Meteorological triggering of earthquake swarms at Mt. Hochstaufen, SE-Germany

A growing body of evidence suggests that fluids are intimately linked to a variety of faulting processes. Yet, the particular mechanisms through which fluids and associated parameters influence the stress regime and thus the seismicity of a particular area are not well understood.We carry out a study of the spatio-temporal behavior of earthquakes, fluid-related parameters (groundwater levels) and meteorological observables (precipitation) in the swarm earthquake area of Bad Reichenhall, southeastern Germany. The small volume in which the earthquakes take place, almost yearly occurring earthquake swarms and a permanent, seismo-meteorological monitoring network, provide nearly controlled experimental conditions to study the physics of earthquake swarms and to infer characteristic properties of the seismogenic crust.In this paper we (1) describe this fairly unique study area in terms of geology, seismicity and atmospheric conditions; (2) present two cases of earthquake swarms that seem to follow above-average rainfall events; and (3) examine the observed migration of hypocenters with a simple pore pressure diffusion model.We find significant correlation of seismicity with rainfall and groundwater level increase, and estimate an average hydraulic diffusivity of D = 0.75 ± 0.35 m²/s for Mt. Hochstaufen in 2002.     

Influence of streambed hydraulic conductivity on solute exchange with the hyporheic zone

A conservative solute tracer experiment was conducted in Indian Creek, a small urban stream in Philadelphia, Pennsylvania to investigate the role of subsurface properties on the exchange between streamwater and the hyporheic zone (subsurface surrounding the stream). Sodium Bromide (NaBr) was used as a conservative tracer, and it was monitored in the surface water at two stations and in the upper bed sediments (shallow hyporheic zone extending from 7.5 to 10 cm below the streambed). The hydraulic conductivity (K) of the upper bed sediments and the lower bed sediments (10–12.5 cm below the streambed) was measured in situ. High tracer concentrations were observed in the upper layer at locations where the hydraulic conductivity of the upper layer was larger than that of the lower layer. Low concentrations in the upper layer were observed in the converse case. A statistically significant relationship between the mass retained in the upper layer and the difference of K values between layers was observed.     

From well-test data to input to stochastic continuum models: effect of the variable support scale of the hydraulic data

The question of how well the true underlying hydraulic conductivity statistics of heterogeneous media are captured by well tests is addressed. The hydraulic conductivity value and the corresponding support volume associated with a theoretical well are correlated, causing a bias in the statistics derived from well-test analyses. Statistics derived from numerically simulated well tests are compared with the known underlying conductivity statistics and the results indicate an under-prediction by simulations at higher hydraulic conductivities. The deviation starts at about mean conductivity and can be as large as an order of magnitude, with the conductivity in the vicinity of the well defining the upper boundary. In other words, the conductivity value interpreted from the well test cannot be larger than the value that the well test first encounters. Consequently, for data in this simulation exercise, the standard deviation, if only determined for the upper range of the conductivity values, would be underestimated by a factor of 1.6–2. While this specific range is likely to depend on the scale and degree of the underlying heterogeneity as well as the duration of the test, the results should be indicative of a more general behaviour and are likely to occur in other heterogeneous data as well.

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Resumen Se plantea la pregunta de qué tan bien son representadas en las pruebas de pozo, las estadísticas reales de conductividad hidráulica subyacente de medios heterogéneos. Son correlacionados el valor de conductividad hidráulica y el volumen de apoyo correspondiente asociado con un pozo teórico, causando una distorsión en las estadísticas derivadas del análisis de la prueba de pozo. Las estadísticas derivadas de las pruebas de pozo simuladas numéricamente son comparadas con las estadísticas de conductividad subyacente conocidas, y los resultados indican una sub-predicción por las simulaciones hechas con conductividades hidráulicas más altas. La desviación empieza casi con la conductividad media y puede ser tan grande como un orden de magnitud, con la conductividad en la vecindad del pozo definiendo el límite superior. En otras palabras, el valor de conductividad interpretado a partir de la prueba del pozo no puede ser más grande que el valor que la prueba de pozo encuentre primero. Por consiguiente, para los datos en este ejercicio de simulación, la desviación estándar, si solamente fue determinada para el rango superior de los valores de conductividad, se subestimaría en un factor de 1.6–2. Mientras es probable que este rango específico dependa de la escala y del grado de la heterogeneidad subyacente, así como de la duración de la prueba, los resultados deben ser indicativos de un comportamiento más general y son probables también de ocurrir en otros datos heterogéneos.

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Résumé Nous posons ici la question de savoir dans quelle mesure les statistiques de la conductivité hydraulique des milieux hétérogènes pourrait être révélée par des essais de puits. La valeur de la conductivité hydraulique et le volume capté correspondant sont corrélés, créant un biais dans l’analyse des statistiques dérivées des essais de puits. Les statistiques en provenance de simulations numériques d’essais de puits sont comparées avec les statistiques de conductivités connues et les résultats indiquent une sous-évaluation par les simulations, pour les conductivités hydrauliques les plus élevées: la déviation commence à partir de la valeur moyenne de la conductivité et peut atteindre la magnitude d’un ordre de grandeur en considérant la conductivité mesurée au voisinage du puits. Autrement dit, la valeur de la conductivité interprétée via l’essais de pompage ne peut être plus importante que les premières valeurs rencontrées. Par conséquence, pour les données de cet exercice de simulation, la déviation standard sera sous-estimée d’un facteur compris entre 1.6–2 pour les valeurs les plus élevées. Tandis que l’échelle spécifique de valeurs est dépendante de l’échelle et du degré de l’hétérogénéité souterraine, de même que de la durée du test, les résultats pourraient être indicatifs d’un comportement plus général et seraient sans doute observables dans d’autres cas de données hétérogènes.

