主磁场梯度的空间分布和长期变化特征

根据GUFM1和IGRF11模型,计算1590—2010年主磁场总强度F、水平分量H和磁倾角I三个要素的水平梯度和垂直梯度,分析了它们的空间分布和长期变化特点.结果表明:F和H的垂直梯度与其磁场的空间分布类似,水平方向的梯度以及磁倾角I在3个方向的梯度都与其磁场分布有明显差异.H的3个方向的梯度分布清楚地指示出南磁极的位置.梯度的长期变化表明,北半球磁场梯度漂移缓慢,南半球磁场梯度变化较快.磁倾角的垂直梯度显示,中太平洋负异常周围的正异常在围绕该负异常旋转.近赤道的梯度异常带在60°W附近的转折是由印度洋异常向非洲方向移动所致.     

Magnetic study of metabasic rocks of Gomoh (India)

Summary A magnetic study of metabasic dykes of pre-Cambrian age in Gomoh has been done. 9 magnetic profiles have been taken with Schmidt vertical force variometer. Direction and intensity of NRM have been determined for 25 oriented samples with an astatic magnetometer. Magnetic susceptibility of the samples has been determined. The magnetic profiles have been interpreted by considering both natural remanence and susceptibility of the rock samples. The remanent magnetic directions have two groups, one corresponding to the northern hemisphere and the other to the southern hemisphere. The corresponding latitudes of the place would then be 34°N and 42°S. It is suggested here that metamorphism of the basic rocks of this area took place during two distinct geologic epochs, one when India was in northern hemisphere and the other when in southern hemisphere, presuming that continental drift has taken place.     

GPS与PS-InSAR联网监测的台湾屏东地区三维地表形变场

联合高精度的GPS水平位移观测和高密度的PS-InSAR雷达视线位移测量,实现地表三维形变的精确反演.本文在准确计算卫星轨道方位角基础上,使用GPS观测位移与星载雷达LOS方向形变的投影转换模型,将雷达LOS方向形变转换为垂直方向位移,并基于地面GPS与SAR影像PS目标联合构建形变监测网,采用参数平差算法估计区域地表形变场.以地质构造活动极其活跃的台湾岛及其西南屏东高雄地区为例,联合屏东地区48个GPS监测台站与雷达PS目标,监测该地区从1995-1999年间由于板块构造挤压运动和地下水抽取导致的三维地表形变.结果表明,该地区年均水平位移量为向西30~50 mm/a,高雄沿海地区发生明显的逆时针西偏南的逐渐增大的水平位移;垂直位移为屏东平原南部呈现-10 mm/a~-15 mm/a的地面沉降,而平原北部和高雄地区呈现约+5 mm/a~+10 mm/a的地面抬升.     

GEOMORPHIC FEATURES AND LATE QUATERNARY SLIP RATE OF THE SOUTHERN ZONGWULONG SHAN FAULT

With the continuous collision of the India and Eurasia plate in Cenozoic, the Qilian Shan began to uplift strongly from 12Ma to 10Ma. Nowadays, Qilian Shan is still uplifting and expanding. In the northern part of Qilian Shan, tectonic activity extends to Hexi Corridor Basin, and has affected Alashan area. In the southern part of Qilian Shan, tectonic activity extends to Qaidam Basin, forming a series of thrust faults in the northern margin of Qaidam Basin and a series of fold deformations in the basin. The southern Zongwulong Shan Fault is located in the northeastern margin of Qaidam Basin, it is the boundary thrust fault between the southern margin of Qilian Shan and Qaidam Basin. GPS studies show that the total crustal shortening rate across the Qilian Shan is 5~8mm/a, which absorbs 20% of the convergence rate of the Indian-Eurasian plate. Concerning how the strain is distributed on individual fault in the Qilian Shan, previous studies mainly focused on the northern margin of the Qilian Shan and the Hexi Corridor Basin, while the study on the southern margin of the Qilian Shan was relatively weak. Therefore, the study of late Quaternary activity of southern Zongwulong Shan Fault in southern margin of Qilian Shan is of great significance to understand the strain distribution pattern in Qilian Shan and the propagation of the fault to the interior of Qaidam Basin. At the same time, because of the strong tectonic activity, the northern margin of Qaidam Basin is also a seismic-prone area. Determining the fault slip rate is also helpful to better understand the movement behaviors of faults and seismic risk assessment.Through remote sensing image interpretation and field geological survey, combined with GPS topographic profiling, cosmogenic nuclides and optically stimulated luminescence dating, we carried out a detailed study at Baijingtu site and Xujixiang site on the southern Zongwulong Shan Fault. The results show that the southern Zongwulong Shan Fault is a Holocene reverse fault, which faulted a series of piedmont alluvial fans and formed a series of fault scarps.The 43ka, 20ka and 11ka ages of the alluvial fan surfaces in this area can be well compared with the ages of terraces and alluvial fan surfaces in the northeastern margin of Tibetan Plateau, and its formation is mainly controlled by climatic factors. Based on the vertical dislocations of the alluvial fans in different periods in Baijingtu and Xujixiang areas, the average vertical slip rate of the southern Zongwulong Shan Fault since late Quaternary is(0.41±0.05)mm/a, and the average horizontal shortening rate is 0.47~0.80mm/a, accounting for about 10% of the crustal shortening in Qilian Shan. These results are helpful to further understand the strain distribution model in Qilian Shan and the tectonic deformation mechanism in the northern margin of Qaidam Basin. The deformation mechanism of the northern Qaidam Basin fault zone, which is composed of the southern Zongwulong Shan Fault, is rather complicated, and it is not a simple piggy-back thrusting style. These faults jointly control the tectonic activity characteristics of the northern Qaidam Basin.     

