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171.
Aftershock sequence simulations using synthetic earthquakes and rate-state seismicity formulation
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Heming Xu Yifeng Cui James H. Dieterich Keith Richards-Dinger Efecan Poyraz Dong Ju Choi 《地震科学(英文版)》2014,27(4):401-410
We use an efficient earthquake simulator that incorporates rate-state constitutive properties and uses boundary element method to discretize the fault surfaces, to generate the synthetic earthquakes in the fault system. Rate-and-state seismicity equation is subsequently employed to calculate the seismicity rate in a region of interest using the Coulomb stress transfer from the main shocks in the fault system. The Coulomb stress transfer is obtained by resolving the induced stresses due to the fault patch slips onto the optimal-oriented fault planes. The example results show that immediately after a main shock the aftershocks are concentrated in the vicinity of the rupture area due to positive stress transfers and then disperse away into the surrounding region toward the background rate distribution. The number of aftershocks near the rupture region is found to decay with time as Omori aftershock decay law predicts. The example results demonstrate that the rate-and-state fault system earthquake simulator and the seismicity equations based on the rate-state friction nucleation of earthquake are well posited to characterize the aftershock distribution in regional assessments of earthquake probabilities. 相似文献
172.
Daniel Leduc Ashley A. Rowden Conrad A. Pilditch Elizabeth W. Maas P. Keith Probert 《Marine Ecology》2013,34(3):334-344
Studying the diversity‐ecosystem function relationship in the deep sea is of primary importance in the face of biodiversity loss and for our understanding of how the deep sea functions. Results from the first study of diversity‐ecosystem function relationships in the deep sea (Danovaro et al. 2008; Current Biology, 18, 1–8) are unexpected and show an exponential relationship between deep‐sea nematode diversity and ecosystem function and efficiency, although this relationship appears largely restricted to relatively low diversities [ES(51) <25]. Here, we investigate the relationship between nematode diversity and several independent measures/proxies of ecosystem function (sediment community oxygen consumption, bacterial biomass, bacterial extracellular enzyme activity) and efficiency (ratio of bacterial/nematode carbon to organic C content of the sediment) on the New Zealand continental slope. Nematode diversity at our study sites was relatively high [ES(51) = 30–42], and there was no relationship between species/functional diversity and ecosystem function/efficiency after accounting for the effects of water depth and food availability. Our results are consistent with a breakdown of the exponential diversity‐function relationship at high levels of diversity, which may be due to increased competition or greater functional redundancy. Future studies need to take into account as many environmental factors and as wide a range of diversities as possible to provide further insights into the diversity‐ecosystem function relationship in the largest ecosystem on Earth. 相似文献
173.
Wither A Bamber R Colclough S Dyer K Elliott M Holmes P Jenner H Taylor C Turnpenny A 《Marine pollution bulletin》2012,64(8):1564-1579
The construction of a new generation of coastal power stations in the UK and other western European countries has highlighted the absence of robust standards for thermal discharges to transitional and coastal waters. The proposed discharge volumes are greater than hitherto, yet there has been little independent critical examination of their potential impact, whilst much of the existing guidance has been adapted from freshwater practice. This review considers the available knowledge on the tolerance and behaviour of fish and other marine biota to heated effluents. Appropriate ways are suggested of grouping fish species to reflect their sensitivity to thermal effects. The plethora of existing standards are considered and their validity assessed in a framework of predicted seawater temperature rise. Those species or groups of organisms most likely to be affected are identified and finally specific recommendations for thermal standards consistent with long term sustainability are proposed. 相似文献
174.
The water vapour continuum is characterised by absorption that varies smoothly with wavelength, from the visible to the microwave. It is present within the rotational and vibrational–rotational bands of water vapour, which consist of large numbers of narrow spectral lines, and in the many ‘windows’ between these bands. The continuum absorption in the window regions is of particular importance for the Earth’s radiation budget and for remote-sensing techniques that exploit these windows. Historically, most attention has focused on the 8–12?μm (mid-infrared) atmospheric window, where the continuum is relatively well-characterised, but there have been many fewer measurements within bands and in other window regions. In addition, the causes of the continuum remain a subject of controversy. This paper provides a brief historical overview of the development of understanding of the continuum and then reviews recent developments, with a focus on the near-infrared spectral region. Recent laboratory measurements in near-infrared windows, which reveal absorption typically an order of magnitude stronger than in widely used continuum models, are shown to have important consequences for remote-sensing techniques that use these windows for retrieving cloud properties. 相似文献
175.
