M. Nordiana
Lecturer, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia,
Penang, Malaysia; e-mail: [email protected]
Dr. Rosli Saad
Associate Professor
Senior Lecturer Geophysics Section, School of Physics, 11800 Universiti Sains
Malaysia Penang, Malaysia; e-mail: [email protected]
Dr. I. N. Azwin
Lecturer, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia,
Penang, Malaysia
e-mail: [email protected]
Nur Khairunnisa Aqilah Yunos
Postgraduate Student, Geophysics Section, School of Physics, 11800 Universiti
Sains Malaysia, Penang, Malaysia; e-mail: [email protected]
ABSTRACT
Magnetic is a non-destructive geophysical technique that measure the Earth's magnetic field at
specific location. It has numerous application in engineering and environmental field such as
locating a fault zone. Fault are described as planar or gently curved fracture in a rock mass where
there are significant relative displacement along the fracture as a result from the earth movement.
The purpose of this study is to identify the Seulimeum fault system in Iejue, Aceh Besar
(Indonesia) by using a magnetic method and correlate the result with geological map and also to
understand a trend pattern of fault system. Magnetic survey was conducted with the proton
magnetometer with 50 m interval of each magnetic station (rover). This survey consist of three
difference survey lines with length of 1 km of each line. The magnetic data was processed by
utilizing Microsoft excels and Surfer10 software which was displayed in a form of contouring and
revealed fault zones. The local magnetic value covers from -150 to 600 nT. The result showed a
low residual magnetic value at a north part compared to south part of study area which indicated a
pattern of fault zone. Magnetic residual was successfully correlated with the geological map
which show the existence of the Seulimeum fault in this study area.
KEYWORDS:
Magnetic, Seulimeum fault, Iejue, Aceh Besar
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INTRODUCTION
The Aceh province in Indonesia, located around the Sumatran subduction zone. The Great
Sumatran Fault (GSF) is recorded as dextral strike-slip fault zone which contain a result from the
oblique convergence of the subduction between the Indo-Australian and Eurasian plates (Bellier
et al., 1997). Strike-slip faulting occurs hundred kilometers to the east of the trench and involves
slip directed parallel to the trench which is pass through the Sumatra Island. This fault is
classified into three major sections which are southern, central, and northern (Aydan, 2009). The
Sumatran Fault with 1900 km long structure of the right lateral strike slip is highly segmented and
consists about 20 major segments. Most segment are range in length about 60 to 200 km,
(Natawidjaja and Wahyu, 2007).
From the history of earthquake along Sumatran Fault that has been documented in 1980
shows the correlation of the segmentation of the fault and the location of the earthquake in the
past ruptures (Natawidjaja et al., 2006). The sumatran fault runs length of the Barisan Mountains,
a range uplifted basements blocks, granitic intrusions and Tertiary sediments, topped by TertiaryRecent volcanism. The Sumatran Fault System in Aceh can be classified into two major segments
which are Seulimeum and Aceh fault. Geomorphic features shows the Seulimeum Fault still
active compare to Aceh Fault. This fault cut through Plio-Pleistone sediments and volcanic
product of the active Seulawah Agam volcano and displaces the axial traces of east-west trending
folds. This process cause the Pliocene deposits moved from the southwest side of the fault to
northwestwards (Bennett et al., 1981).
GENERAL GEOLOGY
Aceh is located at northern part of the Sumatra island. There are four major volcanosedimentary sequences, separated by unconformities are identified which is three are pre-Tertiary
in age and others is Tertiary to Recent (Cameron et al., 1980). Sumatran Fault system occurs from
the Middle Miocene and the opening of the Andaman Sea. Pre-Tertiary basements rocks outcrop
mainly along the central spine of the Barisan Mountains, which extend the length of the island
parallel to the southwest cost. Figure 1 shows the regional tectonic setting of sumatra island.
The area from northeast and southwest is overlain by Tertiary sedimentary and volcanic
rocks. Rock unit of all ages are transacted by Sumatran Fault which follow the NW-SE trend
(Barber and Crow, 2003). The geology of Banda Aceh Quadrangle has been mapped (figure 2) by
Bennett et al., 1981. The lithology of the study area, Ieju is dominated by Lam Tuba volcanic
which is composed of andesitic to dacitic volcanic, pumiceous breccia, tuffs, agglomerate and ash
flows with composition of tuffaceous and calcareous sandstones, conglomerates and
mudstones(Bennett et al., 1981). The geological formation formed a topographic depression,
occupied with alluvial flat and low flat-topped hills within Barisan Range (Katili and Hehuwat,
1967; Page et al., 1979). Figure 3 shows the location of Iejue in the google earth.
Vol. 21 [2016], Bund. 02
Figure 1: Regional tectonic setting of Sumatra.
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STUDY AREA
Scale
0km
5km
10km
Figure 2: Redraw and simplify from: Geological Map of Banda Aceh Quadrangle, Sumatra
(Bennett et al. 1981).
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Legend
Geology fault
Figure 3: Location of the study area: Iejue (Google Earth, 2015).
METHODOLOGY
The ground magnetic survey is carried out with proton precession magnetometer device and
Global Positioning System (GPS) navigation for real-time measurements. Three difference survey
line which is L1, L2, and L3 with length of 1 km and 50 m interval of each magnetic station
(rover) is setup in order to identifying the subsurface characteristics. A base station with magnetic
homogeneity is carefully selected to record magnetic reading at time interval 60 seconds for
diurnal correction affected by the Earth's field. Figure 4 and 5 shows the magnetic line and
magnetic station in a survey area. The magnetic data is measured independent grid was later
combined to produced single master grid. This single master grid is processed using Surfer10
software to produced full magnetic map (figure 6). All the magnetic data were corrected for
diurnal variation and IGRF correction to obtain a corrected magnetic anomaly data for mapping
the residual magnetic contour map.
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Legend
ML1 : Magnetic Line 1 ML2 : Magnetic Line 2 ML3 : Magnetic Line 3
Scale: 0m
500m
250m
Figure 4: Magnetic survey line of the study area (Ieju).
Legend
Magnetic station
Figure 5: Magnetic station on a survey line area.
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RESULTS AND DISCUSSION
Magnetic results show lateral view of the faulting system in the study area (Figure 7). The
local magnetic value covers from -150 to 600 nT. The total intensity mangnetic anomaly study
area shows low magnetic value from -150 nT to -50 nT at northwest part while highly magnetic
anomalies from range 200 nT to 450 nT at southeast of study area. The long dislocation from
northwest part to southeast direction of study area is interpreted as geological fault.
Magnetic Residual (nT)
LEGEND
Figure 6: Magnetic anomaly of local residual
LEGEND
Magnetic Residual (nT)
Fault line system
Figure 7: Magnetic anomaly of fault line system.
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CONCLUSION
The magnetic result from this survey shows that a Seulimeum fault trend is from NW-SE
direction and also supported by geological map that suggested there are several small fault exist
in this survey area. From this survey it shows that magnetic method is suitable in determination
and mapping the fault zone beside identify the subsurface characteristic.
ACKNOWLEDGEMENTS
The authors wish to thank to lecturers, technical staffs and all member of Geophysics group,
Universiti Sains Malaysia (USM), Penang, Malaysia, all students and staffs of Faculty of Science,
Universitas Syiah Kuala(UNISYIAH), Banda Aceh (Indonesia) for their assistance during the
geophysical field data acquisition.
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