The Behaviour of a Man-Made Island During the Great Hanshin Earthquake,Japan

This paper describes the behaviour of Port Island in Kobe city during and after the Great Hanshin Earthquake of 17 January 1995. The island is near the city centre and was constructed on the soft seabed in Kobe Port. A vertical array of four seismometers and pore water pressure sensors recorded the response of the ground during and after the earthquake. This study shows how the stiffness of the ground dropped and recovered during and after the earthquake.     

小坡度海底土层地震液化诱发滑移分析方法

地震可使海底砂质、粉质土层液化并导致上部土层的滑移。基于有效应力有限元动力分析方法和Newmark刚性滑块理论,提出了一种计算海底小坡度（≤5o）土层地震液化引起侧向滑移的简化方法。该方法将波浪荷载简化为海底恒定的上覆压力和初始孔压,忽略了海水粘性对海底土层地震反应的影响,利用改进的Seed孔压模型进行动力分析和液化判别,用Newmark滑块理论计算了土层侧向滑移。通过算例和对比分析,研究了海水深度和土层坡度对侧向滑移的影响,表明该方法的有效性,可为近海工程场地地震地质灾害评价提供参考数据。     

隐伏断层在强震砂土液化中的作用——以2008年汶川Mw 7.9地震为例

2008年汶川Mw7.9地震的强地面震动在龙门山前地区造成大量的砂土液化、喷砂冒水等地震灾害现象。震后野外调查发现,砂土液化点主要分布于地下水位只有几米深的山前河流的低阶地处,以大面积砾性土液化为特征,约58%的液化点位于距北川断层20~35km的范围内。对喷水高度及喷水过程进行了详细记录,喷水高度与峰值加速度并没有明显的相关性,喷水高度异常点(2m)集中于山前断裂系统近地表投影处。汶川地震中喷水高度异常、砾性土液化的位置与山前断裂系统的吻合性说明,沉积盆地内的地质构造可能在砂土液化强度和与震动相关的地震灾害方面起到促进作用,所以在类似的地质和水文环境中,除主震的断层错动外,应考虑地质构造在地震危险性评估和建筑物抗震设计中的重要作用。     

Arias Intensity Assessment of Liquefaction Test Sites on the East Side of San Francisco Bay Affected by the Loma Prieta,California, Earthquake of 17 October 1989

Uncompacted artificial-fill deposits on the east side of San Francisco Bay suffered severe levels of soil liquefaction during the Loma Prieta earthquake of 17 October 1989. Damaged areas included maritime-port facilities, office buildings, and shoreline transportation arteries, ranging from 65 to 85 km from the north end of the Loma Prieta rupture zone. Typical of all these sites, which represent occurrences of liquefaction-induced damage farthest from the rupture zone, are low cone penetration test and Standard Penetration Test resistances in zones of cohesionless silty and sandy hydraulic fill, and underlying soft cohesive Holocene and Pleistocene sediment that strongly amplified ground motions. Postearthquake investigations at five study sites using standard penetration tests and cone penetration tests provide a basis for evaluation of the Arias intensity-based methodology for assessment of liquefaction susceptibility.     

从苏门答腊-安达曼到日本东北:特大地震及其引发的超级海啸的启示

2004年12月26日苏门答腊-安达曼MW9.1地震及印度洋超级海啸,以及2011年日本东北MW9.0地震及海啸与核泄漏,给人类带来了巨大的灾难。这两次灾难的接连发生充分暴露了迄今我们对于地震发生规律的认识水平还是很低的,启示我们需要继续加强对地震发生的规律性与地震预测预报的研究。在地震危险性评估中,要努力克服经验性方法的局限性,加强地应力测量以确定断层接近破裂的程度,更直接地估计地震危险性;要最大限度地运用地震、大地测量、地质、地貌等所有可资利用的资料,尽快将学术研究成果应用于防灾减灾实践。要重视不同观测资料的整合集成。要加强学科与学科之间的交叉渗透,自然科学与社会科学之间的合作交流,以及科学界与决策者和社会公众的相互沟通。要加强在海域对地震、海啸的多学科、多手段的监测工作,加强地震破裂过程复杂性的理论与应用研究,提高对地震、海啸(包括局地海啸)的监测、预测预报与预警水平。     

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.     

