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1.
在地震的孕育、发生到发展的过程中，可能会出现多项地下流体观测量不同程度的前兆异常变化，这些异常变化是复杂多样、模糊不清的。引入模糊识别法对一定区域和一定时间段的地下流体观测数据进行了分析和处理，表明模糊识别法可较好地识别和分辨出地下流体前兆的地震异常。 相似文献
2.
Based on tide gauge observations spanning almost 200 years, homogeneous time series of the mean relative sea level were derived for nine sites at the southern coast of the Baltic Sea. Our regionally concentrated data were complemented by long-term relative sea-level records retrieved from the data base of the Permanent Service for Mean Sea Level (PSMSL). From these records relative sea-level change rates were derived at 51 tide gauge stations for the period between 1908 and 2007. A minimum observation time of 60 years is required for the determination of reliable sea-level rates. At present, no anthropogenic acceleration in sea-level rise is detected in the tide gauge observations in the southern Baltic. The spatial variation of the relative sea-level rates reflects the fingerprint of GIA-induced crustal uplift. Time series of extreme sea levels were also inferred from the tide gauge records. They were complemented by water level information from historic storm surge marks preserved along the German Baltic coast. Based on this combined dataset the incidence and spatial variation of extreme sea levels induced by storm surges were analysed yielding important information for hazard assessments. Permanent GPS observations were used to determine recent crustal deformation rates for 44 stations in the Baltic Sea region. The GPS derived height change rates were applied to reduce the relative sea-level changes observed by tide gauges yielding an estimate for the eustatic sea-level change. For 13 tide gauge-GPS colocation sites a mean eustatic sea-level trend of 1.3 mm/a was derived for the last 100 years. 相似文献
3.
河北省数字地电场数据分析 总被引：13，自引：0，他引：13
通过分析总结河北省数字地电场的正常场和异常信息，发现正常记录除了显示日变周期外，还记录到了半日和三分之一日周期，比较长的周期还有半月周期等；干扰信息主要与电极极化及磁暴等有关，大磁暴干扰一般会出现高频信号，破坏正常日变形态，其主要表现为多台同步等幅信号；对台站的电场方向性研究发现，在正常时段电场记录方向性显著，而磁暴记录期内方向性较差，显示外空异常源方向比较复杂。最后对一些可能与地震有关的异常现象进行了分析探讨。我们认为，目前的多极距地电场观测对排除干扰及异常识别带来很大方便，但共用电极的观测方式为异常识别增加了障碍。 相似文献
4.
V. G. Getmanov A. D. Gvishiani K. Stroker G. Mungov 《Izvestiya Physics of the Solid Earth》2012,48(9-10):671-679
The problem of recognizing the time intervals with Rayleigh-wave disturbances in the signals from the depth pressure transducers of the ocean-bottom seismic stations (OBS) is considered in the context of the tsunami-warning problem. A new recognition algorithm, which makes use of the frequency-time distribution functions (FTD) of the OBS signals, and the decision-making procedure based on the comparison of the calculated and reference FTD functions are developed. The results of recognizing the Rayleigh wave disturbances in the OBS signals are presented. The suggested approach can serve as an efficient means for solving the problems of recognition and classification of the disturbances in the time series of various geophysical observations. 相似文献
5.
