华北平原不同生长发育期作物长势对气候因子的响应研究

利用卫星遥感归一化植被指数(NDVI)时间序列数据和站点气象数据,从农作物生长发育过程的角度,分析了1981~2008年华北平原农田在12个生长发育期(冬小麦8个、夏玉米4个)对降水和温度不同的响应特征。研究区农田植被指数对降水响应的滞后性强于对温度的滞后性,其中对降水最为敏感的是前1和前2个生长发育期,对温度最为敏感的是同期和前1个生长发育期。不同种类作物在不同时期对气候因子响应不同:冬小麦发育中后期、夏玉米发育中期,绝大多数站点植被指数与降水呈正相关;冬小麦生长发育前中期植被指数与温度呈显著甚至极显著正相关。冬小麦出苗期温度、返青期温度和返青期降水分别与不同时期植被指数显著相关,出苗期和返青期为研究区农田长势对气候因子响应的敏感期。     

Crack－induced anisotropy in the crust from shear wave splitting observed in Tangshan region，North China

Ｃｒａｃｋ－ｉｎｄｕｃｅｄａｎｉｓｏｔｒｏｐｙｉｎｔｈｅｃｒｕｓｔｆｒｏｍｓｈｅａｒｗａｖｅｓｐｌｉｔｔｉｎｇｏｂｓｅｒｖｅｄｉｎＴａｎｇｓｈａｎｒｅｇｉｏｎ，ＮｏｒｔｈＣｈｉｎａＹｕａｎＧＡＯ（高原）Ｓｉ－ＨｕａＺＨＥＮＧ；（郑斯华）ａｎｄＹｏｎｇ...     

沙漠蝗群对印巴边境植被的影响及其未来可能发展趋势

2020年初非洲东北和印巴边境沙漠蝗群席卷多个国家,大面积农田及自然植被被啃食,是什么气候条件促成了此次沙漠蝗灾?距离中国最近的印巴边境蝗群成为研究以及社会关注的热点,蝗灾对当地植被的影响如何?其发展趋势如何?从气候学上分析,蝗灾历史上是否曾经或者未来是否向印度东边迁飞而进入中国呢?本研究利用长时间序列的卫星遥感数据和气象气候观测数据,对沙漠蝗群可能扩展趋势进行了分析。研究结果表明:(1)由于沙漠蝗群的啃食,2020年1月和2月,在蝗群分布区大面积植被区的归一化植被指数较常年大幅度下降,2月(2月3日数据)的啃食面积较1月明显扩大;(2)发生在2018年5月和10月两次印度洋飓风和2019年12月强热带风暴等几个罕见气旋给非洲和阿拉伯半岛带来的强降水,是本次非洲-西亚蝗灾的形成重要原因;(3)从影响沙漠蝗群起飞的气温和沙漠蝗虫适合的降水条件来看,历史上或未来沙漠蝗群迁徙到印度东边的机会很少,进入中国的可能性非常小。     

位场正则化下延在自然电位概率成像中的应用

通过位场正则化向下延拓方法,弥补自然电位法对于地下全空间信息反映不足的客观缺陷,改进仅通过地表数据成像而导致的深度不灵敏状况。在模型分析中,新方案的成像结果和真实模型非常吻合。对于实测资料解释,新方案的处理结果在横向上符合实测数据的异常反映,同时还能够准确的给出地下半空间的纵向信息。     

Study on shear wave splitting in the aftershock region of the Yao＇an earthquake in 2000

After Ms=6.5 Yao＇an earthquake on January 15, 2000, a large amount of aftershock waveforms were recorded by the Near Source Digital Seismic Network （NSSN） installed by Earthquake Administration of Yunnan Province in the aftershock region. It provides profuse data to systematically analyze the features of Yao＇an earthquake. The crustal anisotropy is realized by shear wave splitting propagating in the upper crust. Based on the accurate aftershock relocations, the shear wave splitting parameters are determined with the cross-correlation method, and the results of different stations and regions are discussed in this paper. These conclusions are obtained as follows： firstly, the average fast directions of aftershock region are controlled by the regional stress field and parallel to the maximum horizontal compressive stress direction; secondly, the average fast directions of disparate stations and regions are different and vary with the structural settings and regional stress fields; finally, delay time value is affected by all sorts of factors, which is affinitive with the shear wave propagating medium, especially.     