海底缓坡场地地震侧移数值分析方法

地震动使海底倾斜土层软化、液化并产生永久变形和位移。基于有限元理论,提出一种海底缓坡场地地震引起水平侧移的数值计算方法,将波浪荷载简化为恒定压力荷载和初始孔压,采用二维有效应力动力有限元分析方法进行液化分析,同时由模量软化理论得到土层在地震动各时段的模量,通过非线性静力方法计算软化、液化引起的水平侧移。由算例分析了土层坡度、液化层及上覆非液化层厚度、波浪荷载等因素对侧移的影响,通过对比分析表明了该方法的有效性,可为近海工程场地地震地质灾害评价提供参考数据。     

Strong ground motion modelling of causative fault for the 2002 Avaj earthquake, Iran

The suitability of a very fast method for obtaining synthesizing accelerograms has been demonstrated for a hybrid simulation technique of source wavelet and acceleration envelope waveform for the 2002 Avaj earthquake. This method is based on the amplitude modeled white noise and envelope waveform. The estimation of peak acceleration from a preliminary simulated record is based on using modeling parameters of rupture plane instead of empirical relations for peak acceleration. Based on comparison between observed and simulated strong ground motion data, a fair agreement is observed between simulated and observed records up to distances 40 km for peak acceleration and duration. The most important feature of the recorded strong motion is decay up to a distance of 40 km which is due to direct upgoing shear waves. At distance of 50 to 60 km peak acceleration increase, which is due to postcritical reflection from velocity gradient in the lower crust. A flat trend is observed for peak acceleration at distance of 60 to 100 km. The simulation indicates that the rupture is started at depth of 8 km and propagated from northwest to southeast. The causative fault for the 2002 Avaj earthquake shows similar mechanism to the 1962 Buin-Zahra earthquake.     

A simulation of earthquake induced undrained pore pressure changes with bearing on some soil liquefaction observations following the 2001 Bhuj earthquake

The Bhuj earthquake of January 26th, 2001, induced wide spread liquefaction within the Kachch peninsula. It has been pointed out that inundation due to soil liquefaction was short lived in some parts than in others in the affected region. Several geological, seismological and hydrological factors would have cumulatively contributed to these observed changes. We simulate in this article, undrained or short-term change in pore pressure in a poroelastic half space, in response to a simplified model of the Bhuj earthquake source. We find that the regions of relatively shorter lived inundation due to soil liquefaction may fall in the region where pore pressure responsible for soil liquefaction attributable to strong ground shaking was counteracted by pore pressure changes due to undrained poroelastic effect and vice versa.     

Mapping the liquefaction induced soil moisture changes using remote sensing technique: an attempt to map the earthquake induced liquefaction around Bhuj, Gujarat, India

The Bhuj earthquake (Mw = 7.9) occurred in the western part of India on 26th January 2001 and resulted in the loss of 20,000 lives and caused extensive damage to property. Soil liquefaction related ground failures such as lateral spreading caused significant damage to bridges, dams and other civil engineering structures in entire Kachchh peninsula. The Bhuj area is a part of large sedimentary basin filled with Jurassic, Tertiary and Quaternary deposits. This work pertains to mapping the areas that showed sudden increase in soil moisture after the seismic event, using remote sensing technique. Multi-spectral, spatial and temporal data sets from Indian Remote Sensing Satellite are used to derive the Liquefaction Sensitivity Index (LSeI). The basic concept behind LSeI is that the near infrared and shortwave infrared regions of electromagnetic spectrum are highly absorbed by soil moisture. Thus, the LSeI is herein used to identify the areas with increase in soil moisture after the seismic event. The LSeI map of Bhuj is then correlated with field-based observation on Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR), depth to water table, soil density and Liquefaction Severity Index (LSI). The derived LSeI values are in agreement with liquefaction susceptible criteria and observed LSI (R ² = 0.97). The results of the study indicate that the LSeI after calibration with LSI can be used as a quick tool to map the liquefied areas. On the basis of LSeI, LSI, CRR, CSR and saturation, the unconsolidated sediments of the Bhuj area are classified into three susceptibility classes.     

Active right-lateral strike-slip fault zone along the southern margin of the Japan Sea

We describe an active right-lateral strike-slip fault zone along the southern margin of the Japan Sea, named the Southern Japan Sea Fault Zone (SJSFZ). Onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features, whereas the offshore parts are interpreted from single-/multichannel seismic data combined with borehole information. In an effort to evaluate late Quaternary activity along the fault zone, four active segments separated by uplifting structures are identified in this study. The east–northeast-trending SJSFZ constitutes paired arc-parallel strike-slip faults together with the Median Tectonic Line (MTL), both of which have been activated by oblique subduction of the Philippine Sea plate during the Quaternary. They act as the boundaries of three neotectonic stress domains around the eastern margin of the Eurasian plate: the near-trench Outer zone and NW–SE compressive Inner zone of southwest Japan arc, and the southern Japan Sea deformed under E–W compression from south to north.     

