鲁甸6.5级地震崩滑地质灾害分布与成因探讨

2014年8月3日的云南鲁甸6.5级地震震源机制解、余震震中分布及震后的地震地质调查表明,发震构造为NW向包谷垴-小河断裂,断层发生左旋错动;震源机制与余震精定位数据表明发震断层倾角较陡。崩塌、滑坡分布在一个长轴为NW向的矩形区域内(15km×12km),基岩崩塌指示地震动主方向自北向南由SE向变为SN向,与震源机制解揭示的主压应力方向NW-SE总体一致。地震诱发的次生地质灾害崩塌、滑坡的平面分布特征可以用2种发震模式来解释:1)总体走向为NW的弧形断层发生左旋走滑错动,由北向南,地震动方向由SE向逐渐转变为近SN向;2)除NW向断层的左旋错动之外,NE向断裂也可能被牵动,发生由NW向SE的逆冲运动。地震是由NE、NW 2组断层共同作用的结果,以NW向断层左旋错动为主、NE向断层逆冲为辅。余震震中主要呈NW向线性展布,同时在震中附近存在NE向分布的地震条带,隐含2组断层同时错动的可能性;而鲁甸6.5级地震震中所在的滇东北永善、昭通地区,区域多个地震的震源机制表明,地震断层多以逆冲运动为主,走滑为辅。     

基于强震和测震数据对鲁甸6.5级地震发震断层方向的研究

2014年8月3日16时30分,云南省昭通市鲁甸县发生M6.5地震,宏观震中位于鲁甸县龙头山镇(27.1°N,103.3°E),深度约12km。发震断层为NW向包谷垴-小河断裂,是NE向昭通-鲁甸断裂系的NW向次级走滑断层。文中利用鲁甸地震50个强震台站观测记录与135个测震台站观测记录,分别进行峰值加速度计算和S波辐射图案匹配,对此次地震发震断层方向进行讨论。结果表明,"NW向"的断层方向更符合强震、测震仪器观测值,同时与地震灾害现场调查结果一致。     

昭通-鲁甸断裂晚第四纪活动及其构造意义

昭通-鲁甸断裂带主要由昭通-鲁甸、洒渔河和龙树3条右阶斜列的断裂组成。总体走向40°~60°,洒渔河和龙树断裂倾向SE,昭通-鲁甸断裂倾向NW,它们共同构成几何结构复杂的逆冲断裂系。野外考察表明:沿断裂表现为平直的断层槽地、定向排列的断层三角面、断层陡坎等地貌;大桥边、北闸镇、光明村等地断错了晚更新世—全新世地层;龙树河Ⅰ级阶地上发育高0.5~2.0m的断层陡坎。表明其最新活动时代为晚更新世—全新世,运动性质以逆冲运动为主兼有右旋走滑分量。此外,在NE向断裂间穿插发育的一些NW向断裂,同样表现出晚第四纪活动特征。在2014年鲁甸M6.5地震震区产生了NE和NW向地裂缝和地形反坎等地表形变,与NE和NW向断裂展布基本一致,反映了断裂的新活动特征。由于块体远程变形响应与能量交换传递,在川滇块体东侧形成了凉山次级活动块体,昭通-鲁甸断裂带位于凉山次级活动块体SE向运动的前缘部位。它独特的地理位置和复杂的断裂几何结构成为凉山次级块体构造变形的主要承载体之一,吸收、调节块体SE向运动应变,并构成了凉山次级活动块体的南部边界。从区域构造部位和运动特征分析,昭通-鲁甸断裂带之于凉山次级块体,正如龙门山断裂带之于巴颜喀拉块体。昭通-鲁甸断裂带在活动块体边界和区域构造格架划分上具有重要的构造意义,同时也是滇东北地区重要的地震构造。     

