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1.
北京时间2021年5月21日21时48分36秒,云南省大理州漾濞县发生MS 6.4地震。利用云南数字地震台网2021年5月18日至8月22日的震相报告,采用双差地震定位法,对漾濞MS 6.4地震序列进行重新定位。重新定位结果显示序列呈NW向优势分布,破裂长约20 km,宽约7 km,对重新定位结果进行误差分析,水平方向定位误差约为0.8 km,垂直方向定位误差约为1.0 km,定位结果具有较好的稳定性。依据震中分布的走向将序列划分为NW向的主断层与NNW向的分支断层,主断层存在较为明显的分段现象,分支断层呈雁列状分布。根据小震丛集性发生在大震断层面及其附近的原则,利用重新定位后的小震震源位置反演得到漾濞MS 6.4序列主断层走向约320°,倾角约89°,深度范围3~13 km。根据拟合得到的断层在地表的投影位置,推测本次地震的发震断层为维西-乔后断裂西侧的草坪断裂。基于断层滑动量分布识别出3个凹凸体,结合序列时空演化特征,分析了漾濞MS 6.4地震序列的破裂过程,结果显示断层中段的凹凸体发生初始破裂...  相似文献   
2.
本文基于有限断层模型反演方法,利用区域宽频带数据反演了2021年5月云南漾濞MS6.4地震的震源破裂过程,结果显示:此次地震的发震断层走向为SE向,主要以右旋走滑为主.破裂主要发生在震源东南侧,最大错动量约为0.55 m,位于深度约9 km处,发生明显破裂的深度约达13 km.此次地震释放的标量地震矩为1.48×1018N·m,相当于矩震级MW6.05.地震能量主要在前11 s释放.在深度为6~8 km处破裂速度有明显的变快,可能加剧了地表的震动.  相似文献   
3.
张岚  李琦  唐河  孙文科 《地球物理学报》2022,65(3):1044-1056
2021年5月22日,中国青海玛多县发生了MW7.5地震.针对此次地震,国内外多家机构发布的震源机制解和有限断层滑动模型结果大都是基于半无限空间地球模型的位错理论反演得到的,未考虑地球曲率和层状效应的影响.该影响的量级以及其是否可以忽略目前仍是一个未知问题,值得研究.为此,本文利用美国地质调查局(USGS)、中国科学院青藏高原研究所以及中国地震局地球物理研究所提供的三个断层模型,基于弹性半无限空间、均质球、PREM三种地球模型的位错理论,分别计算了地表同震位移场和应变场,并对比分析了这些结果的差异.我们发现基于PREM位错理论的同震位移场与半无限空间模型的对应值差异约为3~28 cm,占PREM位错理论值的10%~30%,应变场差异更大,表明地球曲率和层状效应的影响不可忽略.此外,理论同震形变结果与GNSS和InSAR形变观测数据对比发现,基于PREM模型的理论位移场最接近于观测值.利用InSAR数据和三种地球模型反演得到的有限断层滑动模型存在差异,说明了地球模型的选择对断层模型的反演具有一定影响.本文的结果为今后对此次地震的观测数据物理解释和断层滑动反演提供了理论参考.  相似文献   
4.
