东坪金矿Ⅰ号脉深部“尖灭”与“再现”处的红外光谱特征

对东坪金矿１号脉深部系统采样并进行红外光谱光密度测定，得出了金矿化的＂尖灭＂与＂再现＂部位的规律性认识。这种认识被深部钻探结果证实。这种规律性对于勘探工程有实际指导意义。     

The Yenice–Gönen active fault (NW Turkey): Active tectonics and palaeoseismology

The Yenice–Gönen Fault (YGF) is one of the most important active tectonic structures in the Biga peninsula. On March 18, 1953, a destructive earthquake (M_w = 7.2) occurred on the YGF, which is considered to be a part of the southern branch of the North Anatolian Fault Zone (NAFZ). A 70 km-long dextral surface rupture formed during the Yenice–Gönen Earthquake (YGE).In this study, structural and palaeoseismological features of the YGF have been investigated. The YGF surface ruptures have been mapped and three trenches were excavated at Muratlar, Karaköy and Seyvan sites.According to the palaeoseismic interpretation and the results of ¹⁴C AMS dating, Seyvan trench shows that an earthquake of palaeoseismic age ca. 620 AD ruptured a different strand of the 1953 fault, producing rather significant surface rupture displacement, while there are indications that at least two older events occurred during the past millennia. Another set of trenches excavated near Gönen town (Muratlar village) revealed extensive liquefaction not only during the 1953 event, but also during a previous earthquake, dated at 1440 AD. The Karaköy trench shows no indications of recent reactivations.Based on the trenching results, we estimate a recurrence interval of 660 ± 160 years for large morphogenic earthquakes, creating linear surface ruptures. The maximum reported displacement during the 1953 earthquake was 4.2 m. Taking into account the palaeoseismologically determined earthquake recurrence interval and maximum displacement, slip-rate of the YGF has been calculated to be 6.3 mm/a, which is consistent with present-day velocities determined by GPS measurements. According to the geological investigations, cumulative displacement of the YGF is 2.3 km. This palaeoseismological study contributes to model the behaviour of large seismogenic faults in the Biga Peninsula.     

小秦岭西段“太华群”多期构造解析“

以宏观和显微构造特征为依据,论述了太华群自形成以来的构造演化过程,初步建立了太华群的构造演化序列,揭示了太华群内部的面理置换、褶皱叠加、断裂复合等规律,探讨了各变形幕的构造式样以及构造变形环境。在其构造层次的综合分析基础上,将太华群的构造演化历史,划分为4个主要构造变形阶段:Ⅰ.粘-塑性构造变形阶段;Ⅱ.塑性构造变形阶段;Ⅲ.脆-韧性构造变形阶段;Ⅳ.脆性构造变形阶段。     

四川省地震重点监视防御区未来地震潜势的研究

本文通过历史地震及现今地震活动性的分析、活断层分段理论及地震空区理论的应用、地震平均复发间隔及复发条件概率的估算以及多学科专家综合评估方法的引入，对川西鲜水河－安宁河－则木河断裂和滇东小江断裂带（中－北段）上15个不同段落的地震潜势进行了深入的研究。进一步修正并重新圈绘出位于鲜水河－安宁河－则木河断裂带上的四川省地震重点监视防御区，其范围：北起道孚县的葛卡或者松林口一带，南至西昌市，沿鲜水河－安宁河－则木河主干断裂带展布，全长约350千米。按对未来地震震级估计的不同，该区可分成3段。第1段位于葛卡或松林口至康定之间，震级估计为7±1／4级；第2段位于康定与石棉之间，估计的震级是61／2±1／4；第3段位于石棉至西昌之间，震级估计为7－71／2。此外，研究结果还显示了小江断裂带上的新塘湾和寻甸一嵩明两个段落未来15年内强震发生的概率相对较高。     

