Relative seismic moment tensor determination for Vrancea intermediate depth earthquakes

The method of relative seismic moment tensor determination proposed byStrelitz (1980) is extended a) from an interactive time domain analysis to an automated frequency domain procedure, and b) from an analysis of subevents of complex deep-focus earthquakes to the study of individual source mechanism of small events recorded at few stations.The method was applied to the recovery of seismic moment tensor components of 95 intermediate depth earthquakes withM _L=2.6–4.9 from the Vrancea region, Romania. The main feature of the obtained fault plane solutions is the horizontality ofP axes and the nonhorizontal orienaation ofT axes (inverse faulting). Those events with high fracture energy per unit area of the fault can be grouped unambiguously into three depth intervals: 102–106 km, 124–135 km and 141–152 km. Moreover, their fault plane solutions are similar to ones of all strong and most moderate events from this region and the last two damaging earthquakes (November 10, 1940 withM _W=7.8 and March 4 1977 withM _W=7.5) occurred within the third and first depth interval, respectively. This suggests a possible correlation at these depths between fresh fracture of rocks and the occurrence of strong earthquakes.     

中国大陆活动地块边界带与强震活动

本文在前人对中国大陆及周边活动地块研究和划分的基础上,系统研究了6个Ⅰ级活动地块区和22个Ⅱ级活动地块之间共26个活动边界带的构造变形与强震活动,包括强震分布与活动边界带的关系,边界带构造活动速率与地震活动水平及强震复发期等的关系. 给出了边界带强震活动水平与构造活动速率之间的线性关系和强震复发期长短与构造活动速率的反向变化关系. 从而进一步揭示了中国大陆活动地块构造及其块体运动特征,以及块体边界带的构造变形对强震的控制作用.     

兰州马衔山-兴隆山活动断裂系的构造变形特征和机制

详细考察获得了兰州马衔山—兴隆山活动断裂系4条断裂的几何细结构、新活动性等定量资料。其中马衔山北缘断裂为一条规模大、活动性强的全新世逆左旋走滑断裂，而马衔山南缘断裂、兴隆山南缘断裂和兴隆山北缘断裂等其它3条断裂均为其伴生的逆断裂，为晚更新世活动断裂。它们在深部均可以归并到马衔山北缘断裂这一主走滑断裂带上，是兰州地区重要的控震断裂，影响和制约着本区的地震活动。     

Test of the Empirical Green's Function Deconvolution on Vrancea (Romania) Subcrustal Earthquakes

Vrancea is one of the few singular seismic regions of the world where intermediate-depth earthquakes are permanently generated (around 10 events/month with M _L > 3) within an extremely confined focal volume. This particularity and the relatively large number of short-period waveforms recorded by the Romanian local network provides us the opportunity to test the performance of the empirical Green's function technique in retrieving the source time function and source directivity of the Vrancea earthquakes. Three earthquakes that occurred on March 11, 1983 (M _L = 5.4), April 12, 1983 (M _L = 5.1) and August 7, 1984 (M _L = 5.1) in the lower part of the subducting lithosphere (h 150 km) were analyzed. A set of 28 adjacent events (3.0 < M _L < 4.4) which occurred between 1981 and 1997 were selected as corresponding empirical Green's functions. To test the confidence of the retrieved source time function, we compare the deconvolved pulses using Green's functions of different sizes and recorded simultaneously by short-period and broad-band instruments. Our tests show that the durations of the source time function is well-constrained and is not affected by the limited frequency range of the short-period instruments, or by the relative difference in the focal mechanism between the main event and Green's event. The apparent duration of the source time function outlines source directivity effects, and when these effects are sufficiently strong, they can identify the real fault plane. Relatively short source duration and correspondingly high stress drop values are in agreement with other previous results emphasizing a specific seismic regime in the lower part of the Vrancea subducting lithosphere.     