营口潍坊断裂带新生代活动的特征

营潍断裂带以北西向北京 蓬莱断裂带与之交汇的部位为界分南北两段,北段由辫状交织的两条断裂组成;南段为并列的东西两支断裂,但被黄北、莱北和潍北等北东东向断裂横切成4节。断裂带北段早第三纪水平拉张和垂直差异活动强烈,控制了断陷盆地的发育,晚第三纪—第四纪右旋走滑活动显著。南段本身活动甚弱,但黄北等横向断裂早第三纪水平拉张和垂直差异活动强烈,相应形成了黄北等几个断陷盆地;晚第三纪—第四纪横向断裂仍有活动。断裂带活动具明显的分段性,南段是受横向断裂强烈分割、改造而被“废弃”的一段。断裂带新生代活动具由南部和北部统一向中部迁移的特点,北段还有向东侧迁移的趋势。断裂带地震活动微弱,渤海中部斜穿断裂带分布的北东向地震带,可能是黄河口聊城新生地震构造带向海区延伸的部分     

Seasonal and vertical distributional patterns of siphonophores and medusae in the Chiloé Interior Sea,Chile

The horizontal and vertical distribution of jellyfish was assessed in the Chiloé Inland sea, in the northern area of the Chilean Patagonia. A total of 41 species of cnidarians (8 siphonophores, 31 hydromedusae, 2 scyphomedusae) were collected. Eleven jellyfish species were recorded for the first time in the area. Species richness was higher in spring than in winter (37 vs. 25 species, respectively). Species such as Muggiaea atlantica, Solmundella bitentaculata, and Clytia simplex were extremely abundant in spring. The total abundance (408,157 ind 1000 m^?3) was 18 times higher in spring than in winter (22,406 ind 1000 m^?3).The horizontal distribution of the most abundant species (four in winter, five in spring) showed decreasing abundances in the north–south direction in winter and spring. Peak abundances occurred in the northern microbasins (Reloncaví Fjord, Reloncaví and Ancud gulfs), where the water column stability, phytoplankton and zooplankton abundance were higher, compared with the southern microbasins (Corcovado Gulf, Boca del Guafo). During the spring higher jellyfish abundance season, the vertical distribution of the dominant species (except M. atlantica) showed peak values at mid-depth (30–50 m) and in the deepest sampled layer (50–200 m). This vertical distribution pattern reduced seaward transport in the shallowest layer through estuarine circulation and also limited mortality by predation in the more illuminated shallow layers. Thus, jellyfish were able to remain in the interior waters during the season of maximum biological production.     

1999年台湾集集地震震源破裂过程

使用GPS同震位移资料和远场P波记录,研究了1999年台湾集集地震震源破裂过程．根据地质构造和余震分布引入了一个由弯曲断层面构造的三段“铲状”断层模型．在使用静态GPS位移资料反演集集地震的断层破裂滑动分布时,由于集集地震断层北部近地表破裂的复杂性,在位错模型中考虑拉张分量对地表同震位移的贡献,可更好地同时拟合GPS观测资料的水平和垂向分量．而纯剪切位错弹性半空间模型和分层地壳模型都无法同时拟合水平和垂向GPS观测资料．在此基础上,同时使用静力学同震位移资料和远场地震波形记录,反演集集地震的震源破裂过程．结果表明,一种垂直于断层面的“挤压性”(负)拉张分量几乎集中分布于地震断层的浅部和北部转折处,而这一带地表破裂远较没有(负)拉张分量出现的南部断层复杂．“冒起构造”的数字模拟表明,这种在集集地震破裂转折处及北部断裂带广为出现的典型破裂造成的地表位移可以用具有负拉张分量(挤压)的逆冲断层更好地模拟．而这种负拉张分量(挤压)的分布正是地震破裂性质和几何复杂性的综合反映,震源破裂过程也显示北部转折处破裂在空间和时间上的复杂性.高滑区域与余震分布表现为负相关.     

