Preliminary analysis on the source properties and seismogenic structure of the 2017 M_s7.0 Jiuzhaigou earthquake

At GMT time 13:19, August 8, 2017, an Ms7.0 earthquake struck the Jiuzhaigou region in Sichuan Province, China,causing severe damages and casualties. To investigate the source properties, seismogenic structures, and seismic hazards, we systematically analyzed the tectonic environment, crustal velocity structure in the source region, source parameters and rupture process, Coulomb failure stress changes, and 3-D features of the rupture plane of the Jiuzhaigou earthquake. Our results indicate the following:(1) The Jiuzhaigou earthquake occurred on an unmarked fault belonging to the transition zone of the east Kunlun fault system and is located northwest of the Huya fault.(2) Both the mainshock and aftershock rupture zones are located in a region where crustal seismic velocity changes dramatically. Southeast to the source region, shear wave velocity at the middle to lower crust is significantly low, but it rapidly increases northeastward and lies close to the background velocity across the rupture fault.(3) The aftershock zone is narrow and distributes along the northwest-southeast trend, and most aftershocks occur within a depth range of 5–20 km.(4) The focal mechanism of the Jiuzhaigou earthquake indicates a left-lateral strike-slip fault, with strike, dip, and rake angles of 152°, 74° and 8°, respectively. The hypocenter depth measures 20 km, whereas the centroid depth is about 6 km. The co-seismic rupture mainly concentrates at depths of 3–13 km, with a moment magnitude(M_w) of 6.5.(5) The co-seismic rupture also strengthens the Coulomb failure stress at the two ends of the rupture fault and the east segment of the Tazang fault. Aftershocks relocation results together with geological surveys indicate that the causative fault is a near vertical fault with notable spatial variations: dip angle varies within 66°–89° from northwest to southeast and the average dip angle measures ~84°. The results of this work are of fundamental importance for further studies on the source characteristics, tectonic environment, and seismic hazard evaluation of the Jiuzhaigou earthquake.     

Detection of Antarctic oscillation signals in Earth’s oblateness variations

Variations of Earth’s oblateness (J ₂) reflect a large scale mass redistribution within the Earth system. The climate effect causing J ₂ interannual variations is still not clear, though previous studies indicated it may be related to EI Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). However, we have a new discovery of the significant Antarctic oscillation (AAO) signals in J ₂ interannual variations, especially on 4–6 year scales based on cross wavelet and wavelet coherence analysis with 95% confidence test during 1979–2012. The results additionally indicate that the close phase relationship between J ₂ and AAO (AAO leading J ₂ variations by 3 ± 2 months in phase) is far superior to that between J ₂ and ENSO/PDO on 4–6 year scales. In this work, we discuss, for the first time, a possible geophysical mechanism of AAO effecting J ₂ variations. The investigations are based on the definition of AAO and its spatial–temporal behavior influencing the large-scale mass movement. Finally, an approximate quantitative estimate of the AAO imprint on J ₂ with an emphasis on the atmospheric contribution is made.     

沿海县市级地面沉降信息管理系统的研究

杭嘉湖地区沿海县市积累了大量丰富的地面沉降观测数据,开发并建立一套地面沉降信息管理系统,有效地管理这些数据,并进一步总结沿海县市的地面沉降变化规律,分析地面沉降机理,对防震减灾、城市规划建设等都具有十分重要的意义。本文首先对系统需求进行了分析,并对系统框架、关键技术进行了研究,在此基础上开发出一套地面沉降信息管理系统,并在杭嘉湖地区多个城市得到了应用和推广。     

海鞘中一种酚类衍生物的分离与结构鉴定

从采自青岛海域的柄海鞘Ｓｔｙｅｌａｃｌａｖａ中分离到一种酚类衍生物。经过ＩＲ,ＭＳ,１ＨＮＭＲ和１３ＣＮＭＲ等波谱数据分析,确定其结构为２,４－二叔丁基苯酚。此化合物为首次从该海域海鞘中得到。     

秦岭造山带核部新元古代碰撞变形及其时代--强变形同碰撞花岗岩与弱变形脉体锆石SHRIMP年龄限定

已有的研究表明,主要形成于显生宙的秦岭造山带发生过新元古代碰撞造山作用,但确切的碰撞时间尚需研究。综合物质组成、S→I→A型花岗岩演化、强烈的变形改造、区域变质作用和地质演化等多方面的证据,进一步论证了秦岭造山带核部以牛角山岩体为代表的片麻状过铝质S型花岗岩体为同碰撞岩体;其中,牛角山岩体可能为同碰撞早期岩体。该岩体的15个锆石SHRIMP测年点给出2 0 6 Pb/ 2 38U加权平均年龄为95 5±13Ma。该年龄可代表陆壳下冲深埋、碰撞增厚的时间。在同一地点侵入于岩体中的弱变形花岗岩脉的锆石SHRIMP年龄为92 9±2 5 Ma,从而证明,该片麻状花岗岩体记录的同碰撞变形主要发生于95 5～92 9Ma。这为确定新元古代同碰撞造山作用及其时代提供了有利证据。该碰撞时间滞后于全球格林威尔碰撞造山的时间(130 0～10 0 0 Ma) ,与华南陆块汇聚时间大致相同。根据花岗岩演化特点推测,该事件可能是华北南缘或扬子地块北缘的一次小陆块汇聚增生。     

