Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes

The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method. Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows: the strike is 38.23°, the dip angle is 82.54°, the slip angle is -156.08°, the fault length is about 80 km, the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 km. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault, southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earthquake and seismic-wave velocity profile in the focal area all verified our study result.     

镇泾油田长8与长6油层组产能影响因素分析

通过岩芯观察描述、铸体薄片鉴定、毛细管压力分析以及扫描电镜等分析测试手段,结合测井解释成果,分析了镇泾油田长6与长8油层组油井产能的差异及其影响因素。结果表明:沉积相带、储层微观特征、裂缝发育程度、封盖条件以及储层伤害等是决定镇泾油田油井产量的关键因素。因此,在镇泾油田长8和长6油层组开发过程中,应根据不同沉积相带及其储层特征的差异,从改进油井施工工艺等方面入手,调整开发方案,改善储层的渗流能力,从而提高油井的产能。     

Active tectonics around the junction of Southwest Japan and Ryukyu arcs: Control by subducting plate geometry and pre‐Quaternary geologic structure

The origin of active faults in the Inner zone of the western part of Southwest Japan was explained by a decrease of the minimum principal stress and reactivation of ancient geologic structures. Although the E–W maximum principal stress in Southwest Japan due to the collision of the Southwest and Northeast Japan arcs along the Itoigawa–Shizuoka Tectonic Line is assumed to decrease westward, the density of active strike‐slip faults increases in the western margin of the Southwest Japan Arc (western Chugoku and northern Kyushu) where the subducting Philippine Sea Plate dips steeply. The E–W maximum compressional stress is predominant throughout Southwest Japan, while the N–S minimum principal stress that is presumably caused by coupling between Southwest Japan arc and Philippine Sea Plate decreases due to the weak plate coupling as the plate inclination increases under the western margin of Southwest Japan. The increase of the fault density in the western margin of the arc is attributed to a decrease of the minimum principal stress and consequent increase of shear stress. Low slip rates of the active faults in this region support the view that the westward increase of fault density is not a response to increasing maximum stress. These faults of onshore and offshore lie in three distinct domains defined on the basis of fault strike. They are defined domains I, II, and III which are composed of active faults striking ENE–WSW, NW–SE, and NE–SW, respectively. Faulting in domains I, II, and III is related to Miocene rift basins, Eocene normal faults, and Mesozoic strike‐slip faults, respectively. Although these active faults are strike‐slip faults due to E–W maximum stress, it is unclear whether their fault planes are the same as those of pre‐Quaternary dip‐slip faults.     

Variations in stress and driving pore fluid pressure ratio using vein orientations along megasplay faults : Example from the Nobeoka Thrust,Southwest Japan

The Nobeoka Thrust of Southwest Japan is an on‐land example of an ancient megasplay fault that provides an excellent record of deformation and fluid flow at seismogenic depths. The present study reports: (i) temporal stress changes for the seismogenic period of the Nobeoka Thrust; and (ii) spatial heterogeneities in driving pressure ratios P* obtained from mineral veins around the Nobeoka Thrust fault zone. Many quartz veins that filled mode I cracks can be observed in the hanging wall and footwall of the thrust. Inversion for stress orientation suggests that normal faulting dominated in both the hanging wall and footwall, with similar stress axis orientations in both. The orientation of σ₃ for the estimated stress regime is parallel to the slip direction of the Nobeoka Thrust. The detected normal‐faulting‐type stress regimes likely resulted from post‐seismic stress buildup after megathrust earthquakes. The hanging wall of the Nobeoka Thrust has smaller P* values than the footwall. Two possible explanations are proposed for the observed spatial variations in the driving pore fluid pressure ratio, P*: spatial variations in pore fluid pressure P_f are directly responsible for P* variations, or P* variations are controlled by differences in mechanical properties between the hanging wall and footwall.     

鄂尔多斯盆地东部盒8段致密砂岩储层特征——以子洲气田清涧地区为例

清涧地区位于鄂尔多斯盆地东部,是子洲气田稳产的主力接替区块。研究区面积大,钻井数目少,地质认识程度低,尚处于开发评价阶段。以盒8段为研究对象,开展了沉积、储层等精细地质研究工作,并与苏里格致密砂岩气田进行综合对比,落实了有效砂体的厚度、规模、发育频率,总结了有效砂体在空间的分布规律,认识到区内有效砂体分布零星,连续性差,与心滩等优势相带对应关系较好,平面上主要集中在研究区的西砂带,垂向上在盒8上2、盒8下2小层相对发育。结合地质与试气资料,以“连续性有效厚度”为主要依据,将储层分成好、中、差、干层等4种类型,优选了富集区,按照开发级次将研究区划分为3类区,建议在一类区、二类区优选直井开发,不建议部署水平井开发。本研究为气田开发方案编制提供了地质依据,同时也可对类似气田的地质工作起到借鉴作用。     

