Subsidence in the Kathmandu Basin,before and after the 2015 Mw 7.8 Gorkha Earthquake,Nepal Revealed from Small Baseline Subset-DInSAR Analysis

Land subsidence in densely urbanized areas is a global problem that is primarily caused by excessive groundwater withdrawal. The Kathmandu Basin is one such area where subsidence due to groundwater depletion has been a major problem in recent years. Moreover, on 25 April 2015, this basin experienced large crustal movements caused by the Gorkha earthquake (Mw 7.8). Consequently, the effects of earthquake-induced deformation could affect the temporal and spatial nature of anthropogenic subsidence in the basin. However, this effect has not yet been fully studied. In this paper, we applied the SBAS-DInSAR technique to estimate the spatiotemporal displacement of land subsidence in the Kathmandu Basin before and after the Gorkha earthquake, using 16 ALOS-1 Phased Array L-band Synthetic Aperture Radar (PALSAR) images during the pre-seismic period and 26 Sentinel-1 A/B SAR images during the pre- and post-seismic periods. The results showed that the mean subsidence rate in the central part of the basin was about ?8.2 cm/year before the earthquake. The spatial extents of the subsiding areas were well-correlated with the spatial distributions of the compressible clay layers in the basin. We infer from time-series InSAR analysis that subsidence in the Kathmandu basin could be associated with fluvio-lacustrine (clay) deposits and local hydrogeological conditions. However, after the mainshock, the subsidence rate significantly increased to ?15 and ?12 cm/year during early post-seismic (108 days) and post-seismic (2015–2016) period, respectively. Based on a spatial analysis of the subsidence rate map, the entire basin uplifted during the co-seismic period has started to subside and become stable during the early-post-seismic period. This is because of the elastic rebound of co-seismic deformation. However, interestingly, the localized areas show increased subsidence rates during both the early-post- and post-seismic periods. Therefore, we believe that the large co-seismic deformation experienced in this basin might induce the local subsidence to increase in rate, caused by oscillations of the water table level in the clay layer.     

鄂尔多斯盆地南部马莲河流域地下水中锶富集特征及成因分析

马莲河流域地处鄂尔多斯盆地南部黄土高原区,按储水介质和埋藏条件可将地下水分为黄土潜水、基岩潜水和基岩承压水三类,利用2015—2018年流域的295组地下水水化学数据,分析了地下水中锶(Sr²⁺)的质量浓度水平、垂向分布及沿流向分布的特征,并采用因子相关性研究地下水中Sr²⁺的来源和富集成因。结果表明:马莲河流域地下水富锶现象显著,黄土潜水、基岩潜水和基岩承压水中锶的平均质量浓度分别为1.14 mg/l、1.39 mg/l和5.24 mg/l;地下水中锶富集成因主要是含锶矿物天然状态下的水-岩作用,黄土潜水、基岩潜水和基岩承压水三类地下水中Sr²⁺的主要来源分别为碳酸盐岩与铝硅酸盐岩、碳酸盐岩与硫酸盐和碳酸盐矿物的溶滤作用;地下水中Sr²⁺的质量浓度沿流向呈逐渐增大的趋势,在不同区域中随深度变化的趋势不一致。     

气候变化与人类活动对石家庄市藁城区地下水位埋深的影响分析

为了探寻石家庄市藁城区地下水埋深动态变化规律,以藁城区2001—2018年的年降水量、地下水人工开采量等数据为基础,对藁城区地下水位埋深进行研究。首先采用P-Ⅲ型曲线法确定降水序列的丰、平、枯年份,分析不同降水量情况下地下水位埋深变化规律;其次,利用地下水开采潜力系数法和灰色关联度法对人工开采量和地下水位埋深的关系进行研究。结果表明：1）藁城区地下水位埋深在2001—2016年逐渐增大,在2016—2018年趋于减小,2016年为转折点;在空间上藁城区地下水位埋深呈现出北部埋深小、南部埋深大的特征,北部水位埋深较同期南部水位埋深要浅5~10 m。2）降水是驱动藁城区地下水位埋深变化的重要因素,枯水年水位埋深变幅在0.8~1.5 m之间,平水年水位埋深变幅在0.3~1.2 m之间,丰水年水位埋深变幅在0.3~1.1 m之间。主灌期（3—6月）的地下水位埋深增加速率均为cm/d级,非主灌期（7—10月）的地下水位埋深减少速率均为mm/d级。3）人工开采是驱动藁城区地下水位埋深变化的主导因素,其中农业开采量占人工开采量的80%。综上认为,藁城区一直处于严重超采状态,地下水累计超采量每增加1亿m³,地下水位埋深增加0.45 m。     