The simplified macro‐equations of porous elastic media are presented based on Hickey's theory upon ignoring effects of thermomechanical coupling and fluctuations of porosity and density induced by passing waves. The macro‐equations with definite physical parameters predict two types of compressional waves (P wave) and two types of shear waves (S wave). The first types of P and S waves, similar to the fast P wave and S wave in Biot's theory, propagate with fast velocity and have relatively weak dispersion and attenuation, while the second types of waves behave as diffusive modes due to their distinct dispersion and strong attenuation. The second S wave resulting from the bulk and shear viscous loss within pore fluid is slower than the second P wave but with strong attenuation at lower frequencies. Based on the simplified porous elastic equations, the effects of petrophysical parameters (permeability, porosity, coupling density and fluid viscosity) on the velocity dispersion and attenuation of P and S waves are studied in brine‐saturated sandstone compared with the results of Biot's theory. The results show that the dispersion and attenuation of P waves in simplified theory are stronger than those of Biot's theory and appear at slightly lower frequencies because of the existence of bulk and shear viscous loss within pore fluid. The properties of the first S wave are almost consistent with the S wave in Biot's theory, while the second S wave not included in Biot's theory even dies off around its source due to its extremely strong attenuation. The permeability and porosity have an obvious impact on the velocity dispersion and attenuation of both P and S waves. Higher permeabilities make the peaks of attenuation shift towards lower frequencies. Higher porosities correspond to higher dispersion and attenuation. Moreover, the inertial coupling between fluid and solid induces weak velocity dispersion and attenuation of both P and S waves at higher frequencies, whereas the fluid viscosity dominates the dispersion and attenuation in a macroscopic porous medium. Besides, the heavy oil sand is used to investigate the influence of high viscous fluid on the dispersion and attenuation of both P and S waves. The dispersion and attenuation in heavy oil sand are stronger than those in brine‐saturated sandstone due to the considerable shear viscosity of heavy oil. Seismic properties are strongly influenced by the fluid viscosity; thus, viscosity should be included in fluid properties to explain solid–fluid combination behaviour properly.  相似文献   
5.
Oyster reefs and their spatial patterns are deemed to change the local hydrodynamic condition and exert profound impacts on the grain size, concentration and transportation of suspended sediments. Meanwhile, high suspended sediment concentration often results in excess mortality among oysters. Oyster reefs are rare and vital ecosystem in Liyashan national marine park, Jiangsu Coast, China. However, urgent conservation efforts should be made on account of the drastic reduction in reef areas. To investigate the sediment dynamics and the geomorphology, two tripod observation systems were deployed and UAV aerial surveys with elevation measurement using Real Time Kinematic (RTK) were also carried out. High mud content (60%) was found in the bed sediment at the reef ridge, causing much lower drag coefficient than other recorded values of living oyster reefs, indicating the death of oysters and the degradation of reefs in Liyashan. Ridgelines of the string reefs at 45° to the current direction and high suspended sediment concentration in the water body (50–370 mg/L) that exceeds the threshold (200 mg/L), which would affect nutrient uptake efficiency and further result in gill saturation, decrease of clearance rate and associated deposition, were probably crucial causes of the death of oysters. The findings are useful for restoring natural oyster reefs and designing artificial reefs for nature-based coastal defense.  相似文献   
6.
研究汛期短时强降水特征,对于南方低山丘陵地区山洪灾害的预报具有重要指导意义。以怀化市为研究区域,基于该区域11个国家站和403个区域自动气象站的2012-2017年4-9月期间逐小时降水量以及相对应的NCEP资料,分析了怀化市短时强降水的时空分布特征,得出了产生短时强降水天气系统模型,结果显示:①汛期短时强降水发生频率较高,时间集中,分布不均。主要出现在5~7月,占4~9月的72.9%,其次在8~9月;北部频数多,中南部少,西部最少,辰溪、麻阳和怀化三县交界处及沅陵县的大合坪附近是频发区域。②短时强降水日变化呈单峰型,4~10时最容易发生,峰值在8时,谷值在23时。③强度越强出现的频次越少;北部的强度和次数大于其它区域;50~79.9 mm/h,占总站数的68.4%;各月国家站的极值乘以2约等于区域站极值。④低涡型短时强降水出现概率最高,低涡位置和移动路径是短时强降水预报的关键点。  相似文献   
7.
Groundwater in India plays an important role to support livelihoods and maintain ecosystems and the present rate of depletion of groundwater resources poses a serious threat to water security. Yet, the sensitivity of the hydrological processes governing groundwater recharge to climate variability remains unclear in the region. Here we assess the groundwater sensitivity (precipitation–recharge relationship) and its potential resilience towards climatic variability over peninsular India using a conceptual water balance model and a convex model, respectively in 54 catchments over peninsular India. Based on the model performance using a comprehensive approach (Nash Sutcliffe Efficiency [NSE], bias and variability), 24 out of 54 catchments are selected for assessment of groundwater sensitivity and its resilience. Further, a systematic approach is used to understand the changes in resilience on a temporal scale based upon the convex model and principle of critical slowing down theory. The results of the study indicate that the catchments with higher mean groundwater sensitivity (GWS) encompass high variability in GWS over the period (1988–2011), thus indicating the associated vulnerability towards hydroclimatic disturbances. Moreover, it was found that the catchments pertaining to a lower magnitude of mean resilience index incorporates a high variability in resilience index over the period (1993–2007), clearly illustrating the inherent vulnerability of these catchments. The resilience of groundwater towards climatic variability and hydroclimatic disturbances that is revealed by groundwater sensitivity is essential to understand the future impacts of changing climate on groundwater and can further facilitate effective adaptation strategies.  相似文献   
8.
