Earthquake hazard in Marmara Region, Turkey

Earthquake hazard in the Marmara Region, Turkey has been investigated using time-independent probabilistic (simple Poissonian) and time-dependent probabilistic (renewal) models. The study culminated in hazard maps of the Marmara Region depicting peak ground acceleration (PGA) and spectral accelerations (SA)'s at 0.2 and 1 s periods corresponding to 10 and 2% probabilities of exceedance in 50 yrs. The historical seismicity, the tectonic models and the known slip rates along the faults constitute the main data used in the assignment. Based on recent findings it has been possible to provide a fault segmentation model for the Marmara Sea. For the main Marmara Fault this model essentially identifies fault segments for different structural, tectonic and geometrical features and historical earthquake occurrences. The damage distribution and pattern of the historical earthquakes have been carefully correlated with this fault segmentation model. The inter-event time period between characteristic earthquakes in these segments is consistently estimated by dividing the seismic slip estimated from the earthquake catalog by the GPS-derived slip rate of 22±3 mm/yr. The remaining segments in the eastern and southern Marmara region are also identified using recent geological, geophysical studies and historical earthquakes. The model assumes that seismic energy along the segments is released by characteristic earthquakes. For the probabilistic studies characteristic earthquake based recurrence relationships are used. Assuming normal distribution of inter-arrival times of characteristic earthquakes, the ‘mean recurrence time’, ‘covariance’ and the ‘time since last earthquake’ are developed for each segment. For the renewal model, the conditional probability for each fault segment is calculated from the mean recurrence interval of the characteristic earthquake, the elapsed time since the last major earthquake and the exposure period. The probabilities are conditional since they change as a function of the time elapsed since the last earthquake. For the background earthquake activity, a spatially smoothed seismicity is determined for each cell of a grid composed of cells of size 0.005°×0.005°. The ground motions are determined for soft rock (NEHRP B/C boundary) conditions. Western US-based attenuation relationships are utilized, since they show a good correlation with the attenuation characteristics of ground motion in the Marmara region. The possibility, that an event ruptures several fault segments (i.e. cascading), is also taken into account and investigated by two possible models of cascading. Differences between Poissonian and renewal models, and also the effect of cascading have been discussed with the help of PGA ratio maps.     

A first deep seismic survey in the Sea of Marmara: Deep basins and whole crust architecture and evolution

Increased source strength, streamer length and dense spatial coverage of seismic reflection profiles of the SEISMARMARA Leg 1 allow to image the deep structure of the marine North Marmara Trough (NMT) on the strike-slip North Anatolian Fault (NAF) west of the destructive Izmit 1999 earthquake. A reflective lower crust and the Moho boundary are detected. They appear upwarped on an E-W profile from the southern Central Basin eastwards, towards more internal parts of the deformed region. Thinning of the upper crust could use a detachment suggested from an imaged dipping intracrustal reflector that would allow upper crustal material to be dragged from beneath it and above the lower crust, accounting for the extensional component but also southwest motion of the southern margin of the NMT. Sections across the eastern half of the NMT, crossing the Cinarcik and Imrali basins, reveal several faults that are active reaching into the basement and have varying strike and proportions of normal and strike-slip displacement. They might be viewed as petals of a large scale negative flower-structure that spreads over a width of 30 km at surface and is rooted deeper in the lithosphere. Under the Central Basin a very thick sediment infill is revealed and its extensional bounding faults are active and imaged as much as 8 km apart down to 6 km depth. We interpret them as two deep-rooted faults encompassing a foundering basement block, rather than being merely pulled-apart from a jog in a strike-slip above a décollement. The deep-basin lengthening would account for only a modest part of the proposed 60 km finite motion since 4 Myr along the same direction oblique to the NMT that sidesteps the shear motion from its two ends. Thus differential motion occurred much beyond the deep basins, like subsidence involving the NMT bounding faults and the intracrustal detachments. The complex partitioned motion localized on active faults with diverse natures and orientations is suggested to represent the overburden deformation induced from horizontal plane simple shear occurring in depth at lithospheric scale, and in front of the North Anatolian Fault when it propagated through the region.     

Late Cenozoic stress states around the Bolu Basin along the North Anatolian Fault, NW Turkey

This study defines the Late Cenozoic stress regimes acting around the Bolu Basin along the North Anatolian Fault in northwestern Turkey. The inferred regional stress regime, obtained from the inversion of measured fault-slip vectors as well as focal mechanism solutions, is significant and induces the right-lateral displacement of the North Anatolian Fault. The field observations have also revealed extensional structures in and around the Bolu Basin. These extensional structures can be interpreted as either a local effect of the regional transtensional stress regime or as the result of the interaction of the fault geometries of the dextral Duzce Fault and the southern escarpment of the North Anatolian Fault, bordering the Bolu Basin in the north and in the south, respectively.The inversion of slip vectors measured on fault planes indicates that a strike-slip stress regime with consistent NW- and NE-trending σ_Hmax(σ₁) and σ_Hmin(σ₃) axes is dominant. Stress ratio (R) values provided by inversion of slip vectors measured on both major and minor faults and field observations show significant variations of principal stress magnitudes within the strike-slip stress regime resulting in older transpression to younger transtension. These two stress states, producing dextral displacement along NAF, are coaxial with a consistent NE-trending σ₃ axis. The earthquake focal mechanism inversions confirm that the transtensional stress regime has continued into recent times, having identical horizontal stress axis directions, characterized by NW and NE-trending σ₁ and σ₃ axes, respectively. A locally consistent NE-trending extensional, normal faulting regime is also seen in the Bolu Basin. The stress-tensor change within the strike-slip stress regime can be explained by variations in horizontal stress magnitudes that probably occurred in Quaternary times as a result of the westward extrusion of the Anatolian block.     

漳州盆地及其邻区地壳深部结构的探测与研究

漳州盆地及其邻区地处我国大陆东南沿海地震带中段。通过该地区高分辨率折射及宽角反射，折射地震探测剖面，获得了该区地壳几何结构与速度结构、地壳深浅部断裂的几何形态和构造关系等。结果表明，该区地壳分为上地壳和下地壳。上地壳的厚度为16．5～18．8km，下地壳厚度为12．0～13．0km。上地壳分为上下两部分。在上地壳下部有一个低速层，速度约为6．00km／s，低速层顶面深度为12．0km左右，厚度约为5．0km。下地壳也分为上下两部分。Moho界面的深度为29．0～31．8km。该区6条地壳浅部正断层大部分向地下延伸深度不超过4km，最大延伸深度达5km左右。据推测，浅部正断层下方有一条高倾角地壳深断裂带，该断裂带向下断至Moho面，向上断至上地壳下部低速层中。深浅部断裂构造不相连接。漳州盆地深浅部构造组合特征表明，九龙江断裂带是该区内一条特征明显、具有复杂深浅构造背景的深断裂带。这一深地震探测成果的获得，使得该地区深部资料解释的可靠性和探测精度比以往显著提高；对深浅部构造的组合可作统一解释，地壳的分层和结构特征更为确切和精细；首次发现上地壳的拉张性构造及铲式正断层组合特征，不仅有助于对漳州及其邻区地震危险性的综合判定，而且对深化东南沿海地震带深部动力学过程的认识具有重要意义。     

Deformational behaviour of continental lithosphere deduced from block rotations across the North Anatolian fault zone in Turkey

Theoretical considerations of lithosphere deformation across transform plate boundaries predict an expression in terms of 3istributed deformation. The magnitude of rotation is expected to diminish away from the fault zone in a way which depends on the length of the fault, the amount of displacement, and the ductility of the lithosphere. Palaeomagnetic studies across the North Anatolian transform fault zone, which separates the Eurasian Plate and Anatolian Block in northern Turkey, show that clockwise rotations predicted from the sense of dextral motion are indeed present and have attained finite rotations of up to 270° during the 5 Ma history of Neotectonic deformation. Such rotations are, however, confined to narrow ( 10 km wide) zones between system-bounding faults and appear to have resulted from rotation in ball-bearing fashion of equidimensional blocks a few kilometres in size. Outside of this zone only anticlockwise rotations are observed; these are unrelated to deformation across the fault zone and record regional anticlockwise rotation of Turkey which is complementing clockwise rotation of Greece and accompanying Neogene opening of the Aegean Sea. The observed behaviour of continental lithosphere satisfies no plausible value of power law behaviour. We therefore conclude that relative motion across this transform boundary occurs as a discrete zone of intense deformation within a brittle layer comprising the seismogenic upper crust. This is presumed to be detached from a continuum deformation response to shearing in the lower crust and mantle beneath.     

The Marmara Sea region: Seismic behaviour in time and the likelihood of another large earthquake near Istanbul (Turkey)

The North Anatolian Fault (NAF) extends for about 1500 km from Karliova to the east, to the Egean Sea in the west. The Marmara region, located near the western end of the NAF, is a tectonically active zone characterized by the transition between a strike slip stress regime and an extensional one in the Aegean Sea. Microseismic studies performed around the Marmara Sea in 1995 [Tectonophysics 316, 2000, 1], and just before the 1999 Izmit Earthquake Bull. Seism. Soc. Am. 92, 2002a, 361;J. Seismol. 6, 2002b, 287) permitted the analysis of the evolution of seismicity connected to this destructive earthquake and its sequels. Several observations indicate that the aftershock distribution fits well the EW orientation of the NAF, but the ruptures are not simple and linear as a first glance would suggest. Instead they are segmented in at least five pieces as shown by the slip variation and aftershock clusters, showing complexity at different scales (Bull. Seism. Soc. Am. 92, 2002a, 361). There is still a gap, across the northern border of the Marmara Sea that has not ruptured, and this is the only sector that did not break on the NAF since the 1939 great Erzincan earthquake. Will it rupture as a whole with a large magnitude earthquake, or by segments with smaller magnitude events? The Hurst analysis of the overall behaviour of the seismicity in the Marmara region since historical times shows that if a large earthquake occurs in the near future, it might break the complete gap. The Hurst character of the time variation of seismicity is persistent with H= 0.82. The aftershocks of the 1999 Izmit earthquake can be analyzed by using the Hurst method, showing an exceptionally high persistent memory.     

Loss estimation in Istanbul based on deterministic earthquake scenarios of the Marmara Sea region (Turkey)

The rapid urban development in Istanbul has lead to an increase in the exposure levels of the urban vulnerability. Due to the steadily increasing population, with improper land-use planning, inappropriate construction techniques and inadequate infrastructure systems, associated with an existing high hazard level, Istanbul is one of the most risky cities in the Mediterranean region. Estimations of casualties and losses, expected for given earthquake scenarios, are necessary to develop sustainable rehabilitation programs and for improving preparedness. Deterministic hazard scenarios and time-dependent probabilistic hazard assessment were used as input to a GIS-based loss estimation model, to evaluate the earthquake risk for Istanbul.     

用DSS资料研究首都圈地区的地壳结构

利用几种不同的一维反演方法对天津-北京-赤城剖面的DSS（deep seismic sounding）数据进行了处理．结果显示：沿剖面基底面北浅南深,但C界面和M界面北深南浅,存在镜像关系：地壳平均速度华北盆地较低,燕山下方较高;燕山隆起和华北盆地的交界处曾多次发生过5．0级以上地震。且在该过渡带上,多条深大断裂成北北东、北东向穿过该剖面,推断首都圈地区地震的发生与莫霍面的局部隆起、速度结构的急剧变化以及深大断裂的存在具有密切关系。     

Determining and modeling tectonic movements along the central part of the North Anatolian Fault (Turkey) using geodetic measurements

The North Anatolian Fault (NAF), which extends from Karl?ova in Eastern Turkey to the Gulf of Saros in the Northern Aegean Sea, is one of the longest active strike-slip faults in the world with a length of about 1500 km. Within the North Anatolian Shear Zone (NASZ) there are long splays off the main trunk of the NAF veering towards the interior parts of Anatolia. Although the whole shear zone is still seismically active, the major seismicity is concentrated along the main branch of the NAF. Splays of the NAF dissect the shear zone into different continental blocks. The largest splay of the NAF was selected to analyze the distribution of movements between the faults delimiting these blocks. Four years of GPS measurements and modeling results indicate that the differential motion between the Anatolian collage and the Eurasian plate along the central part of the NAF is partitioned between fault splays and varies between 18.7 ± 1.6 and 21.5 ± 2.1 mm/yr with the main branch taking ∼90% of the motion.     

黄土高原及邻区地壳P波速度结构

利用地震波走时联合反演算法(改进型最短路径算法)进行三维弯曲地震射线追踪正演,以及共轭梯度法求解带约束的阻尼最小二乘问题进行反演,同时更新速度模型和地震震中位置,结合地方震和区域地震走时资料得到了黄土高原(含汾渭断陷盆地)及邻区地壳三维P波速度结构.其横向变化结果表明,研究区地壳内的P波高速异常区与其内的地震活动构造带相一致,地震多发生在P波高速异常区的边缘或高、低速异常区的交汇处.秦岭山区和鄂尔多斯块体东南区为P波低速异常区.而垂向变化结果则表明研究区存在低速异常区.     

