“翻台法”提高地震定位精度的数学原理

对于震中偏离台网情况下的地震定位，常规方法定位效果较差。“翻台法”有效地提高了其定位精度。从均匀地壳模型的走时方程组出发，分析了“翻台法”定位中方程组系数的变化特点，推导了选取最佳翻转台站的方法，并得出如下结论：（１）“翻台法”增加了原定位方程组的约束方程，翻台数与已知条件和所求参数个数有关，从理论上讲，翻转台数超过独立的约束方程数时对增加定位精度不再有意义；（２）考虑到具体的台网布局和台站资料质量，翻转不同台站对提高地震定位精度所起的作用大小各不相同，因而存在选取最佳翻转台站问题。     

Geological Characteristics and Distribution of Submarine Physiographic Features in the Taiwan Region

The sea floor topography around Taiwan is characterized by the asymmetry of its shallow and flat shelves to the west and markedly deep troughs and basins to the south and east. Tectonics and sedimentation are major controls in forming the submarine physiographic features around Taiwan. Three Pliocene-Quaternary shelves are distributed north and west of Taiwan: East China Sea Shelf (passive margin shelf), the Taiwan Strait Shelf (foreland shelf), and Kaoping Shelf (island shelf) from north to south parallel to the strike of Taiwan orogen. Off northeastern Taiwan major morpho/tectonic features associated with plate subduction include E-W trending Ryukyu Trench, Yaeyama accretionary wedge, forearc basins, the Ryukyu Arcs, and the backarc basin of southern Okinawa Trough. Off eastern Taiwan lies the deep Huatung Basin on the Philippine Sea plate with a relatively flat floor, although several large submarine canyons are eroding and crossing the basin floor. Off southeastern Taiwan, the forearc region of the Luzon Arc has been deformed into five alternating N-S trending ridges and troughs during initial arc-continent collision. Among them, the submarine Hengchun Ridge is the seaward continuation of the Hengchun peninsula in southern Taiwan. Off southwestern Taiwan, the broad Kaoping Slope is the major submarine topographic feature with several noticeable submarine canyons. The Penghu Canyon separates this slope from the South China Sea Slope to the west and merges southwards into the Manila Trench in the northern South China Sea. Although most of sea floors of the Taiwan Strait are shallower than 60 m in water depth, there are three noticeable bathymetric lows and two highs in the Taiwan Strait. There exists a close relationship between hydrography and topography in the Taiwan Strait. The circulation of currents in the Taiwan Strait is strongly influenced by seasonal monsoon and semidiurnal tides. The Penghu Channel-Yunchang Ridge can be considered a modern tidal depositional system. The Taiwan Strait shelf has two phases of development. The early phase of the rift margin has developed during Paleoocene-Miocene and it has evolved to the foreland basin in Pliocene-Quaternary time. The present shelf morphology results mainly from combined effects of foreland subsidence and modern sedimentation overprinting that of the Late Pleistocene glaciation about 15,000 years ago.     

高空急流对一次强沙尘暴过程沙尘传输的影响

使用GRAPES_SDM沙尘暴数值模式,对2011年4月28-30日中国北方强沙尘暴天气进行分析,讨论高空急流在此次过程中对沙尘传输的影响,得出以下结论:（1）GRAPES_SDM沙尘暴模式较好地模拟了此次沙尘暴过程的范围和强沙尘暴中心,整体模拟效果较好;（2）沙尘天气发生时间及移动路径与200 hPa高空急流的加强、移动发展有很好的对应关系;（3）高空强纬向风速的加强能够促使中低层形成垂直环流圈,其下沉支流使高空动量有效下传到近地面,进而在地面形成大风及扬沙和沙尘暴天气,强沙尘暴中心位于此垂直环流圈的下沉支;（4）等熵位涡与高空急流及地面沙尘浓度分布演变有很好的对应关系,等熵位涡位于高空急流北侧,地面沙尘浓度中心位于高空急流出口区、等熵位涡中心西南侧、等值线密集带;高层高值位涡区向下延伸的路径与高空急流北侧纬向风速等值线密集带有非常好的对应关系。本文还通过对高空急流轴线动力、热力结构垂直剖面的分析,探讨了高空急流对大范围沙尘天气影响的可能机制。     

