The effects of the North Anatolian Fault on the geomorphology in the Eastern Marmara Region,Northwestern Turkey

North-western Anatolia has been actively deformed since Pliocene by the right-lateral North Anatolian Fault (NAF). This transform fault, which has a transtensional character in its western end due to effects from the Aegean extensional system, is a major control on the regional geomorphologic evolution. This study applied some geomorphic analyses, such as stream longitudinal profiles, stream length-gradient index, ratio of valley floor width and valley height, mountain front sinuosity, hypsometry and asymmetry factor analyses, to an area just east of the Sea of Marmara in order to understand the tectonic effects on the area’s geomorphological evolution. The active and fastest northern branch of the NAF lies within a topographic depression connecting Sea of Marmara in the east to the Adapazar? Basin in the west. This depression filled with early Pleistocene and younger sediment after a series of pull-apart basins opened along the NAF. North of this depression lies the Kocaeli Peneplain, whose southern edge the NAF uplifted. Meandering streams on the central peneplain were incised possibly due to baselevel changes in the Black Sea. South of the depression, an E-trending mountainous area has a rugged morphology. Based on geomorphic analyses, uplifted Pliocene sediment, marine terraces, and recent earthquake activity, this area between northern and southern branches of the NAF is actively uplifting. The geomorphic indices used in this study are sensitive to vertical movements rather than lateral ones. The bedrock lithology that played an important role on the area’s geomorphologic evolution also affects the geomorphic indices used here.     

Structural relationship between the Sea of Marmara Basin and the North Anatolian Fault Zone

The North Anatolian Fault (NAF) zone is 1500 km long, extending almost up to the Greek mainland in the west. It is a seismically active right-lateral strike-slip fault that accommodates the relative motion between the Turkish block and Black Sea plate. The Sea of Marmara lies along the western part of the NAF and shows evidence of subsidence. In this area pure strike-slip motion of the fault zone changes into extensional strike-slip movement that is responsible for the creation of the Sea of Marmara and the North Aegean basins. The northern half of the Sea of Marmara is interpreted as a large pull-apart basin. This basin is subdivided into three smaller basins separated by strike-slip fault segments of uplifted blocks NE-SW. Basinal areas are covered by horizontally layered sedimentary sequences. Uplifted blocks have undergone compressional stress. All the blocks are subsiding and are undergoing vertical motions and rotations relative to one another. The uplifted blocks exhibit positive Bouguer gravity anomalies. According to gravity interpretation, there is relative crustal thinning under the Sea of Marmara. The northern side of the Sea of Marmara is marked by a distinctive deep-rooted magnetic anomaly, which is dissected and shifted southward by strike-slip faulting. The southern shelf areas of the Sea of Marmara are dominated by short-wavelength magnetic anomalies of shallow origin.     

The Bekten Fault: the palaeoseismic behaviour and kinematic characteristics of an intervening segment of the North Anatolian Fault Zone,Southern Marmara Region,Turkey

The Bekten Fault is 20-km long N55°E trending and oblique-slip fault in the dextral strike-slip fault zone. The fault is extending sub-parallel between Yenice-Gönen and Sar?köy faults, which forms the southern branch of North Anatolian Fault Zone in Southern Marmara Region. Tectonomorphological structures indicative of the recent fault displacements such as elongated ridges and offset creeks observed along the fault. In this study, we investigated palaeoseismic activities of the Bekten Fault by trenching surveys, which were carried out over a topographic saddle. The trench exposed the fault and the trench stratigraphy revealed repeated earthquake surface rupture events which resulted in displacements of late Pleistocene and Holocene deposits. According to radiocarbon ages obtained from samples taken from the event horizons in the stratigraphy, it was determined that at least three earthquakes resulting in surface rupture generated from the Bekten Fault within last ~1300 years. Based on the palaeoseismological data, the Bekten Fault displays non-characteristic earthquake behaviour and has not produced any earthquake associated with surface rupture for about the last 400 years. Additionally, the data will provide information for the role of small fault segments play except for the major structures in strike-slip fault systems.     

