ダイコウ 【無料健康相談 マッサージベッド 対象製品】【ナビス】丸型

J. Black Sea/Mediterranean Environment
Vol 13:107-114 (2007)
Application of the Talwani modeling method to the
magnetic data of Sinop and its surrounding
Talwani modelleme yönteminin Sinop ve civarının
manyetik verilerine uygulanması
Sinan Demirel* and Fatih Adatepe
İstanbul University, Institute of Marine Sciences and Management, Müşküle
Sokak, 1, Vefa, İstanbul
Abstract
In this study, Talwani modeling method is applied to total magnetic anomaly map of
Sinop and its surrounding area. As a result, the high anomaly values observed in the
map were attributed to volcanic formations. The lower anomaly values were
attributed to the effect of sediment cover. Tectonically structural elements existent
in this area are evaluated as fault anomalies on the profiles in the magnetic map. The
calculated average depth (1.5 - 8 km) values obtained during this model study are
consistent with the former studies.
Keywords: Talwani modeling method, Sinop, magnetic data, fault
Introduction
Sinop is a peninsula in the Black Sea. The offshore part of Black Sea shelf
area ends with -100 m slope in most of the basin as in Sinop (Fig.1). The
shelf is relatively wider in the front part of Sinop and the deployment and
width have a strong relationship with the tectonic structure of posterior rock
and aggregation structures (Erinç, 1984). This region is on the agenda
nowadays, relating to oil and natural gas prospects and possible nuclear plant
establishment.
*
Corresponding author: [email protected]
107
Previous magnetic studies
Some magnetic studies have been executed earlier different researchers
(Tahran, 1987; Yiğiter, 1989; Demirel and Adatepe, 2003; Demirel and
Adatepe, 2006) in areas neighboring the coast of Sinop. In these studies,
master curves were used with one dimensional Fourier analysis, and it is
determined that average depths of masses, which give correspondence to
magnetic anomalies, are between 2 and 8 km. Structure depths of magnetic
masses calculated in the studies done in deeper sea basins of Black Sea, are
determined between 10 and 20 km (Belousov et al., 1988).
Regional geology of Sinop
Great numbers of studies have been done relating the geological evolution of
Black Sea (Saner, 1980; Annon., 1985; Gökaşan, 1996; Yılmaz et al., 1997).
The study done in land and sea areas of Sinop has contributed to the
understanding of local geology of the region (Özhan, 2004). According to
these points, the primal unit of the region is a volcanic formation which is
composed of Upper Crateceous aged agglomerate, basalt lava and dikes. In
Sinop peninsula, Miocene aged sandy limestones are over Upper Crateceous
aged agglomerates (Fig. 1a). In İnceburun peninsula, Plio-Quarternary
sediments composed of fluvial and aeolian origin sands are above the Upper
Crateceous aged volcanic structures (Fig. 1a). The region was under the
effect of compressive forces in the direction of North Northeastern – South
Southwestern between Upper Crateceous – Upper Miocene periods, and at in
the end of Miocene, this activity was decreased by the activity of North
Anatolian Fault (NAF) system (Özhan, 2004). Active lineament in the sea
bottom has been observed in higher differential seismic reflection records of
the same study (Fig. 1a). The reflection characters in the profiles, suggest
that the basic rock under the sea bottom covered with young sediments
belongs to the Upper Crateceous aged old volcanic formations (Fig. 1b) and
also includes faults (Özhan, 2004).
108
N
100
BLAC K SEA
İnce
b uru
n
10
0
SİNO P
U. C reta c eous
Quaternary
Mioc ene
Plio-Quaternary
100
İsobaths(m)
Faults
(a)
SİNO P
N
S
Se a le ve l
Se a le v e l
İnc eb urun
N
S
Sea level
U.Creta ceous
Te r t ia r y
Eocene
M io c e n e
Qua terna ry
Fa u lts
Plio Q u a rte rn a r y
(b)
Figure 1. (a) Regional geology of study area and local faults,
(b) Structural geological profiles (modified from Özhan, 2004)
Material and Method
The total magnetic anomaly map used in this study was prepared by the
Turkish Navy Department of Navigation, Hydrography and Oceanography
(TNDNHO) (Fig. 2). The observed anomalies forming the north and south of
420 N latitude have different characteristics. Positive 100 and 200 nT
contours of the south edge of 420 N latitude increase to positive 500 nT
towards the south, whereas the magnetic values that constitute the north of
the same latitude degrees to negative 200 nT towards the offshore.