基于多元参照光谱的SAM岩性划分方法

光谱角制图（SAM）是一种光谱匹配方法,通过量化目标地物光谱与已知参照光谱的相似程度来判断目标地物的类型,广泛应用于多光谱遥感岩性识别。目前,岩石单元训练区内像元的均值光谱,往往作为代表该岩石单元的参照光谱来进行光谱角制图,而使用均值光谱作为参照光谱库的方法,并未考虑岩石单元内部固有的光谱差异性,很大程度上影响了SAM分类效果。为了消除SAM岩性划分时岩石单元内部的光谱差异的影响,本文采用了一种多元参照光谱的SAM岩性划分方法。首先,依据研究区已有地质资料和Landsat-8影像特征,选定各类岩石单元训练区;接着进行各岩石单元训练区内部像元的光谱差异性分析,和各训练区之间的样本可分离性分析,分别使用均值参照光谱库的SAM方法和多元参照光谱库的SAM方法对研究区Landsat-8影像进行了岩性划分实验。研究结果表明,多元参照光谱库的SAM岩性分类方法很好地改善了岩石单元内部光谱差异性对均值参照光谱库的SAM岩性分类方法的影响,分类精度显著提高。     

鄂尔多斯盆地合水地区长8储层成岩作用与有利成岩相带

综合运用物性分析、高压压汞、铸体薄片、电镜扫描技术对鄂尔多斯盆地合水地区长8储层的成岩作用及有利成岩相带进行了分析研究。结果表明：研究区长8储层物性较差,孔喉整体细小,岩性以细-中粒长石岩屑砂岩为主,碎屑成分复杂,成分成熟度低,结构成熟度低到中等。压实作用使储集层的原始孔隙空间损失,胶结作用不仅破坏了部分原生孔隙,而且使部分次生溶孔遭到破坏,溶解作用使储层物性得到了改善。依据成岩作用对物性的影响,划分出5种成岩相,优质储层与成岩相的关系密切,绿泥石胶结-长石溶蚀相物性、含油性最好,绿泥石胶结相次之,它们成为储层发育的有利成岩相带。     

Seismic collapse risk of precast industrial buildings with strong connections

A systematic seismic risk study has been performed on some typical precast industrial buildings that consists of assemblages of cantilever columns with high shear‐span ratios connected to an essentially rigid roof system with strong pinned connections. These buildings were designed according to the requirements of Eurocode 8. The numerical models and procedures were modified in order to address the particular characteristics of the analyzed system. They were also verified by pseudo‐dynamic and cyclic tests of full‐scale large buildings. The intensity measure (IM)‐based solution strategy described in the PEER methodology was used to estimate the seismic collapse risk in terms of peak ground acceleration capacity and the probability of exceeding the global collapse limit state. The effect of the uncertainty in the model parameters on the dispersion of collapse capacity was investigated in depth. Reasonable seismic safety (as proposed by the Joint Committee on Structural Safety) was demonstrated for all the regular single‐storey precast industrial buildings addressed in this study. However, if the flexural strength required by EC8 was exactly matched, and the additional strength, which results from minimum longitudinal reinforcement, was disregarded as well as large dispersion in records was considered, the seismic risk might in some cases exceed the acceptable limits. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrical imaging of sliding geometry and fluids associated with a deep seated landslide (La Clapière,France)

This paper deals with the applicability of electrical resistivity tomography (ERT) for the recognition of large landslide structures at depths, which have never previously been imaged accurately. One of the most studied and instrumented deep landslides in Europe is taken as an example: the La Clapière landslide. The first stage of the study consisted of an accurate geological mapping taking into account a morphological analysis of gravitational deformations. This allowed a very fine definition of the landslide structure, that could be compared with three provided ERT profiles performed within the landslide body. Very good correlations were obtained for the determination of sub‐horizontal structures and associated fluid circulations. It confirmed the position of the sliding surface that reached a maximum depth of 100 m. Forward computing was however necessary to determine the influence and then the presence of vertical discontinuities. It supports the use of ERT as an efficient tool for large scale landslide imaging, such as deep seated landslides. Copyright © 2010 John Wiley & Sons, Ltd.