青藏高原东缘高位崩滑灾害多动力多期次演化特征

青藏高原东缘是全球重要的活动构造区,高原峡谷区斜坡陡峻,高位崩滑灾害多发。采用遥感解译、地面调查、钻孔勘探及测年分析等方法,研究了西藏洛隆察达沟和易贡扎木弄沟两处高位崩滑堆积体的多动力多期次演化特征。研究结果表明：(1)沿陡峻沟道发生的高位崩滑灾害多为复合成因,兼具内动力和外动力作用交替促发特征;(2)洛隆察达沟晚更新世以来的堆积物形成序列可分为4期,分别经历了以冰川作用为主的冰碛物堆积、古地震引发的高位崩滑-碎屑流堆积、气候变暖背景下的冰-岩崩滑堆积及近代重力崩滑堆积;(3)易贡扎木弄沟在过去5500年中,先后发生了8次以上较大规模崩滑堆积,测年结果显示了巨型崩滑事件存在百年数量级的复发周期,由于不同期次巨型崩滑体的成因不同,复发周期可能存在长、中、短的差异;(4)近年来受全球气候变化影响,冰-岩崩滑灾害频现,可能成为高原峡谷区高位远程地质灾害研究的焦点。本文关于高位崩滑灾害多期次演化过程的认识对于高原峡谷区重大地质灾害防灾减灾具有一定启示意义。     

A seismic gap in the eastern margin of the Sea of Japan as inferred from the time-space distribution of past seismicity

Abstract Based on the spatial distribution of the focal areas from previous large earthquakes, a significant seismic gap was found off the coast of the Akita Prefecture at the eastern margin of the Sea of Japan. We forecast that the 75 km segment of plate boundary may be ruptured by a large thrust earthquake with a magnitude of 7.5 in the near future. The time of occurrence is uncertain, but the recurrence interval of large earthquakes in this region suggests that it will be no later than the end of next century. The time sequence of large earthquakes in the eastern margin of the Sea of Japan shows a systematic shortening of the earthquake interval for the past 250 years. This feature is simulated successfully by a simple mechanical model that represents a plate boundary by segmented blocks, each of which is composed of a spring friction slider system. We further propose to revise the conventionally accepted plate boundary between the Eurasian and Okhotsk plates in the eastern margin of the Sea of Japan; the observed data of seismic activity and recent crustal deformation indicate that the southern part of the plate boundary traverses the land region from Niigata to Otari along the Shinanogawa seismic belt. The fault geometries of previous large earthquakes show that the mode of plate convergence in the eastern margin of the Sea of Japan is a collision type rather than a simple eastward subduction as was postulated in early studies.     

Distribution of empirical recurrence intervals for segment-rupturing earthquakes on active faults of the Chinese mainland

IntroductionInassessingtheprobabilitiesoftime-dependentandlong-termseismichazardsforsegmentsofactivefaults,itisnecessarytohavetheprobabilitydensity,f(O,fordescribingtherecurrenceintervaldistributionforsegment-rupturingearthquakes.Fromf(nandthefollowingequation,theconditionalprobability,pc,whichincreaseswiththetime,Te,elapsedsincethelatestearthquake,isabletobecalculated(Nishenko,Buland,1987,WorkingGrouponCaliforniaEarthquakeProbabilities,1995;Wen,1995,1998)fwhereATisthetimeintervalforthefor…     