2014年鲁甸MS6.5地震龙头山镇场地高密度电法勘探

鲁甸MS6.5地震造成大量房屋损毁及人员伤亡,其中龙头山镇房屋损毁最严重、人员伤亡最多。地震后,骡马口场地被选为恢复重建的主要场所。应用高密度电法分别对鲁甸震区龙头山场地、骡马口场地进行了勘探作业,初步认为勘探场区内地质构造复杂,断裂发育,构造展布以北东、北西向为主。龙头山场地地层较为破碎,场地内存在一洪积扇,是造成其上建筑物破坏严重的重要因素;骡马口场地地形开阔、地势平坦,是地震恢复重建的有利场所,场地内存在断裂活动的迹象,建筑选址时应注意避让。同时,认为高密度电法具有高效快捷,资料分析处理相对简单,便于震后断裂构造快速判断和场地快速评估。     

2014年鲁甸MS6.5地震触发滑坡编录及其对一些地震参数的指示

2014年8月3日云南鲁甸MS6.5地震不仅直接造成建筑倒塌,还触发了大量的山体滑坡,一些滑坡掩埋了居民点,造成了严重的人员伤亡与财产损失.基于震后高分辨率TH01-02与SJ9A卫星影像,震前高分辨率GF1卫星影像,采用人工目视解译方法,建立了鲁甸地震滑坡编录图.并基于部分滑坡的野外照片与超高分辨率航片对解译结果进行验证.结果表明,鲁甸地震至少触发了1 024处面积＞100m2的滑坡.这些滑坡分布在一个面积约为250km2的区域内,滑坡覆盖面积为5.19km2,总体积约为2.2×107m3.滑坡分布区内的滑坡点密度约为4.03个·km-2,面密度约为2.04％,滑坡平均剥蚀厚度约为86.7mm.对震中周围不同方位的滑坡数量与面积进行了统计,结果显示,滑坡总体上呈NW-SE方向分布,且大多数滑坡位于震中的SE方向.这表明鲁甸地震发震构造更可能是一条NW向断层,且破裂方向是自NW向SE.这与其他地震、地质、地球物理等方面的证据所表现出来的发震断层性质相吻合.将鲁甸地震滑坡分布面积、滑坡数量、面积、体积与全球其他震例进行对比,结果表明,鲁甸地震滑坡分布区较小,但是大滑坡较多、滑坡体积相对大.这反映了鲁甸地震具有震源浅与地震能量衰减迅速的特点.     

鲁甸6.5级地震发震断层判定及其构造属性讨论

鲁甸6.5级地震是川滇菱形块体南南东向运动在青藏高原东缘与华南地块相互作用边界变形带上发生的一次中等强度地震.尽管野外应急科学考察没有发现明显的地震地表破裂带,但云南昭通防震减灾局局域地震台网记录到的余震条带状分布、震后科学考察获得的地震烈度长轴方位和极震区地震裂缝等显示出发震断层为NW向包谷垴-小河断裂,左旋走滑性质,属大凉山断裂南端部组成部分;库仑应力计算表明,鲁甸地震可对周边活动断层系历史地震空段产生应力加载作用,其地震危险性不容忽视.     

2014年川滇交界东段鲁甸M_S 6.5地震序列重新定位及发震构造分析

为了研究鲁甸M_S 6.5地震的余震空间分布特征和探讨震区深部发震构造,本文利用四川、云南省固定地震台网观测资料和震后流动监测资料,采用双差定位方法对2014年8月3日至11日期间发生的鲁甸M_S 6.5主震及506个M_l≥1.5余震序列进行重新定位,获得了359个事件的重定位结果.研究结果显示:鲁甸主震的震源深度为13.8 km,与震源破裂过程显示的初始破裂深度较为接近,余震序列分布纵剖面还显示出余震主要分布在主震上方,且余震序列呈现出近EW向和NW向的不对称共轭状分布,优势分布方向为NW向的地震序列延展范围约20 km左右,并与昭通—鲁甸断裂相交,近EW向地震序列的延展长度约16 km左右.其中,在垂直NW向密集条带的震源深度剖面上,余震序列呈近于直立的条带状聚集,且余震序列震源深度分布的优势区间为3~15 km,较浅的震源深度说明了地震事件大多发生在脆性上地壳内部.地震重定位结果还表明了发震断层呈现高倾角分布的特征,结合震源机制解和地面地震地质调查及科考成果,综合表明和论证了此次鲁甸MS6.5地震的发震断层与NW向的包谷垴—小河断裂密切相关.     

