Instability model for recurring large and great earthquakes in southern California     

William D. Stuart 《Pure and Applied Geophysics》1984,122(6):793-811

The locked section of the San Andreas fault in southern California has experienced a number of large and great earthquakes in the past, and thus is expected to have more in the future. To estimate the location, time, and slip of the next few earthquakes, an earthquake instability model is formulated. The model is similar to one recently developed for moderate earthquakes on the San Andreas fault near Parkfield, California. In both models, unstable faulting (the earthquake analog) is caused by failure of all or part of a patch of brittle, strain-softening fault zone. In the present model the patch extends downward from the ground surface to about 12 km depth, and extends 500 km along strike from Parkfield to the Salton Sea. The variation of patch strength along strike is adjusted by trial until the computed sequence of instabilities matches the sequence of large and great earthquakes sincea.d. 1080 reported by Sieh and others. The last earthquake was theM=8.3 Ft. Tejon event in 1857. The resulting strength variation has five contiguous sections of alternately low and high strength. From north to south, the approximate locations of the sections are: (1) Parkfield to Bitterwater Valley, (2) Bitterwater Valley to Lake Hughes, (3) Lake Hughes to San Bernardino, (4) San Bernardino to Palm Springs, and (5) Palm Springs to the Salton Sea. Sections 1, 3, and 5 have strengths between 53 and 88 bars; sections 2 and 4 have strengths between 164 and 193 bars. Patch section ends and unstable rupture ends usually coincide, although one or more adjacent patch sections may fail unstably at once. The model predicts that the next sections of the fault to slip unstably will be 1, 3, and 5; the order and dates depend on the assumed length of an earthquake rupture in about 1700.  相似文献   

Hillslope gullying in the Solway Firth — Morecambe Bay region, Great Britain: Responses to human impact and/or climatic deterioration?     

R.C. Chiverrell  A.M. Harvey  G.C. Foster 《Geomorphology》2007,84(3-4):317

In the Solway Firth — Morecambe Bay region of Great Britain there is evidence for heightened hillslope instability during the late Holocene (after 3000 cal. BP). Little or no hillslope geomorphic activity has been identified occurring during the early Holocene, but there is abundant evidence for late Holocene hillslope erosion (gullying) and associated alluvial fan and valley floor deposition. Interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500–2200, 1300–1000, 1000–800 and 500 cal. BP. Both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds: and palaeoecological data on climatic change (bog surface wetness) and human impact (pollen), together with archaeological and documentary evidence of landscape history, provide a context for addressing the causes of late Holocene geomorphic instability. High magnitude storm events are the primary agent responsible for gully incision, but neither such events nor cooler/wetter climatic episodes appear to have produced gully systems in the region before 3000 cal. BP. Increased gullying after 2500–2200 cal. BP coincides with population expansion during Iron Age and Romano-British times. The widespread and extensive gullying after 1300–1000 cal. BP and after 1000–800 cal. BP coincides with periods of population expansion and a growing rural economy identified during Norse times, 9–10th centuries AD, and during the Medieval Period, 12–13th centuries AD. These periods were separated by a downturn associated with the ‘harrying of the north’ AD 1069 to 1070. The gullying episode after 500 cal. BP also coincides with increased anthropogenic pressure on the uplands, with population growth and agricultural expansion after AD 1500 following 150 years of malaise caused by livestock and human (the Black Death) plagues, poor harvests and conflicts on the Scottish/English border. The increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late Holocene, and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events. In particular, the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion, and the hillslope gullying record in the region, therefore, contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape.  相似文献   

水平切变线上涡层不稳定理论   总被引：25，自引：4，他引：25  

高守亭  周玉淑 《气象学报》2001,59(4):393-404

文中打破了传统的 Kelvin- Helmholtz研究切变不稳定的观点 ,考虑了强涡度切变存在时切变线已构成了一个涡层 ,这时切变线的不稳定问题就变为涡层的不稳定问题。同时考虑由涡层所产生的诱导速度 ,从理论上得到了水平切变线上涡层不稳定必要条件的判据 ,即必须满足 (1 - Rv Rid) >0 ,且有 U(y,t) >U(A(t) )与之相配合。这表明环境场的配置制约着切变线上扰动的发展 ,这种中尺度扰动同环境场存在着相互作用。文中还用具体个例对如何计算不稳定必要条件做了解释和说明。  相似文献   

Pore scale modeling of immiscible and miscible fluid flows using smoothed particle hydrodynamics     

Alexandre M. Tartakovsky  Paul Meakin 《Advances in water resources》2006

A numerical model based on smoothed particle hydrodynamics (SPH) was developed and used to simulate immiscible and miscible fluid flows in porous media and to study effects of pore scale heterogeneity and anisotropy on such flows.  相似文献   

On the evolution of finite-amplitude disturbance to the barotropic and baroclinic quasigeostrophic flows     

Mu Mu  Xiang Jie 《大气科学进展》1998,15(1):113-123

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Influence of Vertical Shear of Basic Tangential Wind on the Development and Maintenance of Typhoon          下载免费PDF全文

TAO Jianjun  WANG Fang  LI Chaokui  HU Xianghui 《Acta Meteorologica Sinica》2013,27(2):273-281