京津水准复测与垂直形变特征

利用京津城际铁路水准测量资料,绘制了京津地区垂直形变图,发现京津城际铁路水准复测结果同样也出现了与首都圈地区同期水准测量相一致的"南升北降"垂直形变异常现象.分析认为应加强首都圈乃至华北地区的形变监测,为判定形变发展趋势提供依据.     

台湾海峡及其邻区现今构造应力场数值模拟

本文将台湾海峡及其邻区划分为多个具有不同弹性参数的等厚区块,并利用基于弹性理论的有限元数值模型,以GPS观测速度和由震源机制解(FMS)得到的主应力轴方向为约束条件,计算了该研究区的现今构造应力场.结果表明:(1)最大主应力轴在台湾海峡中部和台湾岛弧中部大致为NW-SE向,在东北部呈顺时针旋转,而在南部呈逆时针旋转;(2)研究区水平位移场大致以23°N为界,南强北弱,且在北部呈顺时针旋转,南部呈逆时针旋转;(3)东沙-澎湖-北港隆起因强度大于周边盆地区而成为"阻挡带",导致在其南北出现两个反向的构造逃逸区,并且隆起东南区形变特别强烈,而其西北区则相对较弱.     

软流圈物质运动对鄂尔多斯块体周缘断陷盆地运动特征的影响

研究软流圈物质运动及其对断陷盆地运动特征的影响,是揭示软流圈与岩石圈相互作用,认识华北克拉通破坏的深部动力学过程的基础.本文以鄂尔多斯块体周缘断陷盆地为研究对象,利用数值方法模拟了盆地底部软流圈物质的运动,进而分析了软流圈物质运动对周缘断陷盆地运动特征的影响.研究结果表明:(1)软流圈物质水平运动的区域流向为NWW-SEE向,流速基本一致,局部略有变化.随着深度增加,局部变化特征不再显著;(2)软流圈物质垂向运动存在区域性差异,其中鄂尔多斯体块体北部、西部以及北缘、西缘底部,物质以下沉流为主,尤其西缘下沉流更显著;块体中部、东部以及南缘、西南缘底部,以上升流为主;东缘底部,上升流与下沉流相间分布,以上升流为主.随着深度增加,上述区域性差异特征依然明显;(3)依据热物质的水平拖曳和垂向拉张作用对断陷盆地可能产生的影响,进一步推测,软流圈物质运动有利于北缘盆地的剪切走滑,东缘盆地的伸展拉张,南缘盆地的走滑兼拉张,西缘和西南缘盆地的走滑.     

Paleomagnetic constraints on the Plio–Pleistocene geodynamic evolution of the external central–northern Apennines (Italy)

We report on new paleomagnetic results obtained from 27 sites sampled in the Plio–Pleistocene sequences at the external front of the central–northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated that the present shape of the northern Apenninic arc is due to the oroclinal bending of an originally straight belt oriented around N320° and that vertical axis rotations accompanied the migration of the thrust fronts toward the Adriatic foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153–3166]. We tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the Pliocene and the Pleistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotation is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the ‘Acquasanta’ domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153–3166]. A local significant CCW rotation (23°±10°) is identified in the Early Pleistocene sediments that crop out along the Adriatic coast between Ascoli and Pescara, indicating differential motion of the thrust sheets. This rotation must be younger than 1.43 Ma.     

