The precursory earthquake swarm

Prior swarms near the sites of eleven moderate to large earthquakes from diverse tectonic settings in the New Zealand and California regions yield regressions for the estimation of magnitude and time of occurrence, and thus offer a possible basis for long-range forecasting.     

Long-range earthquake forecasting based on a single predictor

Summary. For a long-term predictor from which a joint distribution of earthquake occurrence time and magnitude has been obtained, and also a record of past successes, false alarms and failures, Bayesian statistical methods yield predictive information of the kind needed as a basis for decision-making on precautionary measures. The information is presented in terms of risk refinement, intensity probability and success probability. After the event the relative likelihood that a prediction was a success or failure can be estimated. Comparisons can also be made of the performance of different forecasting models. The application of these methods is illustrated by an example based on the proposed swarm-magnitude predictor.     

Evaluation of recent hydro-climatic changes in four tributaries of the Niger River Basin (West Africa)

West Africa experienced severe drought during the 1970s and 1980s, posing a threat to water resources. A wetter climate more recently suggests recovery from the drought. The Mann-Kendall trend and Theil-Sen’s slope estimator were applied to detect probable trends in weather elements in four sub-basins of the Niger River Basin between 1970 and 2010. The cross-entropy method was used to detect breakpoints in rainfall and runoff, Spearman’s rank test for correlation between the two, and cross-correlation analysis for possible lags. Results showed an overall increase in rainfall and runoff and a decrease in sunshine duration. Spearman’s coefficients suggest significant (5%) moderate to strong rainfall–runoff correlation for three sub-basins. A significant lower runoff was observed around 1979, with a rainfall break around 1992, indicating possible cessation of the drought. Temperatures increased significantly, at 0.02–0.05°C year^-1, with a negative wind speed trend for most stations. Half of the stations exhibited an increase in potential evapotranspiration.

EDITOR M.C. Acreman

ASSOCIATE EDITOR Not assigned     

白云鄂博碳酸岩的方解石-白云石地质温度计

利用方解石-白云石地质温度计对白云鄂博地区碳酸岩的平衡温度进行了测定。出露于东矿下盘的白云岩质火山岩和出露于尖山的方解石-白云石型火山岩获得了较高的温度,分别为681℃和648℃。这些样品中的方解石呈二十微米左右晶形较完整的小片,被稍大粒度的白云石颗粒包裹,未受交代作用影响,推测这种碳酸岩在快速冷却的情况下保存下了其岩浆侵位时的成分特点,从而指示出接近碳酸岩浆侵位时的温度。但本区多数碳酸岩的平衡温度在400～500℃之间,有下列三种情况:(1)具有自形-半自形中粗粒粒状变晶结构的碳酸岩最后的平衡温度为415～496℃;(2)产自东矿的其余样品(火山岩),所测最后平衡温度为431～485℃,在测温的微区范围内可见极细粒白云石方解石与稀土等矿物共生的现象;(3)为交代重结晶结构的碳酸岩明显受到后期热液流体的交代,在流体的作用下共生方解石和白云石在成分上达到新的平衡,平衡温度为432～507℃。本文所分析的样品多数结果(371～507℃)与用白云石(方解石)和磁铁矿氧同位素温度计对白云鄂博碳酸岩的计算结果(360～546℃)十分一致。虽然有研究者对方解石-白云石温度计用于火成碳酸岩表示过质疑,但本文资料表明火成碳酸岩最后的平衡温度是可以运用方解石-白云石温度计法来计算的。     

陕西省略阳县杨家坝多金属矿区成矿作用地球化学示踪

本文以陕西省略阳县杨家坝多金属矿区为例,通过对该矿区岩(矿)石和各类脉体的岩相学、稀土和微量元素及流体包裹体地球化学示踪发现,多金属中重晶石的形成及硅化、碳酸盐化、滑石化、纤闪石化、绢云母化和绿泥石化和透闪石岩的含氟浅闪石及隐晶硅质玻璃和微晶硅质,这表明与成矿蚀变有关的热液流体是一种不同于一般地壳流体的富硅、钛、铁、碱质和挥发份,并具备熔体性质的成矿流体。各类样品的稀土元素配分模式明显富集LREE,在Ce、Eu、Yb异常的组合上也各具特征。LREE富集是地幔流体作用的显著特征之一;矿石和脉体的负Ce、正Eu和负Yb异常以及流体包裹体中H2O-C6H6成分,是高温还原地幔流体的重要标志;正Ce和负Eu异常的出现,以及Ce、Eu、Yb异常的减弱和消失则是壳幔混染叠加改造的显示。综合研究表明:矿区成矿过程可能统一受制于秦岭地区碰撞造山背景下具高温还原性质的地幔流体作用,且由此引发壳幔强烈混染的叠加改造作用在成矿过程中发挥了重要作用。     

Bathing water quality in the North sea,and the Mediterranean

The bacteriological quality of bathing waters is examined for two coastlines with very different environmental characteristics, namely Whitley Bay in the north east of England and the Bay of Naples in the Mediterranean. The Whitley Bay beach is contaminated by sea outfalls, but tidal action is vigorous, the water is cool and sunlight is not very strong. The water does not meet the EEC standards for bathing water quality at the present time, but a new sewerage system soon to be completed should effect a substantial improvement.In the Bay of Naples there is very little tide, the water is warm and sunlight is usually strong in the bathing season. The water quality meets the EEC standards for most of the authorized beaches and pollution is restricted to a few well defined zones in the Bay.     

Long-range Earthquake Forecasting with Every Earthquake a Precursor According to Scale

Scaling relations previously derived from examples of the precursory scale increase before major earthquakes show that the precursor is a long-term predictor of the time, magnitude, and location of the major earthquake. These relations are here taken as the basis of a stochastic forecasting model in which every earthquake is regarded as a precursor. The problem of identifying those earthquakes that are actually precursory is thus set aside, at the cost of limiting the strength of the resulting forecast. The contribution of an individual earthquake to the future distribution of hazard in time, magnitude and location is on a scale determined, through the scaling relations, by its magnitude. Provision is made for a contribution to be affected by other earthquakes close in time and location, e.g., an aftershock may be given low weight. Using the New Zealand catalogue, the model has been fitted to the forecasting of shallow earthquakes exceeding magnitude 5.75 over the period 1965–2000. It fits the data much better than a baseline Poisson model with a location distribution based on proximity to the epicenters of past earthquakes. Further, the model has been applied, with unchanged parameters, to the California region over the period 1975–2001. There also, it performs much better than the baseline model fitted to the same region over the period 1951–1974; the likelihood ratio is 10¹⁵ in favor of the present model. These results lend credence to the precursory scale increase phenomenon, and show that the scaling relations are pervasive in earthquake catalogues. The forecasting model provides a new baseline model against which future refinements, and other proposed models, can be tested. It may also prove to be useful in practice. Its applicability to other regions has still to be established.