By using a linear symmetric Conditional Instability of Second Kind (CISK) model containing basic flow, we study the interactions between basic flow and mesoscale disturbances in typhoon. The result shows that in the early stage of typhoon formation, the combined action of vertical shear of basic flow at low level and CISK impels the disturbances to grow rapidly and to move toward the center of typhoon. The development of disturbances, likewise, influences on typhoon’s development and structure. Analysis of the mesoscale disturbances’ development and propagation indicates that the maximum wind region moves toward the center, wind velocity increases, and circulation features of an eye appear. Similarly, when a typhoon decays, the increase of low-level vertical wind shear facilitates the development of mesoscale disturbances. In turn, these mesoscale disturbances will provide typhoon with energy and make the typhoon intensify again. Therefore, it can be said that typhoon has the renewable or self-repair function.  相似文献   

The erodibility of some Nigerian soils: A comparison of rainfall simulator results with estimates obtained from the Wischmeier nomogram     

A. Vanelslande  R. Lal  D. Gabriels 《水文研究》1987,1(3):255-265

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Instability of exogenous lava lobes during intense rainfall   总被引：1，自引：1，他引：0  

John?SimmonsEmail author  Derek?Elsworth  Barry?Voight 《Bulletin of Volcanology》2004,66(8):725-734

On many volcanoes, there is evidence of a relationship between dome collapse and periods of high precipitation. We propose a mechanism for this relationship and investigate the conditions that optimize failure by this process. Observations of elongate lobes that evolve through exogenous growth of lava domes reveal that they commonly develop tensile fractures perpendicular to the direction of motion. These cracks can increase in depth by localized cooling and volumetric contraction. During periods of high rainfall, water can fill these cracks, and the increase in fluid pressure on the base of the lobes and within the crack can trigger the collapse of the hot exogenous lava domes. Using limit-equilibrium analysis, it is possible to calculate the water and vapor forces acting on the rear and base of the potentially unstable part of the lobe. The model presented is rectangular in cross-section, with material properties representative of andesitic dome rocks. Vapor pressures at the base of cracks are sealed by the penetrating rainfall, which forms a saturated cap within the lobe. This leads to an increase in fluid pressurization both through the underlying gas pressure and the downslope component of the liquid water cap. Fluid pressurization increases as the penetration depth increases. This rainfall penetration depth is dependent on the thermal properties of the rocks, antecedent temperature, lobe geometry, and the intensity and duration of precipitation. Dominant parameters influencing the stability of the lobe are principally lobe thickness, duration and intensity of rainfall, and antecedent lobe temperature. Our modeling reveals that thicker lobes are intrinsically more unstable due to the amplification of downslope forces in comparison to cohesive strength. The increase in the duration and intensity of rainfall events also increases the potential for collapse, as it leads to deeper liquid penetration. Deeper penetration depths are also achieved through lower antecedent temperatures since less fluid is lost through vaporization. Thus, the potential for rain-triggered collapse increases with time from emplacement.Editorial responsibility: D. Dingwell  相似文献   

江西夏季雷电天气热力条件及不稳定指数对比分析   总被引：1，自引：0，他引：1  

郑婧  许爱华  应冬梅  刘芳 《气象与减灾研究》2009,32(2):27-32,F0003

选取2007年夏季两次强度不同的致灾雷电过程进行对比,并将其能量参数与典型历史个例进行比较。结果表明：（1）副高位置、500hPa低槽移速、中尺度辐合系统以及热力结构的差异是导致雷暴强度不同的原因之一;（2）中尺度辐合系统移向鄱阳湖时,对流天气更加剧烈,但对大尺度系统鄱阳湖的阻挡作用不显著;（3）对流层上干下湿的特征越明显,强雷电发生的概率越大;（4）CAPE〉632J/kg,K〉34℃,Si〈0℃,Li〈0℃,TT〉43℃,SSI〉43可以作为江西致灾雷电发生的阈值,超过阈值越多,强对流天气发生的概率越大;（5）能量参数的演变对致灾雷电的潜势预测、强度判别具有较好的指示,夏季对流参数的指示意义较春季更好。  相似文献   

近50年中国冬季气温对ENSO响应的时空稳定性分析研究   总被引：2，自引：0，他引：2  

韩文韬  卫捷  沈新勇 《气候与环境研究》2014,19(1):97-106

根据1962~2010年中国160站的月平均气温资料、Ni?o3.4区海洋Ni?o指数(ONI)资料以及相应的NECP/NCAR再分析资料,采用相关分析、滑动相关分析、滑动t检验、合成分析等方法,探讨了最近50年中国冬季气温对ENSO响应的时空稳定性问题。结果表明:中国冬季气温异常对ENSO的响应有着显著的地域性差异以及年代际变化,其中东北和西南地区的相关关系不稳定度比较大,而在中国东部地区则比较稳定。东北与西南地区在20世纪70年代中后期以后,冬季气温对ENSO的响应迅速减弱,甚至发生了反向变化,而东部地区这种关系近50年并没有较强的突变。相应的亚洲高空大气环流对ENSO的响应也具有明显的空间差异和阶段性变化,其特征与中国冬季气温对ENSO的响应特征基本对应。从大气环流角度解释中国冬季气温对ENSO的响应发生阶段性减弱的可能机制:ENSO通过经向Hadley环流影响中高纬度大气环流,由于70年代中后期以后亚洲经向Hadley环流的下沉支发生显著减弱,使得东亚大气环流对ENSO的响应减弱,进而导致中国冬季气温对ENSO的响应减弱。  相似文献