某水电站工程活动断裂避让带宽度的研究

拟建的某水电站工程位于亚曼苏活动断裂的下盘,为了了解亚曼苏断裂强变形带宽度的范围,确定断裂的避让宽度,为水电站工程选址提供参考依据,利用地表强形变带宽度测量、大型探槽开挖揭露和高密度电法探测的方法,对断裂的强变形带宽度问题进行了详细的分析研究。结果表明,该断裂下盘的强变形带宽度小于50 m,小于相关规范中100 m的避让距离,建议该水电站工程重要构筑物的避让距离为100 m。     

Kizawa tunnel cracked on 23 October 2004 Mid-Niigata earthquake: An example of earthquake-induced damage to tunnels in active-folding zones

Earthquakes in active-folding zones often trigger long-lasting landform changes. Since an underground structure closely follows the motion of its surrounding soils and rocks even after it was damaged in an intense earthquake, experts in charge of reconstruction have to wait until they are convinced that the soils and rocks have been stabilized. Kizawa tunnel was seriously cracked during the 23 October 2004 Mid-Niigata Earthquake. The upper half of the tunnel's cross-section near the north mouth shifted about 0.5 m sideways. Since a ring-shaped cross-section of a tunnel sustains the surrounding soil pressure, this crack pattern seemed to be serious. The authors collaborated with the Nagaoka Regional Development Bureau, Niigata Prefectural Government, in investigating the causes of the damage and in conducting long-term observation of the soils and rocks. This paper summarizes some findings for rational rehabilitations through the investigations.     

川滇地区活动地块现今地壳形变特征

利用川滇地区1998～2002年间200多GPS点位的多期复测结果, 将川滇地区分为9个次级活动块体, 计算了各个活动块体的欧拉旋转矢量和主要活动断裂的运动速度, 并分析了该地区的应变场特征. 结果表明, 川滇地区的地壳运动速度具有北强南弱、西强东弱、以菱形块体为主顺时针旋转的特征; 菱形块体外各个块体运动速度大幅衰减; 与地质结果的差异表明, 川滇菱形块体的现今地壳运动由北往南逐渐增强; 青藏高原物质的侧东向挤出在滇中块体南部明显下降, 而丽江—小金河断裂带的吸收作用并不明显; 川滇地区以压应变为主,四川石棉和云南新平一带出现的应变集中地区也许具有发生中强地震的可能性.     

Ground-motion prediction equations for the intermediate depth Vrancea (Romania) earthquakes

We present the regional ground-motion prediction equations for peak ground acceleration (PGA), peak ground velocity (PGV), pseudo-spectral acceleration (PSA), and seismic intensity (MSK scale) for the Vrancea intermediate depth earthquakes (SE-Carpathians) and territory of Romania. The prediction equations were constructed using the stochastic technique on the basis of the regional Fourier amplitude spectrum (FAS) source scaling and attenuation models and the generalised site amplification functions. Values of considered ground motion parameters are given as the functions of earthquake magnitude, depth and epicentral distance. The developed ground-motion models were tested and calibrated using the available data from the large Vrancea earthquakes. We suggest to use the presented equations for the rapid estimation of seismic effect after strong earthquakes (Shakemap generation) and seismic hazard assessment, both deterministic and probabilistic approaches.     

沂沭断裂晋宁期的构造活动及性质

野外地质现象及４０Ａｒ／３９Ａｒ同位素年龄测定结果证明,沂沭断裂中段的北北东向基底韧性剪切带形成于晋宁期（９４１Ｍａ）。晋宁期华北、扬子两板块陆－陆碰撞作用过程中,由于碰撞边界不吻合而导致的碰撞走滑构造,代表沂沭断裂的早期活动。在此基础上,探讨了沂沭基底韧性剪切带与沂沭断裂以及郯庐断裂活动的关系     

青海可可西里地区的活动构造与地震

青海可可西里地区是青藏高原腹地,自有仪器记录以来,共发生Ｍｓ≥６．０级地震８次,是海省中强地震的主要发震场所之一。本文根据对青海可可西里地区活动断裂的野外考察,较为详细地研究了该区五条活动断裂的几何形态、空间分布及动力学特征。对该区地震活动与构造应力场的关系进行了探讨。结果表明：青海可可西里地区的活动断裂为继承性全新世活动断裂,多发育着史前和现代地震破裂形变带,是该区的主要发震断裂。其中乌兰乌拉湖─岗齐曲活动断裂带是现代地震的主要发震断裂,地表出露有１９８８年４月５日唐古拉Ｍｓ＝７．０级地震的破裂形变带,长达９公里。通过对可可西里地区的野外考察,未发现国外报道的１９７３年７月１６日青海可可西里地区火山活动的事实。     

Characteristics of Tectonic Deformation and Mechanisms for the Active Maxianshan-Xinglongshan Fault System in the Lanzhou Area

A detailed investigation permitted us to obtain quantitative data concerning fine geometric structures of 4 faults of the active Maxianshan-Xinglongshan fault system and the latest movement along them. Of them the northern Maxianshan border fault is a large-scale, strongly active Holocene reverse sinistral strike-slip fault, the other 3 faults, the southern Maxianshan border fault and the southern Xinglongshan border and the northern Xinglongshan border faults are the accompanying active late-Pleistocene thrust faults, which are incorporated into the main strike-slip fault, the northern Maxianshan border fault at depth. It is the most important earthquake-controlling fault in the Lanzhou area, the fault influences and constrains the seismic activity in the area.     

首都圈地壳垂直形变与未来强震活动

据首都圈地区精密水准复测资料,分析了近10年来地壳垂直形变状态与特征。结果表明,北京、天津和河北等平原地区,由于过量开采地下水导致了大空间、大量级的地面沉降,从而无法获得这些区域垂直向构造运动信息。在首都圈地区能够获得构造运动信息的区域主要位于该地区的东北端和西区,东北端为唐山—遵化—兴隆以东和以北的区域,西区指太行山以西的区域。东北端区域整体表现为下降,下降速率为2~ 4 mm/a,但“北升南降”的运动格局没有改变。西区为整体隆升,隆升速率最大近10 m m/a,运动的时空分布从具有“南快北慢”特征的总体上升逐步转变为“北升南降”的有升有降。2001年是西区上述运动性质发生变化的分界线,并由此导致了延怀盆地及其附近的区域出现了比较明显的四象限分布的形变图像。尽管从规模和量级上略小于大同地震前孕震体的变形,但两者的运动图像非常相似,所以该区域可能成为未来强震的孕震地区。     

活动断裂带内第四纪松散沉积物的变形类型

选择了一些典型活断层地质剖面 ,对经受了构造变动的第四纪松散沉积物进行了定向原状样品采集。通过室内样品固结、显微薄片制作和显微构造现象观察 ,从显微域里找到了第四纪松散沉积物变形的一些特点 ,并进行了分类。第四纪松散沉积物的变形类型有两种 :一种是破裂变形 ,主要表现为平行滑动条带、平直滑动界面、碎屑颗粒的破碎等 ;另一种是流动变形 ,主要表现为 :流动构造、碎砾旋转、粘土矿物的拖曳滑动等     

活动断层、地震灾害与减灾对策问题

本文在对活动断层的定义和相关概念的论述基础上,通过活动断层与地震灾害间空间分布上的相关性分析,以及海原断裂带松山和阿尔金断裂带阿克塞老城西等地点的探槽地质剖面的介纠等,揭示出活动断层近地表永久性地质变形的局部化特征,永久变形带宽度一般小于30m。文章最后介绍了美国加州地震断层划定法案的主要内容和活动断层填图计划作为积极有效减灾的一项公益性对策,指出中国大陆地区应有步骤地开展大比例尺活动断层填图来有效地减轻可能遭遇的地震灾害。     

Tectonic deformation buildup in folded mountain terrains in the October 23, 2004, Mid-Niigata earthquake

The October 23, 2004, Mid-Niigata Earthquake jolted central Japan, causing serious damage in a mountainous region of Pliocene sedimentary rocks. Though aftershocks distribution showed a diffused pattern, it indicated that a blind-thrust fault having a NE–SW strike and inclined towards NW was the most causative. Tectonic deformation caused by this faulting was considered to be one of the causes of flooding that occurred about 8 months after the earthquake. Precise digital elevation models (DEMs) before and after the earthquake were obtained with stereoscopy for aerial photographs and laser imaging detection and ranging technology (LIDAR), respectively, and then compared to detect elevation changes and translations. Lastly, the changes of landforms due to landslides are excluded from the estimated deformations to obtain only the components of tectonic deformations of the ground surface.