1850年西昌地震地表破裂带的考察研究

根据实地考察研究结果，1850年西昌地震地表形变带全长约90km。现存的地表破裂形迹有地震断层、地震裂缝、地震沟槽、地堑、地震陷坑、冲沟及山脊位错、崩塌滑坡等。最大左旋水平位错5．7m，垂直位错3．8m，形变带严格沿则木河断裂展布。该次地震的发震构造应为则木河断裂，震级M≥7.5级。     

2012年6月24日宁蒗-盐源MS5.7地震发震构造刍议

2012年6月24日宁蒗-盐源M_S5.7地震,位于丽江-小金河断裂西北30km。区域范围内历史上地震频繁,为滇西北地震多发区。震区断裂构造复杂,主要发育NW向、NE向2组断裂,呈棋盘格式展布。经野外实地考察,震中附近发育NW向永宁断裂和NE向日古鲁-岩瓦断裂2条晚更新世活动断裂。永宁断裂由温泉断层、永宁断层和阿拉凹断层组成。在卫星影像上线性特征清晰,断层地貌明显。断裂对永宁、泸沽湖第四纪盆地具有严格的控制作用,沿线多处发育温泉。前所河的多条支流顺断层发育,八七—海衣角一带、日古鲁东山厝附近,多处河流右旋位错。阿拉凹一带断错T₂阶地上更新统沉积,被错地层最新年龄(TL)为(21.19±1.80)ka,是一条以右旋走滑兼正断性质的晚更新世活动断层。日古鲁—岩瓦断裂对岩瓦、日古鲁、利家咀等古近纪、新近纪盆地和永宁第四纪盆地有着明显的控制作用,断错中更新世和上更新世地层。中挖都—利家咀一带,有多条小溪呈现出同步左旋位错特征。断裂在晚更新世有着明显的活动迹象,以左旋走滑运动为主。据震源机制解结果,此次地震为正断兼右旋走滑型地震,NW向节面产状与永宁断裂基本吻合,地震破裂型式与永宁断裂运动学特征一致。地震烈度长轴方向、Ⅷ度烈度异常点线性分布以及构造地裂缝方向均与永宁断裂走向一致。分析认为,永宁断裂为此次地震的发震构造。此外,1996年丽江7.0级地震、1976年中甸5.5级地震以及本次5.7级地震,均具有明显的正倾滑分量。这些地震多分布在哈巴雪山和玉龙雪山新构造隆起周缘。根据区域地形条件分析,该地区的正断层运动作用很可能与地形巨大反差引起的重力势能有关。     

2013 年洱源MS 5. 5 地震烈度分布及震区活动构造背景研究

2013 年洱源MS5. 5 地震震区地质构造复杂,发育有NW 向和NE 向2 组活动断裂。据野外调查和探槽揭示,震中附近的维西-乔后断裂为晚第四纪活动断裂,其新近活动时代主要在晚更新世晚期,全新世仍有较明显的活动迹象,运动性质以右旋走滑为主兼有正断。此次地震等烈度线呈NNW 向的椭圆形展布,极震区达Ⅶ度,长15km,宽10km,面积约279km2。震源机制解显示:该震源断层为正断兼走滑破裂型,与维西-乔后断裂的运动学特征基本吻合;节面Ⅱ为NW 向,与维西-乔后断裂走向基本一致。结合地震烈度分布、滑坡崩塌体分布和微震分布特征等分析推断,此次地震的发震构造应为维西-乔后断裂。震区地处滇西北横断山脉腹地,巨大的地形高差,强烈的表层岩石风化,是造成此次地震破坏较重的自然地理条件,而居民房屋多为抗震性能差的土木结构和砖木结构等简易建筑,是造成地震灾害加重的构筑物背景。     

SCIENCE CHINA Earth Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya

Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate.