Insights on the small tsunami from January 28, 2020, Caribbean Sea MW7.7 earthquake by numerical simulation and spectral analysis

A major left-lateral strike-slip Mw7.7 earthquake occurred in the vicinity of the Caribbean Sea on January 28, 2020. As a result, a small-scale tsunami was generated. The properties of the seismogenic source were described using observational data gathered for the earthquake and tsunami, as well as information on the regional tectonic setting. The tsunami was simulated with the COMCOT model and Okada’s dislocation model from finite fault solutions for M_W7.7 Caribbean Sea earthquakes published by the United States Geological Survey. The simulation results were compared to tide gauge records to validate whether the seafloor’s vertical displacement generated by the strike-slip fault caused a small-scale tsunami. We conducted a spectral analysis of the tsunami to better understand the characteristics of tsunami records. The tsunami simulation results showed that the co-seismic vertical displacement caused by a strike-slip M_W7.7 earthquake could have contributed to the small-scale tsunami, but the anomalously large high-frequency tsunami waves recorded by the George Town tide gauge 11 min after the earthquake were unrelated to the earthquake-generated tsunami. According to the spectrum analysis, the predominant period of noticeable high-frequency tsunami waves recorded by the George Town tide gauge occurred only two minutes after the earthquake. This indicates that the source of the small-scale tsunami was close to the George Town station and the possible tsunami source was 150 km away from George Town station. These facts suggest that a submarine landslide was caused by the strike-slip earthquake. The comprehensive analysis showed that the small-scale tsunami was not caused solely by co-seismic seafloor deformation from the strike-slip event but that an earthquake-triggered submarine landslide was the primary cause. Therefore, the combined impact of two sources led to the small-scale tsunami.

     

Diagnostic model construction and example analysis of habitat degradation in enclosed bay: III. Sansha Bay habitat restoration strategy

Unbalanced inputs and outputs of material are the root cause of habitat degradation in Sansha Bay,Fujian Province,China. However,the cumulative pollution varies in different geographic locations and natural conditions in the enclosed bay. In this study,hydrodynamic conditions,sediment characteristics,and aquaculture methods were recognized as the underlying causes of spatial heterogeneity in the distribution of nitrogen and phosphorous pollutants,the two major controlling factors of habitat degradation in the bay area. In order to achieve the goal of balancing nutrient inputs and outputs in Sansha Bay,we developed a feasible and practical zone restoration strategy for reasonable adjustment and arrangement of aquaculture species and production scale in accordance with varying hydrodynamic conditions and sediment characteristics in six sub-bay areas(sub-systems). The proposed zone restoration strategy lays a solid foundation for habitat restoration and management in Sansha Bay.     

基于多种高分辨率卫星数据的TRMM降水数据降尺度研究——以内蒙古地区为例

利用内蒙古地区2001~2010年42个站点实测降水数据作为“真值”,采用LOO（Leave-One-Out）交叉验证、多元逐步回归等方法,构建TRMM（Tropical Rainfall Measuring Mission）降水数据与地形及气候等要素之间的多元回归关系,在此基础上,利用回归值+残差值的方法,获得空间分辨率为1 km×1 km的TRMM年降水数据,并对降尺度TRMM数据进行精度检验。研究表明：① TRMM数据可用于区域年降水量估计,且与实测年降水量呈显著线性关系;② 通过建立不同年份、不同空间分辨率TRMM数据与其它遥感数据的多元统计模型,研究发现在中尺度下TRMM与观测年降水数据拟合效果较好,且在空间分辨率为0.50°×0.50°时的拟合效果最好;③ 降尺度分析提高了TRMM数据对研究区降水时空特征的描述能力,确定性系数、标准误差和偏差均有明显改善,表明降尺度算法在将TRMM降水数据空间分辨率提高到1 km×1 km的同时,并能提高降水数据的精度。     

中国年和季节极端降水时空特征 及极值分布函数上尾部性质

基于热带气旋时间、路径、强度数据和中国728个气象站点1951~2014年日降水数据,分析了年和季节极端降水广义极值（GEV）分布函数特征及受热带气旋的影响。通过检查年和各季节极端降水的非一致性,发现具有变异点或显著时间趋势的站点占总站点数的比例较低。仅考虑满足一致性的站点,年和各季节极端降水GEV分布上尾部在全国大部分区域表现出厚尾特征,且不具有上边界。总体来看北方厚尾特征重于南方,秋季和冬季明显高于年和夏季。年极端降水厚尾特征受到不同季节极端降水机制的混合影响。而且,热带气旋对中国沿海区域极端降水有重要影响,往往引发大量级极端降水。东南沿海地区最大10场极端降水由热带气旋引发的比例达到60%以上。因此热带气旋趋向于增加沿海区域年极端降水GEV分布形状参数的大小,并控制着曲线上尾部的形状。     

大兴安岭北段宜里地区早侏罗世二长花岗岩U-Pb年龄、地球化学特征及其构造意义

本文对大兴安岭北段宜里地区二长花岗岩进行了系统的地球化学及锆石U- Pb同位素年代学研究,旨在查明其成岩时代及岩石成因,并探讨其构造意义。宜里地区二长花岗岩中的锆石均呈半自形—自形,振荡生长环带明显,暗示其岩浆成因。锆石LA- ICP- MS U- Pb同位素定年结果显示,宜里地区二长花岗岩形成于175.8~174.5 Ma,为早侏罗世岩浆事件的产物。岩石具有富硅（SiO2=71. 23%~74.52%）、富碱更富钾（Na2O+K2O=6.31%~8.31%,K2O=2.58%~4.78%）、贫镁（MgO=0.43%~1.50%）、贫钙（CaO=0.91%~1.81%）的特征,铝饱和指数（A/CNK=0.97~1.16）,属于准铝质—弱过铝质高钾钙碱性花岗岩。富集Rb、Th、K等大离子亲石元素,相对亏损Nb、Ta等高场强元素和P、Ti等元素,轻重稀土元素分馏较强（La/Yb）N=14.07~50.34,无明显Eu异常（δEu=0.88~1.71）。花岗岩熔体的锆石饱和温度（714~745℃）明显低于A型花岗岩（＞800℃）,显示出高分异I型花岗岩的特征。岩石学及地球化学特征表明,宜里地区二长花岗岩的形成与俯冲形成的上涌热流加热新增生下地壳发生部分熔融有关。结合区域构造演化及构造判别,认为研究区早侏罗世二长花岗岩形成于蒙古—鄂霍茨克大洋板片南向俯冲作用相关的活动大陆边缘环境。     

河南省南召五峰顶方解石矿床地质特征及找矿标志

河南省南召五峰顶方解石矿床产于二郎坪群大庙组第三岩性段的大理岩中,矿体呈似层状。矿区圈定出方解石矿体2个,矿体长2.0~3.2 km,厚11.91~85.22 m,矿石品位w（CaO）=52.20%~56.25%,白度为85.0%~93.9%,矿石类型为浅灰白色厚层状中粗粒大理岩。文章对矿床含矿岩系、矿体与矿石特征、成矿过程和找矿标志等方面进行了分析研究。结果表明：该矿床为区域变质型矿床,大庙组中浅灰白色大理岩为直接找矿标志。该标志对豫西东秦岭造山带寻找同类矿床有借鉴意义。     

2010—2018年中国北方沙质荒漠化变化分析

荒漠化目前已成为威胁全球生态环境的主要问题。我国北方地区风蚀作用强烈,是土地沙质荒漠化问题最为突出的地区。以沙漠、沙地分布较广的北方6省(区)为研究区,利用遥感技术获取2010—2018年研究区沙质荒漠化演化特征,并将气象、地质等因素进行综合分析,探讨毛乌素沙地、科尔沁沙地沙质荒漠化变化原因。遥感解译结果表明: 2018年北方地区沙质荒漠化土地共35.08万km²,其中重度沙质荒漠化面积11.92万km²,中度沙质荒漠化13.54万km²,轻度沙质荒漠化9.62万km²,主要分布于内蒙古自治区和新疆维吾尔自治区; 2010—2018年,北方地区沙质荒漠化土地面积减少0.73万km²,其中,新疆维吾尔自治区沙质荒漠化面积减少0.48万km²,内蒙古自治区减少0.19万km²,同时有2.78万km²沙质荒漠化土地程度减轻。以毛乌素沙地和科尔沁沙地为典型研究区,对比两沙地生态地质条件差异,总结了沙质荒漠化好转、加重的原因。研究认为,毛乌素沙地应降低人类活动干扰的影响,以自然恢复为主; 科尔沁沙地应加强地下水资源管理,优化植被结构,进一步推进退耕还林、退耕还草工作。研究成果为我国北方沙质荒漠化地区生态保护修复提供了科学参考。     

Advances in interscale and interdisciplinary approaches to the South China Sea

The South China Sea (SCS) connects the Pacific Ocean and the Indian Ocean, and acts as an important part in regional and global climate systems (e.g., Qu et al., 2009; Wang et al., 2009). Multi-scale dynamic and biogeochemical processes in the SCS, comprising a hot spot in marginal sea studies, have attracted great attentions from researchers (e.g., Chen et al., 2020; Hu et al., 2020). The South China Sea Annual Meeting (SCSAM) 2021, recently held on October 22–24 in Zhanjiang, China, focused on academic exchanges of the newly research results and progresses in the interdisciplinary multi-scale processes in the SCS. The SCSAM 2021 is the eighth international workshop of the series, which started in April 2013 (Zhu, 2013) and renamed as SCSAM in 2018. There were 90 oral presentations and 57 posters in the meeting this year, which attracted attentions of more than 2000 audiences both on line and on site. This short article summaries the cutting-edge advances in interscale and interdisciplinary approaches to the SCS from the meeting presentations and the associated research.     

2020年7月12日唐山古冶MS 5.1地震震源参数

利用河北及邻区地震台网提供的震相观测报告,使用双差定位方法,对2020年7月12日唐山古冶M_S 5.1地震序列进行重新定位,并基于部分地震台站记录的波形资料,采用近震全波形方法,反演得到主震震源机制解。精定位结果显示,此次地震序列展布长度约8 km,余震自主震位置向SW扩展,震源深度优势分布范围在10—18 km,发震断层面较陡,倾向SE。震源机制解显示,主震为一次走滑型事件,结合序列展布形态和地震活动背景,SW—NE向近似直立节面为可能发震断层面,与1976年唐山M_S 7.8主震断层特征基本一致。综上所述,古冶M_S 5.1地震为唐山M_S 7.8地震的又一次余震,属唐山老震区正常地震活动。