Interrelation among several important links in seismic risk analysis     

黄玮琼  吴宣 《地震学报(英文版)》2006,19(3):284-291

Introduction In the probability analysis method of seismic risk considering time-space inhomogeneity of seismic activity and adopted commonly in China (State Seismological Bureau, 1996) (called in-homogeneous distribution model for short), the division of seismic statistical regions, delimitation of potential seismic sources and estimation of seismicity parameters are the main links that affect significantly the estimation of ground motion parameters of a site. HUANG and WU (2005) studied …  相似文献   

Fine upper crustal structure of Jiashi strong earthquake swarm region in Xinjiang inferred from high resolution seismic refraction profile data     

徐朝繁张先康  段永红杨卓欣酆少英  胡修奇 《地震学报(英文版)》2006,19(1):62-71

Introduction Jiashi-Artux area in southwest Xinjiang is one of the most active earthquake provinces at pre-sent in Chinese mainland. In the last century, about 3/4 strong earthquakes in Chinese mainland hit this area, and especially from January 21 to April 16 in 1997, 7 earthquakes with the magnituderanging from 6.0 to 6.9 occurred in a very small area of 9 km×18 km near Jiashi (ZHU et al, 1998). It has never taken place before in Chinese mainland that a series of strong earthquakes shoo…  相似文献   

Upper mantle convection beneath northwest China and its adjacent region driven by density anomaly     

许萍傅容珊  黄建平查显杰 戴志阳 《地震学报(英文版)》2006,19(5):552-562

Introduction The northwest of China includes Tarim, Junggar and Qaidam basins, and Kunlun, Tianshan, Altun and Qilian mountains, as well as the north part of the Tibetan Plateau. For a long time, the study of lithosphere structures and dynamics in this area has been a popular topic in geoscience, and has yielded many results. For example, TANG (1994) and LI et al (1998) suppose that the tectonic structure of Tarim Basin is various with geological periods, which changes many times betwee…  相似文献   

Inversion of near-field waveform data for earthquake source rupture process (Ⅱ): Inversion of Chi Chi earthquake source, 20 September, 1999, Taiwan     

《中国科学D辑(英文版)》2006,(3)

The Chi Chi earthquake (Mw7.6) occurred at 17:47 UTC on Sept. 20,1999 (01:47 September 21, 1999, local time) in central Taiwan. CWB located the epi- center at (120.82°E; 23.85°N) and the focal depth 8 km. Chi Chi earthquake is the best documented earth- quake ever recorded. The abundance and quality of its near-source observations present an unparalleled op- portunity for studying the rupture history from a close distance. More than 400 free field digital accelerome- ters with 3-compon…  相似文献   

Lithium isotope fractionation in the southern Cascadia subduction zone   总被引：2，自引：0，他引：2  

Tom&#x; Magna  Uwe Wiechert  Timothy L. Grove  Alex N. Halliday 《Earth and Planetary Science Letters》2006,250(3-4):428-443

We present lithium (Li) abundances and isotope compositions for a suite of anhydrous olivine tholeiites (HAOTs) and hydrous basalt-andesitic (BA) lavas from the Mt. Shasta and Medicine Lake regions, California. The values of δ⁷Li vary from + 0.9‰ to + 6.4‰ and correlate inversely with distance from the trench. These data are consistent with continuous isotope fractionation of Li during dehydration of the subducted oceanic lithosphere, an interpretation corroborated by uniformly high pre-eruptive H₂O contents in basaltic andesites accompanied by high Li, Rb, Sr, Ba and Pb abundances. The subduction-derived component that was added to these hydrous magmas is shown to be very similar beneath both Mt. Shasta and Medicine Lake volcanoes despite characteristically distinct Li isotope compositions in the magmas themselves. More evolved andesites and dacites from Mt. Shasta have δ⁷Li from + 2.8 to + 6.9‰ which is identical with the range obtained for HAOTs and BA lavas from Mt. Shasta. Therefore, Li isotopes do not provide evidence for any other crustal component admixed to Mt. Shasta andesites or dacites during magmatic differentiation and magma mixing in the crust.  相似文献   