We employ a computationally efficient fault system earthquake simulator, RSQSim, to explore effects of earthquake nucleation and fault system geometry on earthquake occurrence. The simulations incorporate rate- and state-dependent friction, high-resolution representations of fault systems, and quasi-dynamic rupture propagation. Faults are represented as continuous planar surfaces, surfaces with a random fractal roughness, and discontinuous fractally segmented faults. Simulated earthquake catalogs have up to 106 earthquakes that span a magnitude range from ~M4.5 to M8. The seismicity has strong temporal and spatial clustering in the form of foreshocks and aftershocks and occasional large-earthquake pairs. Fault system geometry plays the primary role in establishing the characteristics of stress evolution that control earthquake recurrence statistics. Empirical density distributions of earthquake recurrence times at a specific point on a fault depend strongly on magnitude and take a variety of complex forms that change with position within the fault system. Because fault system geometry is an observable that greatly impacts recurrence statistics, we propose using fault system earthquake simulators to define the empirical probability density distributions for use in regional assessments of earthquake probabilities. 相似文献
176.
Keith Porter 《地震工程与结构动力学》2016,45(5):819-833
Second‐generation performance‐based earthquake engineering (PBEE‐2) requires a library of component fragility functions to estimate probabilistic damage to a wide variety of building components. The present work draws on a large body of (mostly) post‐earthquake reconnaissance and (some) post‐earthquake survey observations of traction elevators to create fragility functions useful in PBEE‐2. Two surveys provide detailed observations of 115 representative elevators at 12 hospitals shaken in the 1989 Loma Prieta and 1994 Northridge earthquakes and selected without regard to or foreknowledge of damage. Of these, 55 failed and 60 did not. Approximately half were installed after an important code change of 1972, so one can distinguish the performance of pre‐1973 and post‐1973 elevator construction. They experienced a range of strong motion: 22 with peak ground acceleration (PGA) < 0.25 g, 93 with 0.25 g < PGA < 0.85 g. The hospitals had elevator failure rates as low as 0% and as high as 100%. A third survey describes damage qualitatively for six sites with PGA ≤ 0.25 and per‐site failure rates of 0% to perhaps 30%. Fragility functions are offered where the damage state is the loss of functionality of the elevator. The elevators in these surveys exhibit a median capacity of PGA ≈ 0.35 g with a logarithmic standard deviation of 0.40. Capacity is modestly sensitive to whether the elevator was installed before or after 1973. Using building‐specific intensity measures such as Sa(T1) does not improve the fragility functions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
177.
Xiuyu Liang You-Kuan Zhang Keith Schilling 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(1):1-8
Spatiotemporal variations of groundwater level due to a white noise recharge time series and a random transmissivity field in a bounded unconfined aquifer was studied. The analytical solutions for the variance and covariance of groundwater level were derived with non-stationary spectral analyses and superposition principle. It was found that the fluctuations of groundwater level are spatially non-stationary due to a fixed head boundary condition and temporal non-stationary at early time but gradually became stationary as time progresses due to effect of the initial condition. The variation in groundwater level is mainly caused by the random source/sink in the case of temporally random recharge and spatially random transmissivity. The effect of heterogeneity is to increase the variation of groundwater level and the maximum effect occurs close to the constant head boundary because of the linear mean hydraulic gradient. The heterogeneity also enhances the correlation of groundwater level, especially at large time intervals and small spatial distances. 相似文献
178.