利用GNSS资料研究新源-和静MS6.6地震前后地壳形变与地震关系

利用2009-2011年三期GNSS观测资料,获得新源—和静6.6级地震前后震中附近区域水平运动速率、主应变率、面膨胀率及最大剪应变率,分析得出:(1)研究区整体呈挤压缩短趋势,南部区域运动速率总体高于北部,而中部区域运动速率高于东西两侧,这与区域构造特点有关。新源—和静MS6.6地震之后,研究区西北部区域的应力场能量得到较大的吸收和释放。(2)从研究区应变分析中可以看出,沿断层出现的主应变率正负交替区域与地震的发生有一定关系。从面膨胀等值线图可以看出,两个面收缩区之间区域是地震发生的重要区域。剪应变区域变化可以反映出地震的破裂方向。     

安宁河-则木河断裂带及周边地区Rayleigh波群速度背景噪声成像研究

安宁河-则木河断裂带位于川滇地块、巴颜喀拉地块和华南地块的交接部位,是川滇菱形块体的东部重要边界。利用布设在安宁河-则木河断裂带周边区域的西昌台阵和川西台阵均历时两年、共187个宽频带地震台站的垂直分量的背景噪声数据,采用噪声层析成像方法获得了这一区域4~20s的Rayleigh波群速度分布图像。与前人研究相比,本文结果的横向分辨率有明显改进,在安宁河-则木河断裂带可达20km左右,在其它区域可以达到20~40km。成像结果表明,安宁河-则木河断裂地区上地壳的速度结构存在明显横向不均匀性,速度分布特征与地表地质构造基本一致,不同周期的速度分布变化较小。盐源盆地、西昌盆地和四川盆地西南缘表现为低速异常。九龙附近和南部的德昌-盐边-巧家附近表现为高速异常,分别与出露的花岗岩体和峨眉山玄武岩有关。在安宁河断裂南段和则木河断裂北段能观测到断裂两侧的速度存在明显差异,其余断裂带两侧的速度对比不明显。贡嘎山附近的中上地壳表现为明显的低速异常,其东侧和西南侧高速体的阻挡,以及鲜水河-安宁河断裂带走向的变化,在贡嘎山区形成一个挤压弯曲段,使得川滇菱形块体的东南向水平运动转换为垂直于断裂的挤压作用和垂直隆升,导致了贡嘎山的快速隆起。     

中国华北地区地磁长期变化的分析

本文分析处理了华北及其邻近地区以及日本三个地磁台1960——1977年的水平分量(H)、垂直分量(Z)和总强度(F)的观测资料。结果表明,华北地区Z的逐年变化在1974————1976年呈现一个由下降到上升的转折,但华北南部和北部的转折时间和速率存在着局部性差异,同时,等变线在空间上亦有由南向北的移动现象。H和F同样具有类似的区域性特征。 华北地区的上述差异,曾被一些作者认为是唐山地震的磁效应。他们提出:北京、昌黎地区地震前出现约数伽马至十几伽马的负异常。从本文的分析可以看出,这种负异常并非局部性的,它只不过是长期变化大尺度区域性特征的一种表现而已。      

川滇菱形块体边界的现今地壳形变

依据川滇菱形块体边界带上所有跨断层测量资料，分析了各场地所处断裂的近期形变特征，结果表明；川滇菱形块体北段形变活动逐渐减弱，南段逐渐加强，各条断裂分别显示出不同的变形特征；菱形块体的现今水平形变以左旋走滑运动为主，垂直形变速度较低，且呈上盘抬升与下降交替出现的运动特征，部分场地的形变异常变化与其邻近的地震活动密切相关。     

The Recent Crustal Deformation on the Sichuan-Yunnan Rhombic Block Boundaries

Based on data from an across-fault survey along the sichuan-Yunnan rhombic block boundaries,the recent deformation characteristics on each fault have been analyzed.It was found that the rate of crustal deformation is slowing down along the northern segment and increasing along the southern segment.Each fault has different features of deformation.The horizontal deformation is mainly characterized by left-lateral strike-slip.The rate of vertical deformation is less than that of the horizontal dformation.The faults have the feature of upper wall uplifting alternated with descending.The anomaly changes of crustal deformation at some sites are closely related to the seismicities near the sites.     

Seismic characterization and monitoring of Fucino Basin (Central Italy)

The Fucino basin (Central Italy) is one of the largest intramountain alluvial plain in the Apennines range. It has a tectonic origin related to the presence of important systems of faults located in its northern and eastern edges. Some of these faults are still active and capable of generating strong seismic events. Site effects related to the soft soils filling the basin can be very important. In this paper we show the preliminary results of a seismic network installed in the Fucino area in order to collect information about site amplification effects and geometry of the basin. We analyze ambient seismic vibrations and recordings of about 150 local earthquakes mainly related to the seismic sequence of the April 6th 2009 Mw 6.3 L’Aquila event. Moreover the strongest events of L’Aquila sequence were analyzed at the three permanent strong-motion stations operating in the area. Using standard spectral techniques we investigate the variation of resonance frequencies within the basin. The ground motion recorded in the Fucino plain is mainly characterized by strong energy at low-frequencies (f < 1 Hz) affecting both horizontal and vertical components. This is particularly evident for stations deployed in correspondence of very thick deposits of sedimentary filling, where a significant increase of ground-motion amplitude and duration is likely caused by locally generated surface waves. The amplification at low-frequencies (<1 Hz) on the horizontal components can reach up a factor of 10 in comparison to nearby stiff sites. However, we found evidences of seismic amplification phenomena also for stiff sites surrounding the basin, including stations of the Italian strong motion network. The independent geological information and the shallow shear-velocity profiles available for the basin can be combined with resonance frequencies for deriving representative geological sections to be used as base for future numerical 2D–3D modeling of the basin.     

