Extending earthquakes' reach through cascading

Earthquakes, whatever their size, can trigger other earthquakes. Mainshocks cause aftershocks to occur, which in turn activate their own local aftershock sequences, resulting in a cascade of triggering that extends the reach of the initial mainshock. A long-lasting difficulty is to determine which earthquakes are connected, either directly or indirectly. Here we show that this causal structure can be found probabilistically, with no a priori model nor parameterization. Large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration. Relative to these large mainshocks, small earthquakes collectively have a greater effect on triggering. Hence, cascade triggering is a key component in earthquake interactions.     

Mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock-aftershock interaction

The diverse aftershock sequence of the 1989 Loma Prieta earthquake is inconsistent with conventional models of mainshock-aftershock interaction because the aftershocks do not accommodate mainshock-induced stress changes. Instead, the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane. This orientation implies that (i) stress drop in the mainshock was nearly complete, (ii) mainshock-induced decreases of fault strength helped were important in controlling the occurrence of after-shocks, and (iii) mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip.     

Near-field investigations of the landers earthquake sequence, april to july 1992

The Landers earthquake, which had a moment magnitude (M(w)) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M(w) 6.1 preshock and M(w) 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.     

Replication of apparent nonlinear seismic response with linear wave propagation models

It is necessary to understand ground-motion amplification by sediment, defined as the ratio of ground motions at sediment sites to those at rock sites, to predict seismic loadings for earthquake engineering. At sediment sites, observed weak-motion amplifications from magnitude 3 to 4 aftershocks of the 1994 Northridge earthquake were twice as large as magnitude 6.7 mainshock amplifications. Amplitude-dependent (nonlinear) amplification by sediment is one explanation. However, earthquake simulations with empirical impulse responses and elastic finite-difference calculations with weakly heterogeneous, random three-dimensional (3D) crustal velocity variations show that linear wave propagation can explain observed (apparently nonlinear) sediment responses. Random 3D velocity variations also reproduce the observed log-normal dispersion of peak ground motions. Deterministic wave propagation models are not adequate to quantify the scaling and dispersion of near-source ground motions.     

Propagation of slow slip leading up to the 2011 M(w) 9.0 Tohoku-Oki earthquake

Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point. The second sequence, which involved large slip rates, may have caused substantial stress loading, prompting the unstable dynamic rupture of the mainshock.     

Seismicity remotely triggered by the magnitude 7.3 landers, california, earthquake

The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).     

Aftershocks and intensity of the managua earthquake of 23 december 1972

Two portable seismic stations and a fixed array of five seismometers were used to record aftershocks in the vicinity of Managua, Nicaragua, after the earthquake of 23 December 1972. Approximately 3000 aftershocks were recorded during a 20-day period in January 1973. Left lateral motion along at least two faults, both trending N40 degrees E, is inferred from the seismic data. This is in good agreement with dislocations mapped at the surface in Managua. The data suggest that the shallow earthquakes of the Managua region are a consequence of north-south compressional stresses and east-west tensional stresses. This is consistent with regional plate movements deduced in other investigations.     

When is an island community in equilibrium?

To determine whether the number of species in a biota is in equilibrium requires a colonization model. In a simple Markov model, each species' extinction and immigration probabilities are estimated independently from available data. For one inland and two island avifaunas, a simulation with these probabilities shows that the trajectories of species richness through time do not manifest the regulatory tendencies expected if species interactions cause species richness to be continuously redressed toward an equilibrium.     

具有相依结构离散时间模型破产概率的上界

研究两类具有相依结构的离散时间风险模型的破产概率问题.其中,索赔和利率过程假设为2个不同的自回归移动平均模型.利用更新递归技巧,首先得到了该模型下破产概率所满足的递归方程.然后,根据该递归方程得到了破产概率的上界估计.最后对两类风险模型的破产概率的上界进行了比较.     

基于浅层语义的农业FAQ检索系统

本文提出了一种基于浅层语义的FAQ检索模型.该模型以自然语言为接口,利用"知网"和农业本体,首先从用户输入中抽取农业领域概念词,然后根据这些概念词从系统数据库中检索出一个候选QA对的小集合,通过计算输入问句与候选QA对的语义相似度,选择一些与输入问句接近的问题,以及对应的答案返给用户.     

Stress triggering of the 1994 m = 6.7 northridge, california, earthquake by its predecessors

A model of stress transfer implies that earthquakes in 1933 and 1952 increased the Coulomb stress toward failure at the site of the 1971 San Fernando earthquake. The 1971 earthquake in turn raised stress and produced aftershocks at the site of the 1987 Whittier Narrows and 1994 Northridge ruptures. The Northridge main shock raised stress in areas where its aftershocks and surface faulting occurred. Together, the earthquakes with moment magnitude M >/= 6 near Los Angeles since 1933 have stressed parts of the Oak Ridge, Sierra Madre, Santa Monica Mountains, Elysian Park, and Newport-lnglewood faults by more than 1 bar. Although too small to cause earthquakes, these stress changes can trigger events if the crust is already near failure or advance future earthquake occurrence if it is not.     

Regular intervals between hawaiian earthquakes: implications for predicting the next event

During the years 1941 through 1983 five earthquake mainshocks of moderate magnitude occurred at regular intervals of 10.5 +/- 1.5 years within a 6-kilometer radius in Hawaii. It is proposed that these Kaoiki earthquakes will continue to occur at regular intervals because the strain accumulation rate and the strained volume remain constant. With appropriate instrumentation, it may be possible to refine predictions of subsequent Kaoiki earthquakes.     