Taxonomical and Biogeochemical Investigation of Elements in Holocene Mollusk Shells in the South and Southwestern Marmara Basin,Turkey

Concentrations of some heavy metals and trace elements such as Cr, Ga, Ni, Zn, Mo, Cu, Pb, Yb, Y, Nb, Ti, Sr, Ba, Mn, Sc, Co, V, Zr, Fe, Al, W, Se, Bi, Sb, As, Cd in recent mollusk shells and factors affecting their distribution and deposits collected from various depths in the southern and southwestern parts of the Marmara Sea are investigated. The distribution of the elements in the shells is categorized into four groups. Of these, concentrations of 12 elements （As, Bi, Cd, Co, Ga, Mo, Nb, Sb, Se, Sc, W and Yb） are below zero [（0.053-0.79）×10^-6]; concentrations of seven elements （Cr, Ni, Pb, V, Y, Zr and Cu） are （1.0-6.0）×10^-6; concentrations of four elements （Ti, Mn, Ba and Zn） are 10- 20×10^-6; and concentrations of five elements （Si, Al, Fe, Mg and Sr） are （47.44-268.11）×10^-6. The taxonomic characteristics of the 29 elements were studied separately in mollusk shells such as Chamalea gallina （Linn6）, Pitar rudis （Poli）, Nassarius reticulatus （Linn6）, Venerupis senescens （Coocconi）, Mytilus galloprovincialis （Lamarck）, Mytilaster lineatus （Gemelin in Linne） and Chlamys glabra. It was found that, in mollusk taxonomy, the elements have unique values. In other words, element concentrations in various mollusk shells depend mainly on the taxonomic characteristics of mollusks. In various bionomic environments different element distributions of the same species are attributed to the different geochemical characters of the each environment. Data obtained in this study indicate that the organisms are the most active and deterministic factors of the environment.     

Taxonomical and Biogeochemical Investigation of Elements in Holocene Mollusk Shells in the South and Southwestern Marmara Basin, Turkey

Concentrations of some heavy metals and trace elements such as Cr,Ga,Ni,Zn,Mo,Cu, Pb,Yb,Y,Nb,Ti,Sr,Ba,Mn,Sc,Co,V,Zr,Fe,Al,W,Se,Bi,Sb,As,Cd in recent mollusk shells and factors affecting their distribution and deposits collected from various depths in the southern and southwestern parts of the Marmara Sea are investigated.The distribution of the elements in the shells is categorized into four groups.Of these,concentrations of 12 elements(As,Bi,Cd,Co,Ga,Mo,Nb, Sb,Se,Sc,W and Yb)are below zero [(0.053-0.79)×10~(-6)];concentrations of seven elements(Cr,Ni, Pb,V,Y,Zr and Cu)are(1.0-6.0)×10~(-6);concentrations of four elements(Ti,Mn,Ba and Zn)are 10- 20×10~(-6);and concentrations of five elements(Si,Al,Fe,Mg and Sr)are(47.44-268.11)×10~(-6).The taxonomic characteristics of the 29 elements were studied separately in mollusk shells such as Chamalea gallina(Linné),Pitar-rudis(Poll),Nassarius reticulatus(Linné),Venerupis senescens (Coocconi),Mytilus galloprovincialis(Lamarck),Mytilaster lineatus(Gemelin in Linné)and Chlamys glabra.It was found that,in mollusk taxonomy,the elements have unique values.In other words, element concentrations in various mollusk shells depend mainly on the taxonomic characteristics of mollusks.In various bionomic environments different element distributions of the same species are attributed to the different geochemical characters of the each environment.Data obtained in this study indicate that the organisms are the most active and deterministic factors of the environment.     

山东的南四湖不是断层湖

山东的南四湖位于鲁西南的微山县境,南北长119km,东西平均宽9.2km,最大水深2.76m,平均1.46m,具狭长而水浅的特征。南四湖自南而北依次为微山湖、昭阳湖独山湖和南阳湖,四湖连为一体,实际上是一个湖。黄河南岸的东平湖恰好位于这一狭长湖泊的北延,在这两大湖之间,尚有规模较小的马场湖、蜀山湖和马踏湖断续相连。     

Characteristics of the 1912 co-seismic rupture along the North Anatolian Fault Zone (Turkey): implications for the expected Marmara earthquake