Late Weichselian relative sea-level changes and ice sheet history in southeast Greenland 总被引：1，自引：0，他引：1
Antony J. Long David H. Roberts Matthew J.R. Simpson Sue Dawson Glenn A. Milne Philippe Huybrechts 《Earth and Planetary Science Letters》2008,272(1-2):8-18
Relative sea-level (RSL) observations from the margins of the Greenland Ice Sheet (GIS) provide information regarding the timing and rate of deglaciation and constraints on geophysical models of ice sheet evolution. In this paper we present the first RSL record for the southeast sector of the GIS based on field observations completed close to Ammassalik. The local marine limit is c. 69 m above sea-level (asl) and is dated to c. 11 k cal. yrs BP (thousand calibrated years before present) and is a minimum date for ice free conditions at the study site. RSL fell to c. 24 m asl by 9.5 k cal. yrs BP and continued to fall at a decreasing rate to reach close to present by 6.5 k cal. yrs BP. Our chronology agrees with radiocarbon dates from offshore cores that indicate ice free conditions on the adjacent mid-shelf by 15 k cal. yrs BP. We compare the new RSL data with predictions generated using two recently published glaciological models of the GIS that differ in the amount and timing of ice loading and unloading over our study area. These two GIS models are coupled to the same Earth viscosity model and background (global) ice model to aid in the data-model comparison. Neither model provides a close fit to the RSL observations. Based on a preliminary sensitivity study using a suite of Earth viscosity models, we conclude that the poor data-model fit is most likely due to an underestimate of the local ice unloading. An improved fit could be achieved by delaying the retreat of a thicker ice sheet across the continental shelf. A thick ice sheet extending well onto the continental shelf is in agreement with other recent observations elsewhere in east and south Greenland. 相似文献
6.
A. Carret J. A. Johannessen O. B. Andersen M. Ablain P. Prandi A. Blazquez A. Cazenave 《Surveys in Geophysics》2017,38(1):251-275
Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite altimetry era. We investigate the closure of the sea-level budget since 2002 using two altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns. 相似文献
7.
Andreas Richter Søren Rysgaard Reinhard Dietrich John Mortensen Dorthe Petersen 《Ocean Dynamics》2011,61(1):39-49
Based on pressure tide-gauge observations, sea-level records are derived for ten sites along the coast of West Greenland.
The ocean tidal signal is extracted by a harmonic tidal analysis. The accuracy of the determined tidal constants is discussed
in detail. The tides account for 85% of the observed sea-level standard deviation. The tide gauge records reveal significant
shallow-water tidal effects, in particular compound and overtide amplitudes reaching 5 cm. The propagation of the tidal waves
into the fjords depends strongly on local conditions and is in some cases accompanied by an amplification of the tidal amplitudes.
The observed tidal signals are compared to the predictions of the global ocean tide model FES2004. At the outer coast, a good
agreement is found. Inside the fjords, however, the model performs worse and tide gauge observations may still be indispensable
when accurate tidal signals are required. 相似文献
8.
Giorgio Spada 《Surveys in Geophysics》2017,38(1):153-185
Glacial isostatic adjustment (GIA) encompasses a suite of geophysical phenomena accompanying the waxing and waning of continental-scale ice sheets. These involve the solid Earth, the oceans and the cryosphere both on short (decade to century) and on long (millennia) timescales. In the framework of contemporary sea-level change, the role of GIA is particular. In fact, among the processes significantly contributing to contemporary sea-level change, GIA is the only one for which deformational, gravitational and rotational effects are simultaneously operating, and for which the rheology of the solid Earth is essential. Here, I review the basic elements of the GIA theory, emphasizing the connections with current sea-level changes observed by tide gauges and altimetry. This purpose is met discussing the nature of the “sea-level equation” (SLE), which represents the basis for modeling the sea-level variations of glacial isostatic origin, also giving access to a full set of geodetic variations associated with GIA. Here, the SLE is employed to characterize the remarkable geographical variability of the GIA-induced sea-level variations, which are often expressed in terms of “fingerprints”. Using harmonic analysis, the spatial variability of the GIA fingerprints is compared to that of other components of contemporary sea-level change. In closing, some attention is devoted to the importance of the “GIA corrections” in the context of modern sea-level observations, based on tide gauges or satellite altimeters. 相似文献
9.
IntroductionGenerallyspeaking,thedataofprecursorymonitoringwhichmightbeassociatedwiththepreparationofthefutureearthquakes,couldberepresentedbyatimeseries.There,however,wouldbenotonlyanomalouschangesassociatedwiththeearthquakeoccurrences,butalsosomechangeswhichwouldberelatedtosourcesotherthantheearthquakepreparation,eitherknownorunknowntotheinvestigatorsandbecalledas(thechangesfromnon-earthquakeeffects(,inthetimeseries,inpractice,tillnow.ItistosaythatthetimeseriesF(t)showingthetemporalchangesof… 相似文献
10.
The vulnerability to short-term and long-term sea-level rises is particularly high in subsiding deltaic areas, especially in microtidal seas, when surges (the differences between the observed sea heights and the simultaneous astronomical tide) are frequent. At the Grau-de-la-Dent tide-gauge in the Camargue (Rhone delta, France), daily sea-level records are available since 1905. Hourly tide data spanning the period 1979–1995 were obtained through the digitisation of the original paper records: the local harmonic constants and the surges for the whole 20th century have been computed from these hourly observations. It appears that the annual maximum observed sea-level height increases by 4 mm/yr at a rate that is two times faster than the average observed relative sea level. The increasing trend of the annual maximum positive sea surges (+1.9 mm/yr), which is equal to the average relative sea-level rise, is thus responsible for this difference. The most important meteorological factor associated with local sea-surge occurrences is wind blowing from 100° to 120° sectors, which tends to push the water toward the coasts. Since 1961, the frequency and the speed of wind from this sector increased, although with some variability, thus contributing in part to the increase in the frequency and intensity of the surges. Due to the changing hydrodynamics phenomenon in the Camargue, a positive feedback mechanism between extreme marine events and shoreline regression is another factor to explain the sea-surge rise over the long term. The increase in sea-surge frequency and height during the last century is especially of concern in the deltaic area if the near-future global sea-level rise predicted by climate models is also taken into account. 相似文献
11.
Yu. F. Moroz 《Izvestiya Physics of the Solid Earth》2008,44(11):933-940
The paper presents results of observations of the electromagnetic field conducted on the ice and coast of Lake Baikal. The horizontal and vertical components of the electric field contain anomalous disturbances coinciding in time with earthquakes and with the origination of a crevice in the ice cover of the lake. A possible origin of the anomalous disturbances is considered. 相似文献
12.
During the detailed excavations of ancient Caesarea, Israel, East Mediterranean, 64 coastal water wells have been examined that date from the early Roman period (with the oldest occurring in the 1st century AD), up to the end of the Crusader period (mid-13th century AD). The depths of these coastal water wells establish the position of the ancient water table and therefore the position of sea level for the first century AD up to 1300 AD. The connection between the coastal water table and changes in sea level has been established from modern observations in several wells on time scales of days and months and this is used to reconstruct sea level during historical time. The results indicate that during the Byzantine period, sea level at Caesarea was higher by about 30 cm than today. The Late Moslem and Crusader data shows greater fluctuations but the data sets are also much smaller than for the earlier periods. The consistency of the data indicates that the near-coastal well data from Caesarea provides a reliable indicator of sea-level change, with an accuracy of about 10-15 cm. These results are consistent with observations for earlier periods and, with comparisons to model-predicted glacio-hydro isostatic sea-level change, indicate that ocean volumes have been constant for much of the past 2000 years. The well data is also consistent with an absence of significant vertical tectonic movement of the coast at Caesarea over about 2000 years. 相似文献
13.
Geochemical changes across the Ordovician-Silurian transition on the Yangtze Platform,South China 总被引：1，自引：0，他引：1
The trace element and rare earth element (REE) variations across the Ordovician-Silurian succession are presented from two
outcrop sections on the Yangtze Platform: the Nanbazi section, Guizhou Province, deposited in a shallow platform interior
setting, and the Wangjiawan section, Hubei Province, deposited in a deeper basinal environment. Geochemical analysis of closely
spaced samples through three intervals, the Wufeng, Guanyinqiao and Longmaxi, revealed vast palaeoceanographic changes. Some
geochemical proxies, including Th/U, Ni/Co, V/Cr, and V/(V+Ni) ratios, together with sedimentary facies and biotic data, indicate
that an anoxic condition on the most of the Yangtze Platform during the Wufeng and Longmaxi intervals, but an oxic condition
during the Guanyinqiao time. The shift of the anoxic to the oxic environment during the Guanyinqiao time coincided with a
global sea-level lowstand, in parallel with the global glaciation. The Longmaxian anoxic environment was a result of a global
sea-level rise, which may be synchronized with a mainly catastrophic event in the latest Ordovician. Although the two sections
generally show similar variation patterns of trace and REE concentrations and some element ratios, a minor difference occurs
between the Wangjiawan and Nanbazi sections, likely reflecting a difference in depositional setting during the accumulation.