华北北部地区地壳三维P波速度结构的双差地震层析成像

利用区域固定台站和华北科学探测台阵记录的10 461个近震事件的183 909个Pg波绝对走时和495 753个相对走时数据,采用双差地震层析成像获得华北北部(37.5°～41.5°N,111.5°～119.5°E)范围内的地壳三维P波速度结构模型。结果表明:研究区内各主要构造单元具有明显不同的速度结构特征,速度异常的走向与区域构造的走向一致,浅层速度图像很好地反映了地表地质和岩性的变化;重定位后的大部分地震集中在0～20km的深度上,主要位于低速区的内部或高速和低速区的交界部位;三河—平谷和唐山地震震源区中、下地壳的低速异常可能是流体的显示。结合前人成果和本文模型所揭示的深、浅结构,我们认为太平洋板块在中国东部之下的俯冲和滞留引起板块脱水、软流圈物质上涌等一系列过程,软流圈热物质到达上地幔顶部并沿超壳断裂上侵进入地壳,致使上地幔顶部和下地壳中的含水矿物发生脱水作用产生流体,流体继续上移造成中、上地壳发震层的弱化,从而导致大地震的发生。因此华北北部地区的强震活动,以及地壳结构的非均匀性应是与太平洋板块俯冲、滞留引起的深部过程密切相关的。     

Exploration and Research of Deep Crustal Structures in the Zhangzhou Basin and Its Vicinity

INTRODUCTIONThe Zhangzhou basinislocated onthe southeast coast of Fujian Province .Interms of geotectonicunits ,it lies in the east Fujian volcanic fault-depression zone between the Wuyi-Daiyun mountainupheaval zone and depression zone of Taiwan Straits of the south China block. In terms ofseismotectonics ,it islocatedinthe middle sectionof the southeasterncoastal seismic zone .In history,the area was influenced by repeated destructive earthquakes , and the seismic activity was closely…     

乳山震群震源区地壳速度结构初步研究

运用距离乳山震群最近的乳山台2011-2014年远震波形资料,计算接收函数,确定震群震源区及邻近区域的地壳厚度和波速比。结果显示：乳山台下方各个方位的接收函数差异比较大,地壳速度结构呈现横向非均匀性;震源区与邻近区域存在明显差别,邻近区域的中、下地壳存在明显的高速区,震源区中下地壳中存在明显的低速区;震群中M_L3.0以上地震基本发生在高低速交界处。据此推断,乳山震群可能是由于中下地壳小范围内的物质的不均匀性导致上地壳破裂。     

新疆巴楚-伽师地区上地壳三维速度层析成像

利用近震层析成像方法和2003年新疆巴楚-伽师MS6.8地震走时资料反演得到了震区地下速度图像。结果表明:P波速度在地壳内5km以上表现出了较强的横向非均匀性,反映该区地表的沉积盖层介质特征;在5～22km深度内以NWW和NNE向共轭相交的高速异常带为主,周围速度相对较低。结合构造背景和震源机制解,认为这一区处于NW-SE向的右行走滑和NNE-SSW向的挤压应力双力偶作用下,使得发生的地震有一定的相似性。而NWW和NNE向非均匀性条带为应变能的积累和释放提供了基础,是这次地震发生的一个重要条件。结合宏观调查和石油资料,推断这次地震发生在塔里木盆地西部的一条NWW走向、北倾的巴什托普隐伏断裂上。     

2014年云南鲁甸6.5级地震震源位置及震源区速度结构联合反演

利用震源位置和速度结构的联合反演,得到了2014年云南鲁甸6.5级地震序列的震源位置及震源区速度结构.结果表明,鲁甸地震序列呈共轭分布,余震主要分布在NNE向包谷垴—小河断裂上,另一小部分分布在近EW向的共轭未知断裂上.震源深度剖面结果显示包谷垴—小河断裂是一个走向NNW、高倾角、且倾向为SWW的断裂.震源区地壳结构复杂,存在大面积高速区,地震主要分布在P波速度较高的地区.     