Time series of hydrogen and oxygen stable isotope ratios (δ2H and δ18O) in rivers can be used to quantify groundwater contributions to streamflow, and timescales of catchment storage. However, these isotope hydrology techniques rely on distinct spatial or temporal patterns of δ2H and δ18O within the hydrologic cycle. In New Zealand, lack of understanding of spatial and temporal patterns of δ2H and δ18O of river water hinders development of regional and national-scale hydrological models. We measured δ2H and δ18O monthly, together with river flow rates at 58 locations across New Zealand over a two-year period. Results show: (a) general patterns of decreasing δ2H and δ18O with increasing latitude were altered by New Zealand's major mountain ranges; δ2H and δ18O were distinctly lower in rivers fed from higher elevation catchments, and in eastern rain-shadow areas of both islands; (b) river water δ2H and δ18O values were partly controlled by local catchment characteristics (catchment slope, PET, catchment elevation, and upstream lake area) that influence evaporation processes; (c) regional differences in evaporation caused the slope of the river water line (i.e., the relationship between δ2H and δ18O in river water) for the (warmer) North Island to be lower than that of the (cooler, mountain-dominated) South Island; (d) δ2H seasonal offsets (i.e., the difference between seasonal peak and mean values) for individual sites ranged from 0.50‰ to 5.07‰. Peak values of δ18O and δ2H were in late summer, but values peaked 1 month later at the South Island sites, likely due to greater snow-melt contributions to streamflow. Strong spatial differences in river water δ2H and δ18O caused by orographic rainfall effects and evaporation may inform studies of water mixing across landscapes. Generally distinct seasonal isotope cycles, despite the large catchment sizes of rivers studied, are encouraging for transit time analysis applications.  相似文献   
9.
以某高速铁路线上一座连续梁桥为例,运用模糊综合评判法,结合基于位移的支座损伤分析和截面曲率的桥墩损伤分析,以全概率理论地震损失模型为基础,提出了基于模糊理论的桥梁系统地震经济风险评估方法。结果表明:综合考虑桥梁系统的模糊地震经济风险分析方法能更全面地计算出连续梁桥在地震作用下的经济损失,仅以桥墩构件代表全桥所得地震经济损失误差较大。基于模糊理论的年预期损失风险框架方法通过结构抗震性能的概率特征可对高速铁路连续梁桥的地震直接经济风险进行全面评估,为该类桥梁的抗震设计、维修加固和灾后重建等方案做出合理评价。  相似文献   
10.
以广东省揭阳市土壤为研究对象,采集了表层土壤(0~20 cm)样1 330个和深层土壤(>150 cm)样331个,测定了土壤Pb含量。利用GIS空间分析技术、半变异函数拟合和方差分析等方法研究土壤Pb含量的空间结构、特征和影响因素。结果显示: 揭阳市不存在明显的土壤Pb污染,表层土壤Pb含量平均值39.26 mg/kg,低于揭阳市土壤Pb背景值(43.71 mg/kg),略高于广东省土壤Pb背景值(36.00 mg/kg);富集因子表明研究区表层土壤Pb富集程度主要为无富集和轻微富集,分别占52.11%和42.63%,Pb富集不明显;研究区表层土壤Pb空间分布呈中等自相关性;表层土壤Pb高值区主要分布在人类活动影响强烈的东部和南部地区。按土地利用、成土母质、土壤类型及其理化性质的分类统计表明,林地及未利用地表层土壤Pb含量最高;页岩风化形成的土壤Pb含量显著高于其他成土母质区土壤;黄壤Pb含量相对较高;有机碳和pH值均与土壤Pb含量呈显著正相关。  相似文献   
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