Frictional afterslip following the 2005 Nias-Simeulue earthquake, Sumatra

Continuously recording Global Positioning System stations near the 28 March 2005 rupture of the Sunda megathrust [moment magnitude (Mw) 8.7] show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust, with a major fraction of this slip in the up-dip direction from the main rupture. Eleven months after the main shock, afterslip continues at rates several times the average interseismic rate, resulting in deformation equivalent to at least a M(w) 8.2 earthquake. In general, along-strike variations in frictional behavior appear to persist over multiple earthquake cycles. Aftershocks cluster along the boundary between the region of coseismic slip and the up-dip creeping zone. We observe that the cumulative number of aftershocks increases linearly with postseismic displacements; this finding suggests that the temporal evolution of aftershocks is governed by afterslip.     

The aftershock signature of supershear earthquakes

Recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks. This supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane. This shock wave may increase the destruction caused by the earthquake. We report that supershear earthquakes are characterized by a specific pattern of aftershocks: The fault plane itself is remarkably quiet whereas aftershocks cluster off the fault, on secondary structures that are activated by the supershear rupture. The post-earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments, whereas the activation of off-fault structures is explained by the shock wave radiation, which produces high stresses over a wide zone surrounding the fault.     

Coastal uplift and mortality of intertidal organisms caused by the september 1985 Mexico earthquakes

Coastal uplift associated with the great Mexican earthquake of 19 September 1985 and its principal aftershock produced widespread mortality of intertidal organisms along the coast of the states of Michoacán and Guerrero, Mexico. Measurements of the vertical extent of mortality at ten sites provided estimates of the magnitude of the vertical component of deformation along the coast. Within the affected area, uplift ranged from about 12 centimeters to about 1 meter, and no subsidence was observed. The observations are consistent with models of the tectonic deformation that results from buried slip on a shallow-dipping underthrust fault.     

A modular steel freeway bridge: design concept and earthquake resistance

A modular multilane steel freeway bridge has been constructed from surplus railroad flatcar decks. It can be erected on-site in a few days' time. It has been built and static-load tested for emergency freeway bridge repair. This inexpensive modular bridge may also have broad application around the world for low-cost bridges in areas where funds are limited. On the basis of static-load testing performed by the California Department of Transportation and computer dynamic analysis, this simple modular-design concept has the potential of providing a strong bridge that can withstand the severe aftershocks expected immediately after a major earthquake.     

Aftershocks caused by pore fluid flow?

Large shallow earthquakes can induce changes in the fluid pore pressure that are comparable to stress drops on faults. The subsequent redistribution of pore pressure as a result of fluid flow slowly decreases the strength of rock and may result in delayed fracture. The agreement between computed rates of decay and observed rates of aftershock activity suggests that this is an attractive mechanism for aftershockss.     

索赔为稀疏过程的二维风险模型的破产概率

研究了二维风险模型,其中保单到达是复合Poisson-Geometric过程,且索赔发生是保单到达过程的q-稀疏过程.对二维模型定义了3种不同的破产概率,并运用一维风险模型的相关理论得到了3种破产概率的明确表达式或者上界.     

近天然落叶松云冷杉林单木枯损模型研究

为了预测近天然落叶松云冷杉林的生长和发展,该文建立了近天然落叶松云冷杉林中长白落叶松、红松、云冷杉、中阔和慢阔5个树种（组）的单木枯损模型。数据来自于20个长期固定观测样地,共得到12 853个观测数据,其中80%的数据用于建模,20%的数据用于模型验证。采用Logistic回归方法,考虑多重共线性逐步筛选出对枯损有显著影响的自变量;根据预测结果敏感度和特异度的最大和原则(MST原则)确定模型的概率阈值。结果表明:①起初胸径、竞争指数、林分密度、多样性指数、立地因子都是显著影响树木枯损的因子,但不同树种的影响因子各异。②起初胸径在所有模型中均极显著;竞争指数除在红松和慢阔模型中未进入模型外,在其他模型中均显著;林分密度和多样性指数在长白落叶松和慢阔模型中显著;立地因子在长白落叶松模型中极显著。③除红松、中阔模型由于参与建模数据过少而无法通过χ2检验外,其余分树种模型都有良好的解释性和预测性。④模型诊断的AUC值在0.618～0.815之间。因此,建立的不同树种的单木枯损模型可为近天然落叶松云冷杉林的生长预测提供依据。      

Integrated uncertain models for runoff forecasting and crop planting structure optimization of the Shiyang River Basin,north-west China

To improve the accuracy of runoff forecasting, an uncertain multiple linear regression (UMLR) model is presented in this study. The proposed model avoids the transfer of random error generated in the independent variable to the dependent variable, as this affects prediction accuracy. On this basis, an inexact two-stage stochastic programming (ITSP) model is used for crop planting structure optimization (CPSO) with the inputs that are interval flow values under different probabilities obtained from the UMLR model. The developed system, in which the UMLR model for runoff forecasting and the ITSP model for crop planting structure optimization are integrated, is applied to a real case study. The aim of the developed system is to optimize crops planting area with limited available water resources base on the downstream runoff forecasting in order to obtain the maximum system benefit in the future. The solution obtained can demonstrate the feasibility and suitability of the developed system, and help decision makers to identify reasonable crop planting structure under multiple uncertainties.