A comparative study of the design spectra defined by Eurocode 8, UBC, IBC and Turkish Earthquake Code on R/C sample buildings

Earthquake codes have been revised and updated depending on the improvements in the representation of ground motions, soils and structures. These revisions have been more frequently seen in recent years. One of the key changes in earthquake codes has been performed on the design spectra. In this paper, the design spectra recommended by Turkish Earthquake Code and three other well known codes (Uniform Building Code, Eurocode 8, and International Building Code) are considered for comparison. The main purpose of this study is to investigate the differences caused by the use of different codes in the dynamic analysis and seismic verification of given types of buildings located at code defined different sites. The differences in expressions and some important points for elastic and inelastic spectra defined by the codes are briefly illustrated in tables and figures. Periods, base shears, lateral displacements and interstory drifts for the analyzed buildings located at code defined ground type are comparatively presented.     

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Comparison of Kuqa foreland basin with Persian Gulf Basin in salt tectonics

Compared Kuqa foreland basin with Persian Gulf Basin in development of salt layers, salt tectonics, and the relation between salt tectonics and hydrocarbon, it is concluded that the salt diapirs are relative to hydrocarbon. Searching salt diapirs and related traps in Kuqa foreland basin is important. The forming mechanism of salt tectonic in Kuqa foreland basin is different from that of Hormuz Series, but similar to that of Lower Fars Series/Gachsaran Formation. Inspired by the role of salt tectonics of Lower Fars Series/Gachsaran Formation in hydrocarbon accumulation, the authors considered that the exploration below salt layer should be enforced, and the traps below salt layer in the southern part of the Kuqa foreland basin would be found where salt layer is thicker. On the contrary, the traps should be found both above and below the salt layer in front of the northern mountain where salt layer is thin. The Triassic and Jurassic source rocks are rich in this area with great exploration prospective.     

山龙峪井水位异常与地震关系初探

云南漾濞2017年3月27日5.1级和2021年5月21日6.4级地震前地震活动性和地下流体观测资料存在一些异常共性特征。地震活动性异常共性特征有以下几个方面：云南M≥5.0地震平静异常;云南M4.0～4.9地震平静异常;云南M≥3.0地震低频次活动转为增强态势;滇西M≥4成条带分布;漾濞4级双震前震。地下流体观测资料水温、水汞、固体二氧化碳和水氡存在中短期异常共性特征,其中保山水汞,下关和洱源固体二氧化碳,下关、龙陵和腾冲水氡存在中短期同步性异常共性特征。     

汶川8.0级地震前后陕西地区地倾斜特征迁移分析

对汶川8.0级地震前后陕西地区地倾斜观测资料的分析发现,汶川地震前陕西地区地倾斜存在沿龙门山断裂带方向由东北向西南震中迁移,震后地倾斜反向迁移,迁移平均速度为3～4 km/天。进一步分析认为,震前陕西地区地倾斜向震源迁移可能对汶川8.0级地震起到了触发作用,而震后地倾斜向远场迁移有可能是诱发陕甘川交界的中强余震的主因。     

基于Sentinel-1A的2021年双湖MW5.7地震同震破裂模型

利用Sentinel-1A SAR数据提取2021年西藏双湖县M_W5.7地震同震形变场及2.5D形变场,反演断层滑动分布模型。计算不同节面解为接收断层产生的库仑应力变化差异确定发震构造,并结合余震分布信息评估未来地震风险性。结果表明,地震震中为34.37°N、87.71°E,震源深度6.51 km,发震断层倾向东、走向33°、倾角50°、平均滑动角-74°,以倾滑为主兼有少量左旋走滑分量,最大滑动量0.26 m。短时间内,震区南部地震风险较小,北部则需要结合更多资料进一步分析。本次地震是在羌塘块体持续向东扩张的背景下,受EW向拉伸作用使得黄水湖正断层发生的一次弥散型变形活动,SN向地堑得到进一步扩张。