Recurrence-time and frequency-slip statistics of slip events on the creeping section of the San Andreas fault in central California

An important question in seismic hazard assessments is the frequency-size and recurrence interval statistics at a point on a fault. Does a point on a fault obey the same statistics as earthquakes in a region do? This is a difficult question to answer because the number of repetitive earthquakes on a particular fault that have been observed is small. In order to overcome this difficulty we consider slip events on the creeping section of the San Andreas fault in central California. Sequences of up to 100 events are obtained from creepmeter records. We compare the statistical distribution of recurrence times with the Brownian passage-time, lognormal, and Weibull distributions and using goodness-of-fit tests find that the Weibull is the preferred distribution. We also consider the frequency–amplitude distribution of slip events. We find that the data clearly do not obey a Gutenberg–Richter distribution. Instead there is a uniform distribution of event sizes for a large fraction of events.     

Complex upper-mantle deformation beneath the North China Craton: implications for lithospheric thinning

The mechanism of lithospheric thinning of the North China Craton (NCC) remains controversial. To constrain the mechanism, this study investigated the upper-mantle deformation pattern of the craton by measuring shear wave splitting at the cratonic edge. The results, derived from data recorded at 47 stations, reveal a complex pattern of mantle deformation. Inside the eastern craton, the majority of fast direction trends SE–NW parallel to the tectonic extension direction accompanying with the lithospheric thinning. At the cratonic edge, 15 stations with only null splitting results indicate undetectable anisotropy beneath the stations. This may be due to upwelling or chaotic ascension of mantle flow. To the north, off the craton, large delay times and variation of splitting parameter with backazimuth are generated by the combination of lithospheric and asthenospheric anisotropy. Based on comparison of the splitting results and the predicted ones by the compelling models, it is likely that lithospheric delamination dominated the lithospheric thinning at the north edge of the NCC during the Mesozoic to Cenozoic.     

用成像测井资料描述碳酸盐岩储集层——以车古20潜山为例

碳酸盐岩、火成岩等复杂性油气藏具有岩性、孔隙空间结构复杂、非均质性强等特点,单纯用常规测井技术很难对这些油气藏进行准确评价,必须借助于成像测井等新技术资料。成像测井不仅能直观地显示各种裂缝、溶洞等地质特征,而且还能定量计算裂缝的各种参数,以及研究孔隙结构。这里详细介绍了成像测井新技术裂缝识别、储层划分、裂缝参数计算、孔洞频谱分析等方法,并利用这些方法描述了车古20潜山碳酸盐岩储集层的裂缝,以及溶蚀孔洞发育特征,识别出了此潜山的储层,还结合其它资料,得出了该潜山油气藏的储层分布规律。     

保持浅层地震反射信息处理方法的研究

在处理泌阳凹陷北部斜坡外带复杂地震资料的过程中,针对浅层地震资料的特点,在消化吸收以往经验的基础上,研制出一套较为完善的、能适应该地区资料特点的浅层处理技术。该套处理技术主要包括叠前去噪技术、静校正技术、地表一致性处理技术、浅层偏移成像技术。实际地震资料的处理结果表明,应用这种技术能够取得较好的处理效果。     

井中声波方法研究的回顾与展望

回顾了井中声波方法二十五年的成长历程和重要成果。展望了井中声波法在金属矿、油气勘探和开发领域的广阔应用前景。提出了未来井中声波方法发展方向的建议。     

Geodynamics of the Early Precambrian,Part 2: Formation of continental crust and sedimentary basins,specificity of the lithosphere

This part of work is aimed at consideration of problems concerning evolution of geodynamic processes based on characteristic structures of the Early Precambrian and their rocks. Considered in the paper are structures characterizing existence of mature continental crust (sedimentary basins), development of the crust (metamorphic belts and granitoids) and underlying upper mantle (lithospheric keel), and amalgamation of crustal domains (continents, microcontinents, terrains) into supercontinents. Geodynamic phenomena of the Early Precambrian comparable with the Phanerozoic ones are distinguishable, on the one hand, and their changes with time of evolutionary character are detectable, on the other. The latter are satisfactorily explainable by secular lowering of the mantle temperature in general and above the top of mantle plumes.