Evidence of right‐lateral offsets associated with the 1912 earthquake (M_w 7.4) along the North Anatolian Fault (Gaziköy–Saros segment) allow us to survey (using DGPS) the co‐seismic and cumulative slip distribution. The damage distribution and surface breaks related with the earthquake show an elongated zone of maximum intensity (X MSK) parallel to the fault rupture on land but this may extend offshore to the north‐east and south‐west. Detailed mapping of the fault using topographic maps and aerial photographs indicates the existence of pull‐apart basins and pressure ridges. At several localities, the average 1912 offset along strike is 3.5–4 m and cumulative slip is 2–6 times that of individual movement. The fault rupture geometry and slip distribution suggest the existence of three subsegments with a combined total length of 110–120 km, a fault length and maximum slip similar to those of the 1999 Izmit earthquake. The amount of slip at the north‐easternmost section and in the coastal region of the Sea of Marmara reaches an average 4 m, thereby implying the offshore extension of the 1912 rupture. The results suggest that the 1912 event generated up to 150 km of surface faulting, which would imply a M_w 7.2–7.4 earthquake and which, added with rupture lengths of the 1999 earthquakes, help to constrain the remaining seismic gap in the Sea of Marmara.     

Evaluation of earthquake potential along the Northern Anatolian Fault Zone in the Marmara Sea using comparisons of GPS strain and seismotectonic parameters

Seismotectonic parameters including the Gutenberg-Richter b-value and multifractal dimensions D₂ and D₁₅ of seismicity patterns (both spatial and temporal) were compared to GPS-derived maximum shear and dilatation strains measured in the Marmara Sea region of western Turkey along the Northern Anatolian Fault Zone (NAFZ). Comparisons of seismotectonic parameters and GPS-derived maximum shear and dilatation strain along the NAFZ in the vicinity of the 1999 M7.4 Izmit earthquake reveal a positive correlation (r = 0.5, p = 0.05) between average dilatation and the Gutenberg-Richter b-value. Significant negative correlation (r = − 0.56, p = 0.03 and r = − 0.56, p = 0.02) was also observed between the spatial fractal dimension D₂ and GPS-derived maximum geodetic and shear strain. This relationship suggests that, as maximum geodetic and shear strains increase, seismicity becomes increasingly clustered.Anomalous interrelationships are observed in the Marmara Sea region prior to the Izmit event along a bend in the NAFZ near the eastern end of the Marmara Sea known as the Northern Boundary Fault (NBF). An asperity is located near the northwest end of the NBF. Along the 50-km length of the NBF, GPS strains become slightly compressive. The correlation between b-value and GPS-derived dilatation suggests that regions in compression have increased probability of larger magnitude rupture. The NBF appears to serve as an impediment to the transfer of strain from east to west along the NAFZ. Recurrence times for large earthquakes along the NBF are larger than in surrounding areas. Temporal clustering of seismicity in the vicinity of the NBF may represent foreshocks of an impending rupture.     

琼东南盆地断裂活动性定量计算及其发育演化模式

在地震剖面解释的基础上,运用断层活动速率法和位移-距离法对琼东南盆地主要断裂系统的活动性进行了定量计算。结果表明,断裂的活动性与盆地的演化阶段相对应,同时可以在同裂陷阶段划分出始新世-早渐新世裂陷幕和晚渐新世断坳转换幕,这两幕裂陷控制了盆地深部的基本构造格局。单条断层在早渐新世至晚渐新世期间断裂主要活动中心存在由东向西迁移的过程,盆地断裂系统活动中心在晚渐新世至早中新世也存在由东向西迁移的过程,盆地内规模较大的复合断裂带具有区段式活动的特征。将盆地内断裂系统发育模式总结为两种：以6号和11号断裂带为代表的简单生长模型,断裂系统发育演化过程中表现为单一区段断层独立生长的特征,断层简单地由中间向两侧生长,断层位移距离曲线自始至终为半椭圆型,且最大位移大致位于断层中部;以2号和5号断裂带为代表的生长连通型生长模式,断裂带由多条区段式活动的断层生长连接形成,其生长发育过程表现为沿断层面纵向上最大滑移量由各个区段的中心向各个区段交汇处迁移,由此各个区段断端破裂扩展,最终相互连接而形成一条大型断裂带。     

From transpression to transtension: changes in morphology and structure around a bend on the North Anatolian Fault in the Marmara region

The east–west-trending North Anatolian Fault makes a 17° bend in the western Marmara region from a mildly transpressional segment to a strongly transtensional one. We have studied the changes in the morphology and structure around this fault bend using digital elevation models, field structural geology, and multi-channel seismic reflection profiles. The transpression is reflected in the morphology as the Ganos Mountain, a major zone of uplift, 10 km wide and 35 km long, elongated parallel to the transpressional Ganos Fault segment west of this bend. Flat-lying Eocene turbidites of the Thrace Basin are folded upwards against this Ganos Fault, forming a monocline with the Ganos Mountain at its steep southern limb and the flat-lying hinterland farther north at the flat limb. The sharp northern margin of the Ganos Mountain coincides closely with the monoclinal axis. The strike of the bedding, and the minor and regional fold axes in the Eocene turbidites in Ganos Mountain are parallel to the trace of the Ganos Fault indicating that these structures, as well as the morphology, have formed by shortening perpendicular to the North Anatolian Fault. The monoclinal structure of Ganos Mountain implies that the North Anatolian Fault dips under this mountain at 50°, and this ramp terminates at a decollement at a calculated depth of 8 km. East of this fault bend, the northward dip of the North Anatolian Fault is maintained but it has a normal dip-slip component. This has led to the formation of an asymmetric half-graben, the Tekirdağ Basin in the western Sea of Marmara, containing a thickness of up to 2.5 km of Pliocene to Recent syn-transform sediments. As the Ganos uplift is translated eastwards from the transpressional to the transtensional zone, it undergoes subsidence by southward tilting. However, a morphological relic of the Ganos uplift is maintained as the steep northern submarine slope of the Tekirdağ Basin. The minimum of 3.5 km of fault-normal shortening in the Ganos Mountain, and the minimum of 40 km eastward translation of the Ganos uplift indicate that the present fault geometry has existed for at least the last 2 million years.     

论犬陆地壳断裂拗陷带中的华南型块状硫化物矿床

我国东南部后加里东隆起区之间,分布着若干重要的海西—印支期海相断裂拗陷带(图1)。如长江中下游、钱塘江—信江—萍乡—乐平、闽西南—粤东和韶关—四会—吴川等,这     

Asymmetric slip partitioning in the Sea of Marmara pull‐apart: a clue to propagation processes of the North Anatolian Fault?

Between 1939 and 1999 the North Anatolian fault (NAF) experienced a westward progression of eight large earthquakes over 800 km of its morphological trace. The 2000-km-long North Anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale (∼10 Myr). The Sea of Marmara is a large pull-apart that appears to have been a geometrical/mechanical obstacle encountered by the NAF during its propagation. The present paper focuses on new high-resolution data on the submarine fault system that forms a smaller pull-apart beneath the Northern Sea of Marmara, between two well-known strike-slip faults on land (Izmit and Ganos faults). The outstandingly clear submarine morphology reveals a segmented fault system including pull-apart features at a range of scales, which indicate a dominant transtensional tectonic regime. There is no evidence for a single, continuous, purely strike-slip fault. This result is critical to understanding of the seismic behaviour of this region of the NAF, close to Istanbul. Additionally, morphological and geological evidence is found for a stable kinematics consistent both with the long-term displacement field determined for the past 5 Myr and with present-day Anatolia/Eurasia motion determined with GPS. However, within the Sea of Marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull-apart. The loading associated with the westward propagation process of the NAF may have provided a favourable initial geometry for such a slip separation.     

Basin progress: active deformation analysis by tectonostratigraphic elements and geophysical methods on North Anatolian Fault System (Eastern Marmara Region,Turkey)

Natural Hazards - The Northern Branch of the North Anatolian Fault System controls and deforms the Izmit Basin and the Sapanca Lake Basin in the study area. Unlike the Sapanca Lake Basin, the...     

The sources of metal contents in the shelf sediments from the Marmara Sea, Turkey

The shelf area is the largest morphological unit of the Marmara Sea and is subjected to increasing population, urbanization, and industrial activities. Metal contents (Al, Fe, Mn, Cu, Pb, Zn, Ni, Cr, Co and Hg) of the surface sediments from the shelf areas of the Marmara Sea generally do not indicate shelf-wide pollution. The variability of the metal contents of the shelf sediments is mainly governed by the geochemical differences in the northern and southern hinterlands. Northern shelf sediments contain lower values compared to those of the southern shelf, where higher Ni, Cr, Pb, Cu and Zn are derived from the rock formations and mineralized zones. However, besides from the natural high background in the southern shelf, some anthropogenic influences are evident from EF values of Pb, Zn and Cu, and also from their high mobility in the semi-isolated bay sediments. Anthropogenic influences are found to be limited at the confluence of Istanbul Strait in the northern shelf. However, suspended sediments along the shallow parts of the northern shelf were found to be enriched in Pb and Hg and to a lesser degree in Zn, reflecting anthropogenic inputs from Istanbul Metropolitan and possibly from the Black Sea via the Istanbul Strait.     

焦家断裂带紫罗姬家以南的延伸问题探讨

焦家断裂带是胶西北地区三大著名的金成矿带之一,一般认为焦家断裂带为龙（口）莱（州）断裂带南段的高家庄子紫罗姬家段。根据近几年的研究成果,认为焦家断裂带在紫罗姬家以南,沿195＆#176;～200＆#176;方位延伸至紫罗綦家与黄家之间分为3支：第一分支沿紫罗綦家—赵官庄—前单家—张家埠至曹家埠村北;第二分支（主断裂带）沿紫罗綦家村东南—大尹家—西尹—西罗台村南至曹家埠村南;第三分支自紫罗綦家与黄家村之间向南延伸至史家村西之后,再向南去向不明,推测逐渐尖灭的可能性较大。     

六盘山东麓断裂南段断裂沟槽韵律沉积特征对最新活动时代的限定

六盘山位于华北断块西部鄂尔多斯块体与青藏块体祁连断褶带之间的构造转换部位。前人对六盘山东麓断裂南段进行过一定程度的研究,根据地貌特征推断六盘山东麓断裂南段晚更新世以来不活动。根据断裂特征,大致可将六盘山东麓断裂划分为北段、中段和南段。活动断裂带上的断裂沟槽沉积物表现为由多个粗粒层与细粒层交替的韵律层序结构,韵律沉积特征与断裂活动有直接关系。在六盘山东麓断裂南段冶家村西发现一个断裂沟槽韵律沉积剖面,共鉴别出三期韵律沉积组合。通过分析认为本剖面所反映的韵律沉积特征应为构造成因。对断裂沟槽沉积物采样测年的结果表明,该段断层分别在约500 a BP后、6 ka BP后和15 ka BP前有过明显的地质活动。确认六盘山东麓断裂南段晚更新世以来有过多次活动,是一条活动断裂带。     

Long-term seismicity of Istanbul and of the Marmara Sea region

We examine the long-term seismicity of the Marmara Sea region in Turkey over a period of twenty centuries to attempt to answer two questions: (1) how well recorded in history is the earthquake activity of this region? and (2) does seismicity over this long period of time differ from that over the present century? We study this densely-populated and fast-developing region because it is one of the most tectonically active regions on the continents that appears today to be relatively quiescent.     

Seismic behaviour of the North Anatolian Fault beneath the Sea of Marmara (NW Turkey): implications for earthquake recurrence times and future seismic hazard

Possible long-term seismic behaviour of the Northern strand of the North Anatolian Fault Zone, between western extreme of the 1999 İzmit rupture and the Aegean Sea, after 400 AD is studied by examining the historical seismicity, the submarine fault mapping and the paleoseismological studies of the recent scientific efforts. The long-term seismic behaviour is discussed through two possible seismicity models devised from M _S ≥ 7.0 historical earthquakes. The estimated return period of years of the fault segments for M1 and M2 seismic models along with their standard deviations are as follows: F4 segment 255 ± 60 and 258 ± 12; F5 segment 258 ± 60 and 258 ± 53; F6 segment 258 ± 60 and 258 ± 53; F7 segment 286 ± 103 and 286 ± 90; F8 segment 286 ± 90 and 286 ± 36. As the latest ruptures on the submarine segments have been reported to be during the 1754–1766 earthquake sequence, and the 1912 mainshock rupture has been evidenced to extend almost all over the western part of the Sea of Marmara, our results imply imminent seismic hazard and, considering the mean recurrence time, a large earthquake to strike the eastern part of the Sea of Marmara in the next two decades.