根据接收函数反演得到的首都圈地壳上地幔三维S波速度结构

利用2002~2003年中国地震局地质研究所台阵实验室以唐山大震区为中心布设的40个流动宽频带地震台站和首都圈数字台网的33个宽频带台站的远震数据,采用接收函数非线性反演方法得到其中72个宽频带台站下方60 km深度范围内的S波速度结构.根据得到的各台站下方地壳上地幔的S波速度结构,并综合刘启元等（1997）用接收函数非线性反演方法得到的延怀盆地15个宽频带流动台站下方的地壳上地幔S波速度结构模型,给出了39°N～41°N,114°E~119.5°E区域内沿不同走向、不同深度S波速度分布.由于综合了利用首都圈数字地震台网的宽频带台站以及流动地震台阵的观测数据,本文给出了较前人同类研究空间分辨率更好的结果.结果表明: (1)研究区的速度结构,特别是怀来以东的速度结构十分复杂.在10~20 km深度范围内,研究区地壳具有高速和低速异常块体的交错结构.研究区中上地壳速度结构主要被与张渤地震带大体重合的NW向高速条带和穿越唐山大震区的NE向高速条带所控制,而其中下地壳的速度结构主要为延怀—三河—唐山地区上地幔隆起所控制.(2)研究区内存在若干壳内S波低速体,它们主要分布在唐山,三河及延怀盆地等地区.在这些地区,壳内低速体伴随着壳幔界面的隆起和上地幔顶部速度结构的横向变化.(3)地表断层分布与地壳速度结构分区有较好的相关性,表明断层对不同块体有明显的控制作用.其中,宝坻断裂,香河断裂和唐山断裂均为超壳断裂.(4)首都圈内大地震的分布与壳内低速体及上地幔顶部的速度结构有密切关系.对于唐山大地震的成因,仅考虑板块作用引起的水平应力场是不够的,有必要充分重视由于上地幔变形引起的地壳垂直变形和上地幔物质侵入造成的热效应.     

滇西地区地壳浅部基底速度细结构的研究

本文论述滇西地区思茅－中甸剖面基底导速度细结构的研究结果。基底层项部Ｐｇ界面深度为０－３．５ｋｍ，而底部Ｐ１＾０界面深度为１１．０－１７．０ｋｍ。基底层速度在金河－洱海断裂以南为５．７０－６．３０ｋｍ／ｓ，断裂以北增至６．３０－６．５０ｋｍ／ｓ，其过渡带位于剑川附近，剖面上断裂附近，除界面深度变化外，Ｐｇ面速度横向变化也较明显。速度等值线较为稀疏的景云桥炮南侧、大仓炮附近与支梯炮南侧地区，估计发生     

利用地震走时层析成像方法确定西昌地区断裂带深部几何形态

断裂深部产状和空间几何关系是研究地壳运动变形、动力作用及其地表响应的基础,也是模拟发震断裂与强震关系的基础。为了研究川西南地区强震活动与安宁河、则木河和金河断裂的关系,对盐源-西昌-雷波高分辨地震折射剖面初至Pg波走时和断层面反射波走时进行模拟,获得了川滇活动地块东边界带安宁河、则木河和金河断裂的深部形态。结果表明:在上地壳内,安宁河断裂和则木河断裂东倾32°~35°,其速度结构为舌状低速带,二者规模较大,延伸到了基底。金河断裂东倾约30°,向下延伸至少5km。     

沧州地区地壳上地幔的远震P波三维速度结构成像

利用架设在沧州地区的20台流动地震台站于2006年12月至2010年7月间记录的271个远震事件,读取的2308个P波到时数据,采用地震层析成像方法反演得到沧州及其邻区(38.0°N~39.0°N,116.5°E~117.5°E)的地壳上地幔P波三维速度结构。层析成像结果表明,沧东断裂两侧的地壳介质的速度分布表现出明显的横向差异,浅层速度分布同地表地质结构分布相一致。沧东断裂西北侧沧县隆起的地壳速度较高,表明其基底抬升;断裂带东南边的黄骅拗陷速度较低,说明基底埋藏较深。本文的远震层析成像研究结果和前人使用重力、电磁和人工地震的探测结果都表明,沧东断裂带两侧的地质构造和地球物理性质有明显的变化,这种构造差异在整个地壳中都有体现。     

Characteristics of Horizontal Crustal Movement in the North China Region in the Last Decade

Based on high-precision data obtained in the past decade from GPS re-measurement in the North China Network, the Crustal Movement Observation Network of China (CMONOC) and GPS measurement along the Shanxi graben zone, the status and evolution of horizontal crustal movement in the North China region are analyzed. The results show that (1) the Yanshan tectonic zone (Zhangjiakou-Bohai Sea zone)is an active one with the largest horizontal strain in the North China region; The largest tendency differential movement of adjacent blocks is seen between the Yanshan block and the North China plain block; about 2mm/a (left lateral) ; (2)The significant horizontal differential movement along the boundaries of the North China region is characterized by right-lateral strike-slip movement at the middle-north segment on its west boundary (composed of Yinchuan and other active tectonic zones) and compressive movement at the south segment; while the Yinshan rift zone located along the west segment on its north boundary is dominated by tensile movement. Other boundaries and zones have no obvious differential movement; (3) On the whole, measurements of each period differ from one another, which might result from the nonlinear movement component as well as from the error effect. In the paper, results of the relative movement and strain in different periods are given for different blocks and boundary zones.