MOMENT DEFICITS ON THE MAJOR FAULTS AND EARTHQUAKE HAZARD ASSESSMENT IN THE EASTERN HIMALAYAN SYNTAXIS

The Eastern Himalayan Syntaxis(EHS)is a critical region for studying the tectonic evolution of Tibetan plateau, which was affected by the intense seismic activities. We use the theory of moment balance, GPS velocities and historical earthquake records to analyze the moment deficits in the EHS, assess the future seismicity and further to predict the recurrence interval of the 1950 Chayu M_S8.6 earthquake. We first collected multiple sets of GPS velocity fields and combined them to reduce the systematic bias. Then a micro-blocks model, constrained by GPS velocities, was built by TDEFNODE software to simultaneously invert the fault elastic strain parameters and rigid motion parameters based on the grid research and simulated annealing methods. The long-term slip rates on the faults were further estimated by the differential motions between the neighboring blocks. The results show that the nearly NS dextral strike-slip faults, Naga Fault and Sagaing Fault, slip with the average rates of ~10.6 and ~16.6mm/a, which are consistent with the lateral extrusion in the Tibetan plateau. However, the Main Frontal Thrust shows a distinguished sinistral strike-slip feature(6~10mm/a), possibly caused by the NNE pushing from the Indian plate to the Eurasian plate. On the other hand, because the EHS is located in frontal area of the collision between Indian and Eurasian plate, most faults show thrusting feature. The most obvious one is the Mishimi Fault, slipping with the rate of 23.3mm/a, implying that the convergence rate of the Indo-European plates is largely absorbed by this fault. The moment accumulation rate in the EHS is higher than the average rate in the Tibetan plateau and the total moment accumulation is(1.15±0.03)×10²² N·m in the last 200a. About 59.7% and 21.6% of the moment accumulation rate concentrate on the Main Frontal Thrust and Mishimi Fault. Second, we selected the earthquake records occurring on the upper crust since 1800AD to analyze the moment release in the EHS based on the data from the International Seismological Centre, United States Geological Survey, and catalogue of historical strong earthquakes in China and some other previous studies. In addition, the Global Centroid Moment Tensor Project and linear regression method were adopted to estimate the relationship between body wave magnitude(m_b), surface wave magnitude(M_S), local magnitude(M_L)and the moment(M₀). Then we further estimated the total fault moment release in the EHS, (5.50±2.54)×10²¹N·m, which is significantly lower than the total moment accumulation. About 79.2% of the moment release occurs on the Mishimi Fault, this is because the 1950 M_S8.6 Chayu earthquake is assumed to have ruptured on this fault. Finally, the present-day moment deficits on the faults in the EHS were calculated by the differences between the moment accumulation and release, which represent the possibility to produce earthquakes on the upper crust faults in the future. The largest moment deficit was found on the Main Frontal Thrust near Bhutan, which is able to rupture with M_W8.1+. Similarly, earthquakes with M_W7.5+ and M_W7.3+ have the potentials to occur on the Naga Fault and the Jiali Fault near Tongmai. However, the future earthquake scales may be less than M_W7.1 on the remaining faults. Moderate minor earthquakes are the main activity in the area near the Yarlung Zangbo Suture zone and the southern Sagaing Fault. Although the Chayu M_S8.6 earthquake occurred near the Mishimi Fault and the eastern MFT, the earthquake risk on those two faults cannot be ignored. Meanwhile, no matter which fault produced the Chayu earthquake, its recurrence will likely be 660a to 1 030a.     

Statistical analysis of the largest possible earthquake magnitudes on the Ecuadorian coast for selected return periods

ABSTRACT

In this work, we have studied the largest earthquake magnitudes on the Ecuadorian coast by using the principles of Extreme Value Analysis based on its two approaches: Block Maxima and Peaks-over-Threshold. First, before modelling the recorded earthquakes, the K-means clustering technique was applied to determine a classification according to the level of magnitude of the earthquakes. Then, models based on the Extreme Value theory of earthquake magnitudes were developed for each of the four clusters that were found, and finally, the best-fitted models were those known as Fréchet and Gumbel ones. The zone with the greatest earthquake magnitudes on the Ecuadorian coast is located between the north of the province of Manabí and the south of the province of Esmeraldas, with a return period of 50 years for an earthquake with magnitude greater than 7.7 M_W.     

1303年山西洪洞8级大地震的时间有序性特征

1303年山西洪洞地震是我国历史记录中被确认的第一个8级大地震。引入有序系列和有序组合的含义,对1303年山西洪洞地震和1556年陕西华县地震分别形成的2个有序系列进行了研究,认为2个8级地震的发震时间有一个时间差(τ)。2个τ值之差用△τ来表示。若2个τ值相差不大,则4个地震(有时可以是3个地震)组成一个有序组合。2个有序系列可有7个有序组合。7个有序组合的τ值在100a～450a范围变化,但它们的△τ值仅在10d～2400d范围内变化,表示了2个有序序列之间的密切联系。震例表明,1303年洪洞大地震与其他8级地震之间的间隔的形成机制可能与沙罗周期有关。