Spatio-temporal variation and focal mechanism of the Wenchuan MS8.0 earthquake sequence

Based on abundant aftershock sequence data of the Wenchuan M_S8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along Longmenshan central fault zone of NE direction and form a narrow strip with the length of 325 km and the depth between several and 40 km. The depth profile (section of NW direction) vertical to the strike of aftershock zone (NE direction) shows anisomerous wedgy distribution characteristic of aftershock concentrated regions; it is related to the force form of the Longmenshan nappe tectonic belt. The stronger aftershocks could be divided into northern segment and southern segment apparently and the focal depths of strong aftershocks in the 50 km area between northern segment and southern segment are shallower. It seems like 'to be going to rupture' segment. We also study focal mechanisms and segmentation of strong aftershocks. The principal compressive stress azimuth of aftershock area is WNW direction and the faulting types of aftershocks at southern and northern segment have the same proportion. Because aftershocks distribute on different secondary faults, their focal mechanisms present complex local tectonic stress field. The faulting of seven strong earthquakes on the Longmenshan central fault is mainly characterized by thrust with the component of right-lateral strike-slip. Meantime six strong aftershocks on the Longmenshan back-range fault and Qingchuan fault present strike-slip faulting. At last we discuss the complex segmentation rupture mechanism of the Wenchuan earthquake.     

陕西中南部现今断层滑动速率和闭锁深度反演

位于华北板块和扬子板块之间的陕西中南部由渭河盆地、秦岭造山带和汉中盆地构成,其新构造运动主要形式为山脉隆升、盆地断陷,因此以重复水准测量为手段的地壳垂直运动研究尤为重要.基于研究区1970年以来的多期精密水准测量数据,用GPS垂直运动速率约束的动态平差方法获得了区域垂直运动速度场.以此为基础,用倾滑位错模型、网格搜索方法反演了研究区主要断层倾滑速率和闭锁深度,结果显示:秦岭北缘断裂倾滑速率为2.25～4.53 mm·a~(-1),闭锁深度为7.7～10.0 km;华山山前断裂倾滑速率为2.35～2.71 mm·a~(-1);闭锁深度为2.8～5.0 km,反映了该断裂在华县大地震之后,可能还没有完全闭锁,发生大震的应变能积累条件不足;渭河盆地北缘断裂的倾滑动速率为2.0～2.5 mm·a~(-1),闭锁深度仅为3.0 km左右,说明该断裂以蠕滑运动为主;略阳断裂倾滑速率为3.02 mm·a~(-1),闭锁深度6.7 km,是陕南较活动的断裂.     

小江断裂带周边地区三维P波速度结构及其构造意义

作为青藏高原的东南边界,小江断裂带在高原物质的侧向逃逸中发挥着重要的作用.本文利用流动地震台阵及固定台站的走时观测资料,对小江断裂带及周边区域的壳幔三维P波速度结构进行了研究.结果表明,在中上地壳,小江断裂带内部主要为低速异常,其东侧主要为高速异常.在中下地壳,小江断裂带中部为低速异常,北部和南部主要为高速异常,其中北部的高速异常可延伸到地表附近,南部的高速异常可一直延伸到上地幔.我们推测,小江断裂带中部的低速异常与深部热作用有关;北部的高速异常可能是晚古生代地幔柱活动导致大量基性和超基性幔源物质侵入地壳引起的,它的存在对青藏高原物质向南逃逸起到了一定的阻挡作用,可能是导致川滇活动块体北部次级块体快速抬升的重要因素;南部顶界面向北倾斜的高速异常体对川滇活动块体向南滑移起到了进一步的阻挡作用,导致其上覆的中上地壳低速异常区发生较强的变形和强烈的地震活动,同时在上地幔深度范围起到了稳定的作用,使其南部区域的介质受青藏高原物质向南挤出的影响明显减小.