Seismogeological effects on rocks during the 12 April 1998 upper So a Territory earthquake (NW Slovenia)

On 12 April 1998, the strongest earthquake (M_L 5.7), with an epicentre in Slovenia, in the last 100 years shook the upper So a Territory (NW Slovenia). Its maximum intensity was between VII and VIII according to the European Macroseismic Scale (EMS-98). Its epicentre is located in the area SE of the town of Bovec in the Krn mountain range (Julian Alps). Apart from substantial material damage to nearby settlements, the earthquake caused considerable changes to the landscape through many rockfalls and landslides. In this paper, we try to assess the effects of this event on the natural surroundings. The presented results are useful to understand the relation between “seismogeological” effects and the intensity scale EMS-98 for this particular event, but might also be a first step towards a future statistically meaningful assessment of the intensity scale on the basis of “seismogeological” effects.     

Deep seismic reflection profiling across the Ou Backbone range, northern Honshu Island, Japan

Knowledge of the crustal structure, especially the geometry of seismogenic faults, is key to understanding active tectonic processes and assessing the size and frequency of future earthquakes. To reveal the relationship between crustal structure and earthquake activity in northern Honshu Island, common midpoint (CMP) deep reflection profiling and earthquake observations by densely deployed seismic stations were carried out across the active reverse faults that bound the Ou Backbone range. The 40-km-long CMP profiles portray a relatively simple fault geometry within the seismogenic layer. The reverse faults merge at a midcrustal detachment just below the base of the seismogenic layer, producing a pop-up structure that forms the Ou Backbone range. The top of the reflective middle to lower crust (4.5 s in travel time (TWT)) nearly coincides with the bottom of seismogenic layer. The P-wave velocity structure and surface geology suggest that the bounding faults are Miocene normal faults that have been reactivated as reverse faults.     

Paleoseismological evidence for non-characteristic behavior of surface rupture associated with the 2004 Mid-Niigata Prefecture earthquake, central Japan

The 2004 Mid-Niigata Prefecture earthquake sequence (mainshock magnitude, M_JMA 6.8), which occurred in an active fold-and-thrust belt in northern central Japan, generated a small thrust surface rupture (< 20 cm of vertical displacement) along a previously unmapped northern extension of the active Muikamachi–Bonchi–Seien fault zone, on the eastern margin of the epicentral region. To better understand past seismic behavior of the rupture, we conducted a paleoseismic trenching study across the 10-cm-high west-side-up surface rupture at the foot of a pre-existing 1.8-m-high east-facing scarp, which probably resulted from past earthquake(s). A well-defined west-dipping thrust fault zone accompanied by drag folding and displacing the upper Pliocene to lower Pleistocene strata and the unconformably overlying upper Pleistocene (?) to Holocene strata was exposed. The principal fault zone is connected directly to the 2004 surface rupture. From the deformational characteristics of the strata and radiocarbon dating, we inferred that two large paleoseismic events occurred during the past 9000 years prior to the 2004 event. These two pre-2004 events have a nearly identical fault slip (at minimum, 1.5 m), which is ≥ 15 times that of the 2004 event (∼ 10 cm). These paleoseismic data, coupled with the geological and geomorphological features, suggest that the 2004 event represented non-characteristic behavior of the fault, which can potentially generate a more destructive earthquake accompanied by meter-scale surface displacement. This study provides insight into the interpretation of past faulting events and increases our understanding of rupture behavior.     

Principal fault zone width and permeability of the active Neodani fault, Nobi fault system, Southwest Japan

The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10⁻²⁰ m². Water permeability as low as 10⁻²⁰ m² is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip.     