109
Taking into consideration the magnetic anomalies which are evaluated
qualitatively from the magnetic map, Talwani modeling method
(Talwani et al., 1959) is applied to the selected three profiles (Fig. 2). The
structural geological profiles (Fig. 1b) which are derived from high
differentiation seismic reflection method have contributed greatly to the
structural model studies (Fig. 3) constituted after application.
0
35
A’
N
B’
-200
C’
0
-200
-1
0
0
+ 10
0
+2
00
0
42
+ 4
00
+ 3 0 0
+ 10 0
+ 2 00
+ 40 0
+ 3
0
+ 4
00
+ 5 00
+ 3
0
A
0
C
0
B
0
2
4
Km
Figure 2. Total magnetic anomaly map (TNDNHO) of study area and profiles
(original scale 1:150 000)
110
( nT )
5 00
400
30 0
20 0
100
0
-1 0 0
O b seve d
C a lc u la te d
-2 20
0
km
1
2
3
4
5
6
7
8
9
S
N
0
1
Derinlik (km)
2
3
4
5
6
7
AA’
( nT )
500
400
Ob served
Ca lcula ted
300
200
100
0
-100
-200
km
0
1
2
3
4
5
6
7
8
9
S
10
N
0
Depth(km)
1
2
3
4
5
6
7
8
BB’
( nT )
15 0
10 0
Ob se rve d
Ca lc ula te d
0
-10 0
-20 0
km
0
1 .5
3
4.5
6
7.5
9
10 .5
12
1 3.5
15
NW
SE
0
Depth(km)
1
2
3
4
5
6
7
8
CC’
Figure 3. Magnetic profiles (AA’, BB’, CC’) and their structural models
111
Discussion and Results
The numerical calculations of structure models which were gained after
application show that the depths of magnetically active masses are between
1.5 and 8 km in average. In addition, the points of evident changes
determined in magnetic profiles were evaluated as fault anomalies (Fig. 3).
The high value of anomaly from shelf offshore area through the coast of
Sinop is an indication of heightening and surfacing through the south of
volcanic unit containing Upper Crateceous-aged and magnetically intensive
material, which was given as a basic rock (Fig. 1). On the contrary, it is
considered that the decrease in magnetic anomaly values to the negative in
the coast offing is caused by sediment cover, which was thickening towards
the abyssal area. In other words, most probably the higher values of
magnetic masses under the sediment cover are masked by sediments.
Another point of issue is that the coastal area of Sinop peninsula is
heightened by the effects of interior forces of the Earth’s crust (Erinç, 1984).
It is determined that current seismic data has not constituted a consistent
activity with Quaternary geology (Annon., 1985; Kirişçioğlu Sancar, 1999).
1. In the qualitative evaluation of magnetic anomaly map, the
existence of the increasing values up to positive 500 nT in the
coastal areas of Sinop, is an indication of volcanic unit
containing Upper Crateceous aged and magnetically consistent
material in the region.
2. In the offshore, it is considered that the magnetic anomaly values are
masked by the effect of thick sediment cover, thus resulting in lover
values.
3. In the Sinop shelf area some tectonic structural components may be
interpreted as a fault. Although this makes the region tectonically
sensitive, an extensive seismic activity has not been detected.
4. As a result of structural model studies, the average depths of
magnetic masses are calculated to be between 1.5 and 8 km. These
are consistent with the results of the previous magnetic studies,
which were obtained by using different methods in the regions near
coastal areas.