承德地震前兆台网数据跟踪分析

简要介绍承德地震前兆台网2014-2017年数据跟踪分析工作,对常见典型干扰事件进行分类统计,分析影响制约承德前兆台网观测数据质量的主要因素,为进一步提高数据分析能力与观测资料质量提供有效的技术参考及应对措施。     

重庆芙蓉洞洞穴沉积物δ13C、δ18O特征及意义

利用重庆芙蓉洞内各种新老沉积物的δ13C、δ18O以及对洞穴内的滴水、池水和洞外泉水的长期观测结果,发现芙蓉洞内的次生沉积物中氧同位素变化整体一致,处于稳定温度下(16℃)的平衡分馏状态。而且洞内滴水和池水的氧同位素也相当一致,反映了外界大气降水中氧同位素的年平均状态。芙蓉洞内各种沉积物中碳同位素变化范围很大,从0‰~-11‰均有分布。由于芙蓉洞内各种滴水以及池水中溶解无机碳(DIC)的δ13C变化约在-8‰~-11‰,显著偏轻于部分洞穴沉积物中的δ13C。通过研究从洞穴滴水到形成次生化学沉积物这个过程中的可能影响洞穴沉积物中碳同位素变化的因素,例如：洞穴温度、滴水高度和速率、CO2脱气、生物作用、矿物同质异相转换等,同时参考芙蓉洞内连续生长达37 ka的FR5石笋的碳同位素记录,发现以上可能的影响因素都不能完全解释芙蓉洞内次生沉积物中碳同位素的异常偏重现象。虽然芙蓉洞内广泛存在文石与方解石共存的次生沉积物,但是综合分析表明这些沉积物的氧同位素处于平衡分馏状态,可以用来进行古气候研究。不过在利用石笋碳同位素解释古环境变化时需要慎重,特别是在讨论由文石或文石—方解石混合构成的次生沉积物时。     

Determination of the Neoproterozoic Shicaogou Syn-collisional Granite in the Eastern Qinling Mountains and Its Geological Implications

The Shicaogou granite has been identified as a magnesian (Fe-number=0.71-0.76), calcic to calc-alkalic (MALI=3.84-5.76) and peraluminous (ASI=1.06-1.13) granite of the syn-collisional S-type, with high SiO2(>71%), A12O3 (>13%) and Na2O+K2O (6.28%-7.33%, equal for NaO2 and K2O). Trace element and REE analyses show that the granite is rich in LILE such as of Rb, Sr, Ba and Th, and poor in HFSE like Yb, Y, Zr and Hf. Its Rb/Sr ratio is greater than 1; the contents of Nb and Ta, and the ratio of Nb/Ta as well as the REE geochemical features (e.g. REE abundance, visible fractionation of LREE and HREE and medium to pronounced negative Eu anomalies) are all similar to those of crust-origin, continent-continent syn-collisional granite. Moreover, the granite exhibits almost the same pattern as that of the typical continent-continent syn-collisional granite on the spider diagram and all samples fall within the syn-collisional granite field.The cathodoluminescence (CL) investigations have revealed that the zircon f     

山西吕梁地区汉高山群火山岩成因及其形成环境

吕梁地区汉高山群火山沉积岩是华北克拉通中部带中部中元古代初期火山沉积记录,其成因及形成环境研究对认识华北克拉通结晶基底固结后地质演化有重要意义.该群火山岩为拉斑玄武系列安山岩,SiO2(54.68％ ～56.19％)略低,有较高的MgO(4.97％～6.16％,Mg#=49.4～53.8)及Cr(165×106～174...     

东秦岭早古生代两条不同构造—岩浆杂岩带的形成构造环境

东秦岭造山带早古生代（５００Ｍａ～４００Ｍａ）分别在北秦岭和南秦岭发育两条构造－岩浆杂岩带。北秦岭带由洋盆消减的火山杂岩和深成侵入杂岩组成,是活动陆缘挤压构造背景的产物;南秦岭带由辉长、辉绿岩体、岩脉,超浅成隐爆的碱基性－超基性火山岩和粗面岩组成,是被动陆缘拉张裂陷环境的产物。它们平行造山带走向分布,南、北对峙,构成时空有序的构造－岩浆杂岩带。其形成的构造机制整体上受旱古生代古秦岭洋盆沿商丹一线的俯冲和消减作用的控制,造成北部俯冲挤压,南部拉张裂陷,同时南部的拉张裂陷也受陆壳之下地幔热柱上涌的影响。