     

水工建筑物抗震可靠度设计和分析用的随机地震输入模型

结合水工建筑物的特点,提出了一套可供水工建筑物抗震可靠度设计和分析应用参考的随机地震运输输入模型和参数。     

沧参1井热历史及成油气环境研究

本文通过Ｕ－Ｐｂ同位素地质年代学研究，指出沧参１井沉积地层中的物质来源是华北古陆；隐伏花岗岩侵位年龄为９９Ｍａ，来源于具下地壳特征的太古宙岩石的重熔。对奥陶系碳酸岩流体包裹体特征研究指出沧参１井流体包体类型可分为３大类、８个亚类，本区碳酸盐类岩石有机质丰富，应为一套生油储油较好的岩系。特别是通过不同深度１０个磷灰石样品裂变径迹表观年龄和径迹长度特征的研究，论述了本区古地温的变化，约在１４３Ｍａ前石炭二送纪地层中的磷灰石经历过完全的退火，这是二迭纪以下地层的第１次生油作用；９９Ｍａ花岗岩侵位，岩浆热对围岩中有机质的转化和油气的形成起了促进作用，这可作为第２次生油期；第三纪时因地壳下降，沉积了巨厚的第三系地层，这时磷灰石退火带范围（大致相当于生油带）约为１７００—３９００ｍ，古地温梯度为３．１℃／１００ｍ，这是本区第３次生油阶段。     

用云南下关测点的水压致裂结果分析地形起伏对应力测值的影响

本文以云南下关黄草坝的水压致裂应力测量结果为例,讨论了地形起伏对云南区应力测值的影响。结果表明,地形起伏对应力测值的绝对影响随深度的增加衰减缓慢,相对影响急剧减小。100米以内深度的应力测量,地形影响可能给测值带来10%以上的误差。云南区的水压致裂应力测量深达500米,是可以排除掉地形起伏的影响的。     

Bed load transport in braided gravel-bed stream models

Bed load transport rate was measured in ten self-formed small-scale gravel braided streams developed in a laboratory flume at several different values of steady discharge and flume gradient. The streams are approximate Froude models of typical prototype braided streams but of no particular river. Slight viscous effects may be present in the models because particle Reynolds numbers are close to 70. Total bed load discharge was measured every fifteen minutes throughout each 60 hour run. In addition, 80 channel cross-sections were measured in each run to establish the average channel geometry. Total bed load transport rate correlates well with total discharge and total stream power, although at a given stream power bed load discharge is greater when braiding is less intense and the width/depth ratio is lower. Analysis using unit stream power and cross-section average bed shear stress reveals that the laboratory data conform to existing empirical bed load transport relationships. However, comparison with field data from gravel-bed rivers shows discrepancies that may be due to differences in bed material size gradation and bed sediment structure. At constant discharge, wide fluctuations in bed load discharge occur with some regularity. Periods range from 2 to 10 hours in the models, which is equivalent to several tens of hours in a prototype. The presence of these long-period fluctuations compounds the problems of field measurement of bed load in braided streams.     

Estimation of in-situ hydraulic diffusivity of rock masses

A method of estimating in-situ hydraulic diffusivity of rock masses by means of well-injection history and frequency of induced seismicity is presented. The method is based on the diffusion of injected fluid from a spherical cavity in a poroelastic half-space and the effective stress theory, as proposed byTerzaghi (1925, 1936) andHubbert andRubey (1959). Application of the method to two different regions, one in western New York and the other in Japan, resulted in estimated diffusivities of the order 10³ and 10⁴ cm²/sec, respectively. These values lie within the range of published estimates of in-situ diffusivity by other means, a summary of which is presented in tabular form. The calculated diffusivities suggest that the characteristic time of fluid diffusion is close to 0.1, rather than unity, as is sometimes assumed in the literature.     

The heat transfer in the region of the Mauna Kea (Hawaii)—constraints from borehole temperature measurements and coupled thermo-hydraulic modeling

The objectives of this paper are an understanding of the thermal and hydraulic field because of a negative temperature gradient and cold temperatures in the 1-km-deep borehole of the Hawaiian Scientific Drilling Project (HSDP), located near the coast line. The temperature pattern is attributed to a superposition of thermal and hydraulic processes. In the deeper borehole (HSDP-2, depth 3.1 km) detailed temperature monitoring was performed. Temperature measurements reveal two different thermal regimes. The upper part is characterised by cold temperatures and a negative temperature gradient similar to those observed in the shallow pilot borehole. Below 1100 m, increasing temperatures are observed. Different processes, such as topographically driven groundwater flow, ingress of salt water and conductive heat flow are investigated by numerical modeling. A pure conductive scenario fails to match the temperature measurements, implying that both borehole sections are overprinted by advective conditions. Coupled fluid and heat flow modeling with solute transport yield results that agree with observed temperatures. The results of these simulations suggest that meteoric water flow from the mountain range controls the thermal conditions in the upper part of the borehole. Below this level, the thermal regime is additionally affected by circulation of salt water from the nearby ocean. Each of these flow systems has been observed at other locations: topographically driven fresh water at locations with pronounced topography and ingress of salt water is typical for islands or coastal areas. At Hawaii, they coincide and influence each other, resulting in a salt water interface occurring at greater depth than expected.