2022年门源MS6.9和2016年门源MS6.4地震序列比较分析

2022年1月8日青海省海北州门源县发生M_S6.9地震,震中距离2016年1月21日门源M_S6.4地震震中约33km,两次门源地震均发生在冷龙岭断裂附近,但在震源机制、主发震断层破裂过程及地震序列余震活动等方面显著不同。针对两次门源地震序列的比较分析,对研究冷龙岭断裂及其附近区域强震序列和余震衰减特征等具有重要研究意义。通过对比分析2022年门源M_S6.9地震和2016年门源M_S6.4地震余震的时空演化特征,发现二者在震源过程和断层破裂尺度上存在明显差异,前者发震断层破裂充分,震后能量释放充分,余震丰富且震级偏高;而后者发震断层未破裂至地表,余震震级水平偏低。综合分析两次门源地震序列表现出来的差异性,认为其可能与地震发震断层的破裂过程密切相关,且同时受到区域构造环境的影响。     

2018年9月4日新疆伽师MS5.5地震序列及发震构造讨论

2018年9月4日新疆伽师发生M_S5.5地震,震中处于塔里木地块西北缘,位于1997~1998年伽师强震群震区内。此次伽师地震前发生了M_S4.7前震,截至9月30日最大余震震级为M_S4.6（M_L5.0）,初步判定为前-主-余型地震序列。序列精定位结果显示,余震沿近NE向展布,主震震源深度与1997~1998年伽师强震主震基本一致,发震断层陡立。本文从区域的构造环境、地震震源机制解和余震分布特征等方面分析认为,地震发生在伽师隐伏断裂东南端部,为1997~1998年伽师强震群震区的一次新的构造活动。序列参数、视应力等计算结果显示,伽师M_S5.5地震的预测最大余震震级与最大余震震级M_S4.6接近,表明序列最大余震已经发生。     

用PTD方法测定2017年精河MS6.6地震序列的深度

2017年8月9日精河发生M_S6.6地震,随后发生一系列余震。本文采用PTD方法和新疆测震台网分析的震相数据,基于新疆“2015地壳速度模型”,计算了该地震序列的震源深度,得到M_S6.6主震震源深度约为14km,M_S≥2.5余震深度为9～18km。所有震相数据来自中国地震台网中心编目数据库。     

2017年8月8日九寨沟MS7.0地震序列分析

2017年8月8日四川九寨沟发生M_S7.0地震,该地震发生在巴颜喀喇块体的东北边界,震中区域构造条件复杂,是巴颜喀喇块体北侧左旋走滑环境向东侧逆冲挤压环境过渡的位置,附近地区历史强震较多。九寨沟地震是一次主-余型地震,余震活动水平较弱,主震发生后短时间内M_L≥4.0余震的“等待时间”存在异常,震后较长时间余震活动恢复到正常状态,序列h值、余震视应力等符合主-余型序列特征。序列b值为0.84,G-R关系推测序列最大余震的震级约为M_L5.4（M_S5.0）,8月9日发生的M_S4.8地震是目前该序列的最强余震。通过与1970年以来附近地区7级左右地震序列的对比认为,九寨沟地震与1976年松潘-平武2次7.2级地震序列在余震空间位置、发震构造和震源机制等方面存在较大差异,因此,不具备发育为震群型序列的条件。九寨沟地震主震视应力为0.36～0.38MPa,属于应力下调模型,序列余震的平均视应力水平接近龙门山断裂带附近中小地震的平均背景水平。     

2011年3月10日云南盈江MS5.8地震的微震匹配定位与发震机理研究

前震序列分析在主震成核过程研究中具有重要意义.为探讨2011年3月10日盈江 M_S5．8地震孕震发震机理,利用微震匹配定位技术(MatchandLocate),以92个 M_S≥2．0的地震事件作为模板事件,对主震区周围5个台站连续地震记录进行前震检测,并结合前震、余震分布特点和主震前、后b 值变化趋势等开展综合分析.结果显示,盈江 M_S5．8地震前震主要集中于大盈江断裂第一分支西侧,余震沿ENE、SSE两个优势方向展布,推测此次盈江 M_S5．8地震的主要动力学成因系印度板块的持续向东挤压致使 ENE向的大盈江断裂和SSE向的隐伏断层构成的共轭断层系统发生破裂导致;主震前、后b 值变化暗示腾冲火山区下方广泛存在的流体在此次地震孕育发生过程中起到重要的诱发和促进作用.     