Estimation of causative fault parameters of the Rudbar earthquake of June 20, 1990 from near field SH-wave data

We analyze the strong motion accelerograms recorded for the large (M_S=7.7, M_W=7.3, m_b=6.4) Rudbar earthquake of June 20, 1990. The earthquake had a complex source process. We have identified the imprints of rupture of three localized asperities on the major causative fault on the accelerograms. These asperities are interpreted to correspond to (i) the main shock that initiated the rupture process and was located in the domino block between the Kabateh and Zard Goli faults, (ii) a foreshock that occurred about 10 s earlier in the Kabateh fault and (iii) a later shock, on the western end of the Baklor fault, which terminated the bilateral rupture process at the western end. We estimate the strike, dip and slip of these causative sub-event rupture planes using the SH spectral amplitudes, based on a point source representation of sub-events and a non-linear least square formulation for inversion of the amplitude data. The results of our inversion of the near field data are comparable to other studies based on teleseismic data.     

日本MW9.0级地震同震位移场和应力场的有限元模拟

根据同震位移GPS观测数据, 利用有限元法反演了2011年3月11日本MW9.0级地震的断层滑移模式。在此基础上, 计算了日本MW9.0级地震引起的同震位移场和应力场, 给出了位移和应力的分布, 分析了他们的变化规律并与实测结果进行了对比。计算结果表明: 日本MW9.0级地震的静态断层滑移量最大可达25 m。地震引起断层上盘向东位移, 最大位移在震中附近, 可达24.25 m, 日本东北地区向东位移最大可达6 m。震后地表隆起, 隆起幅度可达5.6 m, 隆起的最高点也在震中附近。日本东北地区东海岸附近有一下沉带, 下沉量可达0.8 m。同震地表位移的计算值与GPS测量结果基本一致。地震引起应力变化, 导致震后应力下降。应力变化是不均匀的, 在震中附近约为9.9 MPa, 在深处可达32 MPa, 在日本东北地区地表应力变化小于4.4 MPa。地震引起的应力变化主要是水平应力, 垂直应力基本不变。     

Significant resistivity changes in the fault zone associated with the 1999 Chi-Chi earthquake, west-central Taiwan

The purpose of this paper is to demonstrate the possible influence of an earthquake on the resistivity distribution in a fault zone. We collected resistivity image profiles across a proposed fault trace prior to the 7.3 magnitude 1999 shallow earthquake in the Chi-Chi area of Taiwan. Significant positive resistivity anomalies were observed in the hanging wall after the earthquake. However, there were negligible resistivity changes in the footwall. From an examination of geoelectric phenomena and surface rupture in the fault zone, it is believed that geoelectric anomalies are associated with abrupt displacement along the active Chelungpu fault. This result indicates a potential for resistivity methods to provide a basis for the monitoring of an active fault.     

2018年5月28日中国吉林松原M5.7级地震引起的液化构造*

2018年5月28日,吉林松原市宁江区毛都站镇牙木吐村发生M5.7级地震(45°16'12″N,124°42'35″E),震源深度13 km,震中位于郯庐断裂带西北侧的扶余/松原—肇东断裂带、第二松花江断裂带和扶余北断裂带交汇处。地震诱发震中距3 km范围内普遍的液化和地表裂缝,给当地居民带来严重灾害。可见液化构造以砂火山为主,其次为液化砂堆、液化砂脉和液化砂席等。液化砂火山又可分为有火山口型砂火山、无火山口型砂火山和无砂型(水)火山。地震液化伴生软沉积物变形构造有变形层理、负载构造和火焰构造、滑塌褶皱、碟状构造和包卷层理等。地震诱发液化砂火山形成过程包括液化层内超孔隙流体压力形成、上覆低渗透层破裂和水、砂喷出地表后砂涌3个阶段。液化和流化砂体在上涌过程中会注入低渗透黏土层形成各种形态的砂脉、砂席和多种类型的变形构造。垂向上地震液化结构可划分为底部松散可液化层、下部液化变形层、上部液化变形层和地表砂火山4层结构。液化层埋深2~5 m,液化层厚度2 m。松原M5.7级地震发震机制为NE-SW(35°~215°)方向挤压应力使断层活跃,推测扶余/松原—肇东断裂是主要的发震断层。松原地震液化构造研究为现代地震活动区和灾害易发区预测提供依据,为地震引发的现代软沉积物变形构造研究提供丰富的素材,兼具将今论古意义,为揭示本世纪以来郯庐断裂带北段进入了一个强断裂和地震活跃阶段提供了最新的实际资料。     

荆沙长江公路大桥主桥墩基地震液化研究

本文利用经验判别法和试验－分析法对荆沙长江公路大桥主桥墩基场地的地震液化进行了综合判别。对现在使用的有关地震液化判别“规范”的应用范围进行了拓展，虽然是初次尝试，但作者认为效果良好。