Such an oceanic oxygen-level variation may add a useful constraint to the current arguments on the cause and consequence of
the latest Ordovician mass extinction.
Supported by National Basic Research Program of China (Grant No. 2005CB422101) 相似文献
14.
Mapping the mesoscale surface velocity stream function by combining estimates of surface height from satellite altimetry
and surface currents from sequential infrared (sea-surface temperature) imagery using optimal interpolation is described.
Surface currents are computed from infrared images by the method of maximum cross-correlations (MCC) and are combined with
altimeter sea-level anomaly data from the TOPEX/Poseidon and ERS satellites. The analysis method was applied to 6 years of
data from the East Australian Current region. The covariance of velocity and sea-level data is consistent with the statistical
assumptions of homogeneous, isotropic turbulence, with typical length scales of order 220 km and time scales of 10 days in
this region. Augmenting the analysis of altimeter data with MCC velocity observations improves the resolution of the surface
currents, especially near the Australian coast, and demonstrates that the two data sources provide consistent and complementary
observations of the surface mesoscale circulation. The volume of MCC data is comparable to that from a satellite altimeter,
but with a more variable distribution of spatial and temporal resolution. In concert with altimetry, satellite radiometer
velocimetry represents a technique useful for retrospective analysis of currents from high-resolution satellite radiometer
data-sets.
Received: 3 July 2001 / Accepted: 16 November 2001 相似文献
15.
The strong ground motion produced by the 17 October, 1989 Loma Prieta earthquake in northern California was recorded at over 100 stations. Accelerograms were generated at sites with significantly different geology, including land fill and soft sedimentary soil sites. In this study, the attenuation characteristics of the peak vertical and horizontal ground accelerations are studied for freefield recording conditions within 100 km of the source by the application of a non-linear multi-regression procedure. Two sets of attenuation models for weighted and unweighted observations are compared with those reported by other investigators for this earthquake and for regional and worldwide data. The peak ground acceleration (PGA) observations for this earthquake exceed previous predictions of standard attenuation models, particularly beyond 30 km (approximately 60 percent at 50 km). Higher attenuation of the vertical component compared to the horizontal is confirmed. The regression considers site geology as an independent parameter. Soil sites display as much as 23 per cent amplification relative to rock sites for horizontal PGA and as much as 40 per cent for vertical PGA. Amplification of the ground motion at sites characterized by soft soil geology is examined by comparing the recorded PGA with the corresponding prediction at sites underlain by stiff soil. Eight of ten of the soft soil sites display significant amplification relative to stiff soil sites (as much as 300 per cent for horizontal and 200 per cent for vertical components). Particular attention is paid to the so-called anomalous observations at distances beyond 50 km. The anomalous observations between 50 and 80 km may be attributed to various factors such as geology, basic geometry, azimuthal dependence, source mechanism and normal scatter of observations. 相似文献
16.
《Continental Shelf Research》1995,15(8):981-1014
Low frequency sea-level variations and associated geostrophic currents in the central Great Barrier Reef (GBR) region near Townsville are studied using optimally-lagged multivariate regression. The analyses show that pressure-adjusted coastal sea levels and mid-shelf geostrophic currents are influenced predominantly by local along-shelf wind stress at the weather time-scale, and by climatic variables, such as atmospheric pressure and temperature, at seasonal and inter-annual time-scales. These forcing variables can specify sea levels over annual and inter-annual time-scales with a forecasting skill of 0.53 and 0.22, respectively (where 1.0 is perfect skill). Associated along-shelf geostrophic currents can be forecast with a skill of 0.57 over an annual time scale. If, instead, absolute coastal sea levels or offshore sea-level differences are used to specify the along-shelf geostrophic current, the forecasting skill is 0.75. A characteristic El Niño/Southern Oscillation (ENSO) response is detected for time periods up to 25 years in monthly sea-level both at Townsville and at western Pacific island sea-level stations. This spatially coherent response varies in intensity and phase within the Coral Sea. Sea-level differences show a pattern which characterizes known features of the large-scale circulation of the Coral Sea. These very low frequency sea-level variations in the Coral Sea must be taken into account to obtain accurate predictions of along-shelf geostrophic current variations on seasonal and inter-annual time scales. Regression analysis and a diagnostic river plume model show that the influence of the major rivers can produce sea-level changes due to buoyancy of order 5 cm. The corresponding errors in geostrophic velocities estimated using pressure-adjusted Townsville sea-level data alone are of order 5 cm s−1 rms. 相似文献
17.