112
Özet
Bu çalışmada, Talwani modelleme yöntemi uygulanarak Sinop ve çevresine ait
toplam manyetik anomali haritasının jeofizik analizi yapılmıştır. Buna göre haritada
yüksek anomali gösteren değerlerin volkanik formasyonlardan kaynaklandığı
belirlenmiştir. Düşük anomali değerlerinin ise şelf alanının üst kısmını oluşturan
sediment örtünün etkisinde kaldığı görülmüştür. Manyetik haritadan alınan profiller
üzerinde tektonik anlamda fay anomalisi şeklinde değerlendirilen yapısal unsurlar
gözlenmiştir. Model çalışmalar sonunda elde edilen ortalama derinlik değerleri
(1.5 - 8 km) bölgede daha önce yapılan çalışmalarla uyumludur.
References
Annon. (1985). Karadeniz’in Güney Kenarının Tektonik Karakteristikleri,
İTÜ Maden Fakültesi Jeoloji Bölümü Proje No:TEK-85/53, Türkiye Elektrik
Kurumu Nükleer Enerji Santraller Dairesi, Ankara.
Belousov, V.V., Volvovsk, B.S. (1988). Structure and evolution of the Earth
crust and upper mantle of the Black Sea. Boll. Geof. Teor. Appl.30: 117-118.
Demirel, S. and Adatepe, F. (2003). Karadeniz’in Manyetik Verilerinin
Analizi, İ.Ü. Bilimsel Araştırma Projeleri Yürütücü Sekreterliği, Proje
No:1767/21122001.
Demirel, S. and Adatepe, F. (2006). Examination on the Magnetic Data of
Sinop Shelf Area, The 17. International Geophysical Congressand
Exhibition of Turkey, 14-17 November 2006, Ankara, p.22.
Erinç, S.(1984). Karadeniz Çanağının Jeomorfolojik ve Yapısal Özellikleri
ve Morfometrisi, İstanbul Üniversitesi, Deniz Bilimleri ve Coğrafya
Enstitüsü, BÜLTEN 1: 15-22.
Gökaşan, E. (1996). Anadolu’nun Karadeniz Kıyılarının Neotektoniğine Bir
Yaklaşım, Yerbilimleri 29: 99-109.
Özhan, G. (2004). Sinop Açıklarında Jeolojik ve Aktif Çizgisel Bulgular,
Kıyı ve Deniz Jeolojisi Sempozyumu, 13-15 Eylül 2004, İstanbul. p. 21.
Kirişçioğlu Sancar, A. (1999). Türkiye’nin Karadeniz Kıyılarının
Sismotektonik Değerlendirilmesi, İ.Ü. Deniz Bilimleri ve İşletmeciliği
Enstitüsü, M.Sc. Thesis.
Saner, S. (1980). Batı Pontidlerin ve komşu havza oluşumlarının levha
tektoniği, MTA Dergisi 93-94: 1-20.
113
Tahran, Ü. (1987). Karadeniz Mağnetik profillerine güç spektrumunun
uygulanması ve ortalama derinliklerin saptanması, İ.Ü. Deniz Bilimleri ve
Coğrafya Enstitüsü, M.Sc. Thesis.
Talwani, M., Worzel, J. L. and Landisman, M. (1959). Rapid Gravity
Computations for two-dimensional bodies with application to the Mendocine
Submarine Fracture Zone, J. Geophysical Research 64: 49-61.
Yılmaz, Y., Tüysüz, O., Yiğitbaş, E., Genç, C. and Şengör, A.M.C. (1997).
Geology and Tectonic Evolution of Pontides, in A.G. Robinson (Ed.),
Regional and Petroleum Geology of Black Sea and Surrounding Region,
AAPG Memoir. 68:183-226.
Yiğiter, G. (1989). Karadeniz Mağnetik alan şiddet haritasına tek boyutlu
Fourier ve Master Eğrileri uygulanarak derinlik tayini, İ.Ü.Deniz Bilimleri
ve Coğrafya Enstitüsü. M.Sc. Thesis.
Received: 09.03.2007
Accepted: 23.03.2007
114