Crustal structure of Tushka Region, Abu-Simbel, Egypt, inferred from spectral ratios of P waves of local earthquakes

The crustal structure of North Abu-Simbel area was studied using spectral ratios of short-period P waves. Three-component short period seismograms from the Masmas seismic station of the Egyptian National Seismic Network Stations were used. The Thomson-Haskell matrix formulation was applied for linearly elastic, homogeneous crustal layers. The obtained model suggests that the crust under the study region consists of a thin (0.8 km) superficial top layer with a P-wave velocity of 3.8±0.7 km/s and three distinct layers with a mean P-wave velocity of 6.6 km/s, overlaying the upper mantle with a P-wave velocity of 8.3 km/s (fixed). The results were obtained for 14 different earthquakes. The P-wave velocities of the three layers are: 5.8±0.6 km/s, 6.5±0.4 km/s and 7.2±0.3 km/s. The total depth to the Moho interface is 32±2 km. The crustal velocity model estimated using observations is relatively simple, being characterized by smooth velocity variations through the middle and lower crust and normal crustal thickness. The resultant crustal model is consistent with the model obtained from previous deep seismic soundings along the northern part of Aswan lake zone.     

Study on shear wave splitting in the aftershock region of the Yao'an earthquake in 2000

After Ms=6.5 Yao'an earthquake on January 15, 2000, a large amount of aftershock waveforms were recorded by the Near Source Digital Seismic Network (NSSN) installed by Earthquake Administration of Yunnan Province in the aftershock region. It provides profuse data to systematically analyze the features of Yao'an earthquake. The crustal anisotropy is realized by shear wave splitting propagating in the upper crust. Based on the accurate aftershock relocations, the shear wave splitting parameters are determined with the cross-correlation method, and the results of different stations and regions are discussed in this paper. These conclusions are obtained as follows:firstly, the average fast directions of aftershock region are controlled by the regional stress field and parallel to the maximum horizontal compressive stress direction; secondly, the average fast directions of disparate stations and regions are different and vary with the structural settings and regional stress fields; finally, delay time value is affected by all sorts of factors, which is affinitive with the shear wave propagating medium, especially.     

A correlation study between ozone and volcanic activity

A cross-correlation study for time-lags of ±5 yrs between eleven ground based ozone stations (1957–1985) for = 40°N–75° N and = 30° E-114° W and five volcanic emissivity indices has shown their close connection: significant correlations well above 90% were obtained. Intepretation of these positive/negative correlations () was based on the global wind circulation (aided also by a 2-D, 3-D representation between, , ), and the types of volcanic aerosols leading to heterogeneous chemical reactions with ozone.     

The correlation of microtremors: empirical limits and relations between results in frequency and time domains

The use of the correlation of microtremor records is on its way to develop into a common tool to estimate local shear wave velocity structure. For this reason, the establishment of the conditions for the correct use of this method and its limitations when applied to real data is becoming increasingly important. In addition to the use of frequency domain spatial correlation technique [the Spatial Autocorrelation (SPAC) method], the use of time domain correlation to obtain the Green's function of the medium is rapidly gaining presence. We explore the use of microtremor correlation techniques in the time domain to determine local velocity structure and compare with previous results obtained with the same data using SPAC. Our data come from three experiments carried out in Parkway and Wainuiomata valleys in New Zealand, using broad-band portable stations. Interstation distances range from 5 m to 2.1 km, and our results are useful in the frequency band from 0.1 to 7 Hz. Frequency domain correlation requires an isotropic microtremor field, a condition that need not be satisfied in the time domain. Two station correlations provide useful results due to the temporal stationarity and isotropy, in average, of the microtremor wavefield. This manifests itself in the symmetry of the temporal correlation functions with respect to zero time. Our results show that the local velocity structure and the interstation distance are the key factors conditioning the frequency range where surface wave dispersion can be correctly measured either in frequency or time domains. We confirm that, when the interstation distance becomes much larger than the dominant wavelengths, only the correlation in time domain is useful. All our results indicate that the signal obtained in the correlation of vertical component microtremors is due to the fundamental mode of Rayleigh waves, which appears as the most stable propagation mode, without any indication of body waves.