Impact of Sea-Level Rise on Sea Water Intrusion in Coastal Aquifers 总被引：17，自引：0，他引：17
Despite its purported importance, previous studies of the influence of sea-level rise on coastal aquifers have focused on specific sites, and a generalized systematic analysis of the general case of the sea water intrusion response to sea-level rise has not been reported. In this study, a simple conceptual framework is used to provide a first-order assessment of sea water intrusion changes in coastal unconfined aquifers in response to sea-level rise. Two conceptual models are tested: (1) flux-controlled systems, in which ground water discharge to the sea is persistent despite changes in sea level, and (2) head-controlled systems, whereby ground water abstractions or surface features maintain the head condition in the aquifer despite sea-level changes. The conceptualization assumes steady-state conditions, a sharp interface sea water-fresh water transition zone, homogeneous and isotropic aquifer properties, and constant recharge. In the case of constant flux conditions, the upper limit for sea water intrusion due to sea-level rise (up to 1.5 m is tested) is no greater than 50 m for typical values of recharge, hydraulic conductivity, and aquifer depth. This is in striking contrast to the constant head cases, in which the magnitude of salt water toe migration is on the order of hundreds of meters to several kilometers for the same sea-level rise. This study has highlighted the importance of inland boundary conditions on the sea-level rise impact. It identifies combinations of hydrogeologic parameters that control whether large or small salt water toe migration will occur for any given change in a hydrogeologic variable. 相似文献
18.
O. V. Pilipenko Z. V. Sharonova V. M. Trubikhin N. Abrahamsen 《Izvestiya Physics of the Solid Earth》2009,45(6):508-519
Paleomagnetic investigations of marine and subaqueous deposits in the 12-meter marine terrace of a section of the Karadzha Range (Azerbaijan) are performed. These deposits correspond to OI stage 3 and encompass the time interval ～45–20 ka. Four anomalous deviations of the magnetization from the dipole field at the sampling site are recorded in the upper and lower transgressive members of deposits. Investigations of the influence of the anisotropy of the magnetic susceptibility (AMS) on directions of the natural remanent magnetization (NRM) showed that only three of the four identified intervals can actually reflect geomagnetic field changes. The fourth interval of the anomalous NRM behavior is recorded in samples demonstrating the presence of the identified AMS direction pointing to a possible deformation of layers, which could turn the NRM vector toward the direction of the acting factor. Based on the age of the terrace under investigation, three other anomalous horizons could correspond to heavily reduced records of the Mono and Lashamp excursions of the geomagnetic field. 相似文献
19.
在较大地震的孕育过程中, 随着弹性应变能的不断积累, 孕震区有可能从原来的无序状态转变为一种在时间、 空间上的有序状态, 与之相联系的各种信息量的有序程度都有可能增加。 本文引入信息熵来描述前兆观测资料的空间扫描特征: 结果表明: 在4次福建地区中等地震前半个月至2个月, 在未来震中附近围成异常区域, 但异常表现各不相同, 异常区和异常量的大小与震级无明显关系, 震后异常区域均消失; 在4次地震中, 有1次地震发生在信息熵空间扫描围出的异常区内, 另外3次地震虽然不发生在异常区域内, 但震中都处于异常区域边缘, 最大距离不超过50 km以内, 这为判定震中位置提供了一定的依据。 相似文献
