Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern   总被引：2，自引：0，他引：2  

Huai-zhong Yu  Zheng-kang Shen  Yong-ge Wan  Qing-yong Zhu  Xiang-chu Yin   《Tectonophysics》2006,428(1-4):87-94

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.  相似文献   

The petroleum generation potential and effective oil window of humic coals related to coal composition and age   总被引：1，自引：0，他引：1  

Henrik I. Petersen   《International Journal of Coal Geology》2006,67(4):221-248

A worldwide data set of more than 500 humic coals from the major coal-forming geological periods has been used to analyse the evolution in the remaining (Hydrogen Index, HI) and total (Quality Index, QI) generation potentials with increasing thermal maturity and the ‘effective oil window’ (‘oil expulsion window’). All samples describe HI and QI bands that are broad at low maturities and that gradually narrow with increasing maturity. The oil generation potential is completely exhausted at a vitrinite reflectance of 2.0–2.2%R_o or T_max of 500–510 °C. The initial large variation in the generation potential is related to the original depositional conditions, particularly the degree of marine influence and the formation of hydrogen-enriched vitrinite, as suggested by increased sulphur and hydrogen contents. During initial thermal maturation the HI increases to a maximum value, HI_max. Similarly, QI increases to a maximum value, QI_max. This increase in HI and QI is related to the formation of an additional generation potential in the coal structure. The decline in QI with further maturation is indicating onset of initial oil expulsion, which precedes efficient expulsion. Liquid petroleum generation from humic coals is thus a complex, three-phase process: (i) onset of petroleum generation, (ii) petroleum build-up in the coal, and (iii) initial oil expulsion followed by efficient oil expulsion (corresponding to the effective oil window). Efficient oil expulsion is indicated by a decline in the Bitumen Index (BI) when plotted against vitrinite reflectance or T_max. This means that in humic coals the vitrinite reflectance or T_max values at which onset of petroleum generation occurs cannot be used to establish the start of the effective oil window. The start of the effective oil window occurs within the vitrinite reflectance range 0.85–1.05%R_o or T_max range 440–455 °C and the oil window extends to 1.5–2.0%R_o or 470–510 °C. For general use, an effective oil window is proposed to occur from 0.85 to 1.7%R_o or from 440 to 490 °C. Specific ranges for HI_max and the effective oil window can be defined for Cenozoic, Jurassic, Permian, and Carboniferous coals. Cenozoic coals reach the highest HI_max values (220–370 mg HC/g TOC), and for the most oil-prone Cenozoic coals the effective oil window may possibly range from 0.65 to 2.0%R_o or 430 to 510 °C. In contrast, the most oil-prone Jurassic, Permian and Carboniferous coals reach the expulsion threshold at a vitrinite reflectance of 0.85–0.9%R_o or T_max of 440–445 °C.  相似文献   

A novel strategy using biodegradable EDDS for the chemically enhanced phytoextraction of soils contaminated with heavy metals   总被引：1，自引：0，他引：1  

Chunling LUO Zhenguo SHEN Alan J.M. Baker Xiangdong LI 《中国地球化学学报》2006,25(B08):115-115

For the sake of cost and potential environmental risk, it is necessary to minimize the amount of chelates used in chemically-enhanced phytoextraction. In the present study, a biodegradable chelating agent, EDDS was added in a hot solution at 90℃ to the soil in which garland chrysanthemum （Chrysanthemum coronarium L.） and beans （Phaseolus vulgaris L., white bean） were growing. The application of hot chelate solutions was much more efficient than the application of normal chelate solutions （25℃） in improving the uptake of heavy metals by plants. When 1 mmol kg1 of EDDS as a hot solution was applied to soil, the concentrations ofCu, Zn and Cd and the total phytoextraction by the shoots of the two plant species exceeded or approximated those in the shoots of plants treated with 5 mmol kg^-1 of normal EDTA solution. The concentrations of metals in the shoots of beans were significantly correlated with the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the hot solution might play an important role in the process of chelate-enhanced metal uptake. The soil leaching study demonstrated that decreasing the dosage of chelate resulted in decreased concentrations of soluble metals in soils. On the 28th day following the application of chelate, the concentrations of soluble metals in the EDDS treated soil were not significantly different from the concentrations in the control soil to which chelates had not been applied.  相似文献   

Early Jurassic rift structures associated with the Soapaga and Boyacá faults of the Eastern Cordillera, Colombia: Sedimentological inferences and regional implications     

Andreas Kammer  Javier Snchez 《Journal of South American Earth Sciences》2006,21(4):412