微生物对地下水中萘的降解特性及动力学研究

针对我国东北某石油烃污染场地地下水中的萘污染,筛选出了Acinetobacter和Pseudomonas菌属的高效萘降解菌群。该菌群对萘的耐受性较高,且具有良好的乳化性,能够自动调节细胞表面疏水性和自聚集性。不同pH值、萘初始浓度、温度和菌接种量对萘降解效率的影响研究表明:最适菌群生长的pH范围为7.08.0;萘降解效率和速率在1.005.00 mg/L范围内与其初始浓度成正比;在1030 ℃温度范围内均表现出较高的萘降解效率。在此基础上,利用Guass、GuassAmp、LogNomal、Poisson和Pulse数学模型对萘的降解过程进行拟合,其降解速率更符合GuassAmp模型。通过将降解动力学模型中的常数与影响因素相关联,推导出了拟合度较高的多因素影响下的萘降解动力学方程。     

Groundwater characteristics and climate and ecological evolution in the Badain Jaran Desert in the southwest Mongolian Plateau

The Badain Jaran Desert is the third largest desert in China, covering an area of 50000 km². It lies in Northwest China, where the arid and rainless natural environment has a great impact on the climate, environment, and human living conditions. Based on the results of 1∶250000 regional hydrogeological surveys and previous researches, this study systematically investigates the circulation characteristics and resource properties of the groundwater as well as the evolution of the climate and ecological environment since the Quaternary in the Badain Jaran Desert by means of geophysical exploration, hydrogeological drilling, hydrogeochemistry, and isotopic tracing. The results are as follows. (1) The groundwater in the Badain Jaran Desert is mainly recharged through the infiltration of local precipitation and has poor renewability. The groundwater recharge in the desert was calculated to be 1.8684×10⁸ m³/a using the water balance method. (2) The Badain Jaran Desert has experienced four humid stages since the Quaternary, namely MIS 13-15, MIS 5, MIS 3, and the Early–Middle Holocene, but the climate in the desert has shown a trend towards aridity overall. The average annual temperature in the Badain Jaran Desert has significantly increased in the past 50 years. In detail, it has increased by about 2.5°C, with a higher rate in the south than in the north. Meanwhile, the precipitation amount has shown high spatial variability and the climate has shown a warming-drying trend in the past 50 years. (3) The lakes in the hinterland of the Badain Jaran Desert continuously shrank during 1973–2015. However, the vegetation communities maintained a highly natural distribution during 2000–2016, with the vegetation cover has increased overall. Accordingly, the Badain Jaran Desert did not show any notable expansion in that period. This study deepens the understanding of groundwater circulation and the climate and ecological evolution in the Badain Jaran Desert. It will provide a scientific basis for the rational exploitation of the groundwater resources and the ecological protection and restoration in the Badain Jaran Desert.© 2021 China Geology Editorial Office.     

谈地下水数学模型在南干渠灌区中的预测与应用

地下水数学模型是用数学方法表述,经过概化地下水系统,在系统分析地下水补、径、排的基础上,对地下水预测分析的一种有效方法.随着南干渠灌区建成后水量的变化,本文通过选用适宜的数学模型,对灌区地下水资源量进行模拟计算,根据模拟计算结果对灌区地下水升幅进行预测,对灌区生态环境的变化做出评价.     