四川长宁地区地震震源参数的时空分布特征

使用谱比法计算得到四川长宁地区2018年12月至2019年7月期间442个地震的震源参数,并进一步分析了震源参数之间的相互关系及应力降的时空分布特征。研究区的地震活动主要集中在长宁背斜核部和南部建武向斜页岩气开采区。研究结果显示,该地区M_L1.3~4.7地震的应力降位于0.02~7.26MPa范围内,超过90%的地震应力降小于2MPa,应力降总体呈现随震级增大而增大的趋势,但与震源深度的关系并不明显。长宁M_S6.0地震发生之前,震源区地震的应力降总体处于较低水平,主震发生之后,短期内余震的应力降较高,随后快速衰减。这些高应力降地震空间上主要集中在长宁余震区的西北段,也是余震强度较大、发生了几次M_S>5.0强余震的位置。建武向斜页岩气开采区地震的应力降总体略低于长宁背斜地区,但差异并不显著。     

2010年青海玉树MS7.1地震序列ETAS模型参数及其变化特征研究

采用时间序列的“传染型余震序列”（ETAS）模型和最大似然法对2010年4月14日青海玉树M_S7.1地震序列的参数进行了估计。为考察其结果的稳定性,设定不同的截止震级和不同的拟合截止时间分别进行序列参数估算。选用截止震级M_C=M_L1.5对玉树M_S7.1地震序列整体的参数进行拟合,计算获得α=0.948 2,p=1.059 6和b=0.817 3。与中国大陆M>7.0地震序列的平均序列参数相比较表明,玉树M_S7.1地震序列表现为触发次级余震的能力较弱,序列衰减速率较快。研究表明,截止震级M_C对α、k和p值有一定的影响。随截止震级逐渐增大,参数k值逐渐减小,α值总体上有增加的趋势,而对p值的影响较小。在地震序列的早期阶段,ETAS模型参数中的p值和α值在震后14天内随时间的变化幅度较为明显,其后各参数变化相对平稳。     

2017年精河MS6.6地震序列及震源特征初步分析

2017年8月9日新疆博尔塔拉州精河县发生M_S6.6地震,震中44.3°N、82.9°E,震源深度11km,精河地震发生在库松木契克山前断裂附近,基于远震波形记录反演的震源机制为逆冲型,地质调查结果显示主震破裂未出露地表。利用地震精定位研究余震的空间分布,结果显示,余震展布与库松木契克山前断裂的走向基本吻合,且余震主要分布在主震西侧,单侧破裂特征明显,余震的深度集中在5～15km。基于M-t图分析序列的衰减特征发现,截至2017年8月20日,序列中M_L2.0、M_L3.0余震相对丰富,衰减基本正常。G-R关系给出的b值为0.54,外推最大余震震级为M_S5.6,h值为2.17,均显示该序列为主-余型。M_S≥4.0余震的等待时间与发生时间较好地满足双对数线性关系,同样为主-余型地震的特征。断层面上静态滑动量分布相对单一且集中,最大滑动位于沿倾向10km处附近,与地质调查主震断层未出露地表的结果一致,同时也表明主震破裂较充分。基于数字波形资料计算出的余震视应力与震级间很好地符合指数关系,扣除震级变化影响后的序列视应力未出现显著高值,也表明此次破裂的能量释放比较充分。     

青海门源MS6.9地震井水位与水温同震响应特征分析

基于全国地震地下流体台网数据库,分析了2022年1月8日青海海北藏族自治州门源县 M_S6.9地震引起的地下流体井水位、水温同震响应特征。结果表明:本次地震引起的水位同震响应观测井数量远大于水温;水位同震响应开始时间、结束时间均优先于水温,水温同震响应是水位同震响应的次生变化。对比门源2022年1月8日 M_S6.9和2016年1月21日 M_S6.4地震,发现地震能量不同是造成两次地震同震响应差异的主要原因。     

河北及周边地区岩石圈磁场变化及震前异常特征

利用2019年度大华北秋季复测156个测点的流动地磁矢量资料,获得河北及周边地区岩石圈磁场半年变化图,分析归纳河北及周边地区岩石圈磁场的总体变化特征,并研究测区内2019年12月3日河北怀安M_S3.4地震和2019年12月5日河北丰南M_S4.5地震前岩石圈磁场局部变化和异常特征。结果表明：丰南M_S4.5地震发生在H矢量的转向区,总强度F负异常的高值区,D要素负异常的高梯度带和Z值变化的高值区;怀安M_S3.4地震则发生在H矢量幅值弱化且转向区,D要素零值线附近的正值区和Z值变化的低值区。     

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.