The NW-trending Bucaramanga fault links, at its southern termination, with the Soapaga and Boyacá faults, which by their NW trend define an ample horsetail structure. As a result of their Neogene reactivation as reverse faults, they bound fault-related anticlines that expose the sedimentary fill of two Early Jurassic rift basins. These sediments exhibit the wedge-like geometry of rift fills related to west-facing normal faults. Their structural setting was controlled further by segmentation of the bounding faults at approximately 10 km intervals, in which each segment is separated by a transverse basement high. Isopach contours and different facies associations suggest these transverse anticlines may have separated depocenters of their adjacent subbasins, which were shaped by a slightly different subsidence history and thereby decoupled. The basin fill of the relatively narrow basin associated with the Soapaga fault is dominated by fanglomeratic successions organized in two coarsening-upward cycles. In the larger basin linked to the Boyacá fault, the sedimentary fill consists of two coarsening-upward sequences that, when fully developed, vary from floodplain to alluvial fan deposits. These Early Jurassic rift fills temporally constrain the evolution of the Bucaramanga fault, which accommodated right-lateral displacement during the early Mesozoic rift event.  相似文献   

The seismic hazard assessment of the Dead Sea rift, Jordan   总被引：1，自引：0，他引：1  

Abdallah S. Al-Zoubi  Z.S.H. Abu-Hamatteh  Amrat Abdealkaderer 《Journal of African Earth Sciences》2006,45(4-5):489-501

The Dead Sea fault system and its branching faults represent one of the most tectonically active regions in the Middle East. The aim of this study is to highlight the degree of hazards related to the earthquake activities associated with the Dead Sea rift, in terms of speculating the possible future earthquakes. The present investigation mainly is based on available data and vertical crustal modeling of Jordan and the Dead Sea model for the Dead Sea basin with particular emphasis of the recent earthquake activities, which occurred on December 31st, 2003 (Mc = 3.7), February 11th, 2004 (strongest Mc = 4.9 R), and March 15th, 2004 (Mc = 4). The present research examines the location of the strong events and correlates them with the various tectonic elements in the area. The source mechanism of the main shock and the aftershock events is also examined. The analyses were based on the available short period seismogram data, which was recorded at the Natural Resources Authority of Jordan, Seismological Observatory. The seismic energy appears to have migrated from the south to the north during the period from December 31st up to March 12th, where the released seismic energy showed a migration character to the southern block of the eastern side of the Dead Sea, which led the seismic event to occur on March 15th.  相似文献   

Testing earthquake prediction methods: «The West Pacific short-term forecast of earthquakes with magnitude MwHRV ≥ 5.8»     

V.G. Kossobokov   《Tectonophysics》2006,413(1-2):25

Analyzing the tables and probability maps posted by Yan Y. Kagan and David D. Jackson in April 2002–September 2004 at http://scec.ess.ucla.edu/~ykagan/predictions_index.html and the catalog of earthquakes for the same period, the conclusion is drawn that the underlying method could be used for prediction of aftershocks, while it does not outscore random guessing when main shocks are considered.  相似文献   

A laboratory experiment to monitor the contact state of a fault by transmission waves   总被引：1，自引：0，他引：1  

Naoto Yoshioka  Koji Iwasa 《Tectonophysics》2006,413(3-4):221-238

We performed a series of laboratory experiments in which elastic waves were transmitted across a simulated fault. Two types of experiments were carried out: (1) Normal Stress Holding Test (NSHT): normal stress was kept constant for about 3 h without shear stress and transmission waves were observed. (2) Shear Stress Increasing Test (SSIT): shear stress was gradually increased until a stick-slip event occurred. Transmission waves were continuously observed throughout the process of stress accumulation. We focused on the change in transmission waves during the application of shear stress and especially during precursory slips.It was found in NSHT that the amplitude of transmission waves linearly increased with the logarithm of stationary contact time. The increase amounted to a few percent after about 3 h. Creep at asperity contacts is responsible for this phenomenon. From a theoretical consideration, it was concluded that the real contact area increased with the logarithm of stationary contact time.We observed in SSIT a significant increase in wave amplitude with shear stress application. This phenomenon cannot be attributed to the time effect observed in NSHT. Instead, it can be explained by the mechanism of “junction growth” proposed by Tabor. Junction growth yields an increase in real contact area. It is required for junction growth to occur that the material in contact is already plastic under a purely normal loading condition. A computer simulation confirmed that this requirement was satisfied in our experiments. We also found that the rate at which the amplitude increased was slightly reduced prior to a stick-slip event. The onset time of the reduction well coincides with the onset of precursory slip. The cause of the reduction is attributed to the reset of stationary contact time due to displacement. This interpretation is supported by the result of NSHT. Taking the time of stationary contact in SSIT into account, we may expect the change in wave amplitude to be, at most, only a few percent. The observed slight reduction in increasing rate is, in this sense, reasonable. The static stiffness of the fault also decreases with precursory slip. It was also found that low frequency waves are a better indicator of precursory slip than high frequency waves. This might suggest that low frequency waves with longer wavelength are a better indicator of average behavior of faults. The problem, however, merits a further investigation. The shifts in phase were also found to be a good indicator of the change in contact state of the fault. The changes in both amplitude and phase of transmission waves are unifyingly understood through the theory of transmission coefficient presented by Pyrak-Nolte et al. Rough surfaces have a tendency to give larger stick-slips than smooth surfaces. The amount of precursory slip is larger for rough surfaces than for smooth surfaces. Although it was confirmed by a computer simulation that rough surfaces have larger contact diameters than smooth surfaces, the rigorous relationship between the surface roughness (contact diameter) and the amount of precursory slips was not established.  相似文献   