A vertical profile of maximum horizontal principal stress, SHmax, orientation to 5 km depth was obtained beneath the Swiss
city of Basel from observations of wellbore failure derived from ultrasonic televiewer images obtained in two 1 km distant
near-vertical boreholes: a 2755 m exploration well (OT2) imaged from 2550 m to 2753 m across the granitic basement-sediment
interface at 2649 m; and a 5 km deep borehole (BS1) imaged entirely within the granite from 2569 m to 4992 m. Stress-related
wellbore failure in the form of breakouts or drilling-induced tension fractures (DITFs) occurs throughout the depth range
of the logs with breakouts predominant. Within the granite, DITFs are intermittently present, and breakouts more or less continuously
present over all but the uppermost 100 m where they are sparse. The mean SHmax orientations from DITFs is 151 ± 13° whereas
breakouts yield 143 ± 14°, the combined value weighted for frequency of occurrence being N144°E ± 14°. No marked depth dependence
in mean SHmax orientation averaged over several hundred meters depth intervals is evident. This mean SHmax orientation for
the granite is consistent with the results of the inversion of populations of focal mechanism solutions of earthquakes occurring
between depths of 10–15 km within regions immediately to the north and south of Basel, and with the T-axis of events occurring
within the reservoir (Deichmann and Ernst, this volume). DITFs and breakouts identified in OT2 above and below the sediment-basement
interface suggest that a change in SHmax orientation to N115°E ± 12° within the Rotliegendes sandstone occurs near its interface
with the basement. The origin of the 20–30° change is uncertain, as is its lateral extent. The logs do not extend higher than
80 m above the interface, and so the data do not define whether a further change in stress orientation occurs at the evaporites.
Near-surface measurements taken within 50 km of Basel suggest a mean orientation of N–S, albeit with large variability, as
do the orientation of hydrofractures at depths up to 850 m within and above the evaporite layers and an active salt diapir,
also within 50 km of Basel. Thus, the available evidence supports the notion that the orientation of SHmax above the evaporites
is on average more N–S oriented and thus differs from the NW–SE inferred for the basement from the BS1/OS2 wellbore failure
data and the earthquake data. Changes in stress orientation with depth can have significant practical consequences for the
development of an EGS reservoir, and serve to emphasise the importance of obtaining estimates from within the target rock
mass. 相似文献
179.
Keith E. Schilling 《Hydrogeology Journal》2009,17(2):397-407
Groundwater recharge is an important component to hydrologic studies but is known to vary considerably across the landscape. The purpose of this study was to examine 4 years of water-level behavior in a transect of four water-table wells installed at Walnut Creek, Iowa, USA to evaluate how groundwater recharge varied along a topographic gradient. The amount of daily water-table rise (WTR) in the wells was summed at monthly and annual scales and estimates of specific yield (Sy) were used to convert the WTR to recharge. At the floodplain site, Sy was estimated from the ratio of WTR to total rainfall and in the uplands was based on the ratio of baseflow to WTR. In the floodplain, where the water table is shallow, recharge occurred throughout the year whenever precipitation occurred. In upland areas where the water table was deeper, WTR occurred in a stepped fashion and varied by season. Results indicated that the greatest amount of water-table rise over the 4-year period was observed in the floodplain (379 mm), followed by the upland (211 mm) and sideslopes (122 mm). Incorporating spatial variability in recharge in a watershed will improve groundwater resource evaluation and flow and transport modeling. 相似文献
180.
Darkness on the Edge of Town: Mapping Urban and Peri-Urban Australia Using Nighttime Satellite Imagery 总被引:1,自引:1,他引:0
Paul C. Sutton Andrew R. Goetz Stephen Fildes Clive Forster Tilottama Ghosh 《The Professional geographer》2013,65(1):119-133
This article explores the use of nighttime satellite imagery for mapping urban and peri-urban areas of Australia. A population-weighted measure of urban sprawl is used to characterize relative levels of sprawl for Australia's urban areas. In addition, the expansive areas of low light surrounding most major metropolitan areas are used to map the urban–bush interface of exurban land use. Our findings suggest that 82 percent of the Australian population lives in urban areas, 15 percent live in peri-urban or exurban areas, and 3 percent live in rural areas. This represents a significantly more concentrated human settlement pattern than presently exists in the United States. 相似文献