周至井水位气压效率和相关系数在中强地震前的变化特征

计算了2002～2004年周至井水位的气压效率和相关系数,初步分析了其与地震的关系,认为在2002年甘肃玉门5.9级地震、2003年和2004年甘肃岷县5.2、5.0级地震前,该井水位的气压效率和相关系数同时出现了明显的短临前兆异常。     

Determination of residence time and mixing processes of the Ubatuba,Brazil, inner shelf waters using natural Ra isotopes

Coastal waters contain elevated dissolved activities of short-lived radium isotopes, ²²³Ra and ²²⁴Ra, having half-lives of 11.4 and 3.66 days, respectively. The input of these isotopes near the coast must be balanced by decay and mixing into the open ocean, where excess activities are zero. Since the decay rate is known, in the ideal case the mixing rate may be determined from the offshore distribution of these isotopes. This study found that samples collected in June 2000 followed the expected exponential decrease with distance offshore. We assign a dispersion coefficient of 28–39 m² s⁻¹ for this study. During January 2002 and November 2003, there was not a consistent decrease of activity with distance offshore. This is likely due to the ruggedness of the coastline, where many bays and small islands interrupt simple mixing patterns. To estimate exchange rates during 2002 and 2003, we used a model based on the decrease in the ²²⁴Ra/²²³Ra activity ratio (AR) with time for samples isolated from fresh inputs of Ra. This model yielded residence times of 1–2 weeks for samples collected within 20 km of the coast. We used this residence time to calculate the flux of ²²⁸Ra (half-life = 5.7 years) to the study area necessary to maintain the enrichment relative to ocean water. This enrichment is a factor of ten greater than the flux of ²²⁸Ra expected from submarine groundwater discharge (SGD) occurring within 50 m of shore.     

Isotopic,trace element and nutrient characterization of coastal waters from Ubatuba inner shelf area,south-eastern Brazil

Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (δD, δ¹⁸O, ³H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of ²²²Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m⁻³ which were in opposite relationship with observed salinities. Time series measurements of ²²²Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m⁻³), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the ²²²Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase ²²²Rn concentration during lower sea level, and opposite, during high tides where the ²²²Rn activity concentration is smaller. The estimated SGD fluxes varied during 22–26 November between 8 and 40 cm d⁻¹, with an average value of 21 cm d⁻¹ (the unit is cm³/cm² per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity, which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater–seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region.     

泰山北翼岩溶含水介质分布及地下水循环规律研究

为了深入认识济南岩溶泉水及地热水循环过程,本文以泰山北翼碳酸盐岩含水介质空间分布特征为研究出发点,分析其埋藏条件和连续性特征,并利用数理统计、空间插值、Piper三线图、概念模型等方法,结合水动力场、水化学场、水温度场和水年龄场“四场”分析,揭示区域地下水循环规律。结果表明：地表分水岭与齐广断裂、禹王山断裂、聊考断裂等深大断裂控制了泰山北翼地区岩溶含水介质空间展布,大致呈现由南向北埋藏深度逐渐增大的变化趋势,受马山断裂、东坞断裂、文祖断裂等次级断裂影响岩溶含水介质上下盘有不同错动,但东西展布仍具有较好连续性;区域地下水循环过程极其复杂,泰山岩群、寒武纪及奥陶纪各类含水岩组通过排泄 渗漏、断裂垂向径流、水平地下径流等形式发生水流交汇,并在山前局部地区与第四纪松散孔隙水产生水量交换,最终通过泉或人工开采形式排泄。区域地下水流具有统一的“四场”,并且呈现明显的水平与垂向分带特征,大致沿东阿断裂及其延长线—吴家堡—华山—章丘区—淄博磁村一线划分冷泉与地热水的分界线,以600 m、1000 m划分出浅、中、深循环深度分界线;冷泉以浅循环为主,中、深循环为辅,地下水矿化度、温度、年龄偏低,而地热水以中、深循环为主,浅循环为辅,地下水矿化度、温度、年龄偏大。不同含水介质水流具有一定内在关联,构成一个完整的岩溶水系统。