Characterization of volcanic thermal anomalies by means of sub-pixel temperature distribution analysis     

Valerio Lombardo  Maria Fabrizia Buongiorno  Stefania Amici 《Bulletin of Volcanology》2006,68(7-8):641-651

The simultaneous solution of the Planck equation (involving the widely used “dual-band” technique) using two shortwave infrared (SWIR) bands allows for an estimate of the fractional area of the hottest part of an active lava flow (f _h) and the background temperature of the cooler crust (T _c). The use of a high spectral and spatial resolution imaging spectrometer with a wide dynamic range of 15 bits (DAIS 7915) in the wavelength range from 0.501 to 12.67 μm resulted in the identification of crustal temperature and fractional areas for an intra-crater hot spot at Mount Etna, Italy. This study indicates the existence of a relationship between these T _c and f _h extracted from DAIS and Landsat TM data. When the dual band equation system is performed on a lava flow, a logarithmic distribution is obtained from a plot of the fractional area of the hottest temperature vs. the temperature of the cooler crust. An entirely different distribution is obtained over active degassing vents, where increases in T _c occur without any increase in f _h. This result indicates that we can use scatter plots of T _c vs. fh to discriminate between different types of volcanic activity, in this case between degassing vents and lava flows, using satellite thermal data.  相似文献   

Groundwater-level Changes Due to Pressure Gradient Induced by Nearby Earthquakes off Izu Peninsula, 1997     

Masao Ohno  Tsutomu Sato  Kenji Notsu  Hiroshi Wakita  Kunio Ozawa 《Pure and Applied Geophysics》2006,163(4):647-655

Anomalous water level changes were observed at two wells associated with seismic swarm activity off Izu Peninsula on March, 1997. These are coseismic water level drops followed by gradual postseismic water level rise at the time of large earthquakes during the swarm activity. The post-seismic water level rises, which can be fitted by an exponential function with a time constant of about six hours, are explained in terms of the horizontal pressure diffusion due to the pressure gradient in the aquifer induced by the coseismic static strain.  相似文献   

Carbon sources of fish in an Amazonian floodplain lake     

A. Cristina B. Oliveira  M. Gercilia M. Soares  L. Antonio. Martinelli  M. Zacarias. Moreira 《Aquatic Sciences - Research Across Boundaries》2006,68(2):229-238

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Seismicity before and after the two great Sumatra earthquakes of 2004 and 2005     

Sławomir Jerzy Gibowicz  Wojciech Dębski 《Acta Geophysica》2006,54(4):343-360

The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230 events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast. The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south.  相似文献   

Variations of near-surface atmospheric CO₂ and H₂O concentrations during summer on Muztagata     

Xu Baiqing  Yao Tandong  Lu Anxin  Guo Xuejun  Liu Xianqin  Li Zhen 《中国科学D辑(英文版)》2006,49(1):18-26

Expeditions during the summers of 2002 and 2003 implemented continuous monitoring of near-surface (2 m height) atmospheric CO₂ and H₂O concentrations at the 4500 m elevation on Muztagata. The resultant data sets reveal a slight decrease of CO₂ concentrations (of about 5 μmol·mol^-1) and changes in the diurnal variations from the end of June to the middle August. The daily maximum CO₂ concentrations occur between 02:30-05:30 AM (local time) and the minimum levels occur between 12:00-15:30 PM. The atmospheric CO₂ concentrations in the summer of 2002 were around 5 μmol·mol^-1 lower than those during the same period of 2003, whereas the diurnal amplitude was higher. In contrast, we found that the daily mean atmospheric H₂O content in 2003 was much lower than that in 2002 and there exists a striking negative correlation between CO₂ and H₂O concentrations. We therefore suggest that the near-surface atmospheric CO₂ concentration is affected not only by photosynthesis and respiration, but also by the air H₂O content in the glaciated region around Muztagata.  相似文献