A way to synchronize models with seismic faults for earthquake forecasting: Insights from a simple stochastic model     

lvaro Gonzlez  Miguel Vzquez-Prada  Javier B. Gmez  Amalio F. Pacheco 《Tectonophysics》2006,424(3-4):319

Numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks. Their final goal would be to forecast future large earthquakes. In order to use them for this task, it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates (just as, for example, meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them). However, lithospheric dynamics is largely unobservable: important parameters cannot (or can rarely) be measured in Nature. Earthquakes, though, provide indirect but measurable clues of the stress and strain status in the lithosphere, which should be helpful for the synchronization of the models.The rupture area is one of the measurable parameters of earthquakes. Here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes. Our purpose here is to forecast synthetic earthquakes in a simple but stochastic (random) fault model. By imposing the rupture area of the synthetic earthquakes of this model on other models, the latter become partially synchronized with the first one. We use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model. This forecasting strategy outperforms others that only take into account the earthquake series. Our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults. This hypothesis could be tested in the future with more detailed models and actual seismic data.  相似文献   

Great earthquakes of variable magnitude at the Cascadia subduction zone   总被引：1，自引：0，他引：1  

Alan R. Nelson  Harvey M. Kelsey 《Quaternary Research》2006,65(3):354-365

Comparison of histories of great earthquakes and accompanying tsunamis at eight coastal sites suggests plate-boundary ruptures of varying length, implying great earthquakes of variable magnitude at the Cascadia subduction zone. Inference of rupture length relies on degree of overlap on radiocarbon age ranges for earthquakes and tsunamis, and relative amounts of coseismic subsidence and heights of tsunamis. Written records of a tsunami in Japan provide the most conclusive evidence for rupture of much of the plate boundary during the earthquake of 26 January 1700. Cascadia stratigraphic evidence dating from about 1600 cal yr B.P., similar to that for the 1700 earthquake, implies a similarly long rupture with substantial subsidence and a high tsunami. Correlations are consistent with other long ruptures about 1350 cal yr B.P., 2500 cal yr B.P., 3400 cal yr B.P., 3800 cal yr B.P., 4400 cal yr B.P., and 4900 cal yr B.P. A rupture about 700-1100 cal yr B.P. was limited to the northern and central parts of the subduction zone, and a northern rupture about 2900 cal yr B.P. may have been similarly limited. Times of probable short ruptures in southern Cascadia include about 1100 cal yr B.P., 1700 cal yr B.P., 3200 cal yr B.P., 4200 cal yr B.P., 4600 cal yr B.P., and 4700 cal yr B.P. Rupture patterns suggest that the plate boundary in northern Cascadia usually breaks in long ruptures during the greatest earthquakes. Ruptures in southernmost Cascadia vary in length and recurrence intervals more than ruptures in northern Cascadia.  相似文献   

Origin and three-dimensional fluorescence spectrum of the chromophoric dissolved organic matter in Yangtze estuary, East China     

Fan YANG Qinghui HUANG Jianhua LI Xiaomin ZHU 《中国地球化学学报》2006,25(B08):262-262

Dissolved organic matter （DOM） is an important chemical component in natural water. Chromophoric dissolved organic matter （CDOM）, a fraction of optical properties, plays art important role in the biogeochemical cycle of nutrients in aquatic environment. People realized that DOM cycle is crucial in the global carbon and nitrogen flux, and also is inherently related to nutrients and trace metal elements. Therefore, CDOM was concerned by scientists in global oceanography and limnology fields. Water samples were collected from three sections （North Channel, South Channel and Zhuyuan） of the Yangtze （Changjiang River） estuary in March 2006 Three-dimensional excitation emission matrix （3-DEEM） fluorescence spectra were analyzed for those filtrates through Whatman GF/F filters. Dissolved organic carbon （DOC） was also measured by TOC analyzer. The tidal variety was also taken into account. The 3-D EEM fluorescence scans suggested the fluorescence characteristics of humic acid （Ex=332-344 nm, Em=439-451 nm） and fulvic acid （Ex=250-254 nm, Em=472-478 nm） were obvious, and the fluorescence group of protein-like and tyrosine （Ex=230 nm, Em=283 nm） was also found. They are mainly composed of CDOM in the Yangtze estuary. Further data analysis, especially the fluorescence index （f 450/500）, showed that terrestrial signal was rather strong （1.41-1.65） in the surface water, however, some terrestrial CDOM signals of bottom water showed excursions （1.28-1.39）. On the other hand, anthropogenic sign was impressed in the waters of Zhuyuan, which is one of the main drain outlets of Shanghai Metropolis. DOC concentrations ranged from 2.2 mg/L to 3.4 mg/L in Zhuyuan and South Channel, and from 2.0 mg/L to 2.4 mg/L in North Channel. The tide effect played a role in the composition of the CDOM measured by 3-D fluorescence scan technology.  相似文献