首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 358 毫秒
1.
四川较场弧形构造与1933年叠溪地震发震构造的再讨论   总被引：5，自引：0，他引：5  
较场弧形构造是四川众多弧形构造带之一。本文对该弧形构造的特征及其西冀发育的松平沟断裂的新活动性作了进一步论证，确认松平沟断裂属全新世活动断裂。该弧形构造西翼弧顶部位1933年曾发生过叠溪7．5级地城,丧人对该次地震的发震构造众说纷纭。作者通过近年来在现场的多次考察，并对该次地震的等烈度线形态，地表震害展布特征，建筑物沿松平沟断裂的左旋位错，震后持表发育的西北向地震地裂缝等现象的进一步研究认为，1933年叠溪7．5级地震的发展震构造仍为较场弧形构造西翼的松平沟断裂。  相似文献   

2.
The history of organization and performance of the largest international scientific projects—the first International Polar Year (1882–1883), the second International Polar Year (1932–1933), and the International Geophysical Year (1957–1958)—and the significance of these projects for the development of geophysical studies in our country are briefly considered.  相似文献   

3.
Paleomagnetic measurements have been made on a continuously sampled, 5-m section of a core from Clear Lake, California. The sediments studied span an 8000-year interval centered at 25,000 years B.P., the approximate date of the large-scale, counterclockwise loop of the magnetic vector recorded in sediments from Mono Lake, California. The data from Mono Lake have been interpreted as a geomagnetic excursion with a duration of 600–1000 years. Because Clear Lake is only 320 km from Mono Lake and since each sample from Clear Lake represents 26 years of sedimentation, the magnetic signature of the Mono Lake geomagnetic excursion should be recorded in detail in the Clear Lake samples. Aside from a generally uniform shallowing of inclinations due to compaction, the paleomagnetic record from Clear Lake contains no anomalous features which would correspond to the Mono Lake excursion. Thus it has yet to be shown that the Mono Lake excursion was recorded anywhere besides Mono Lake. Even if the existence of the excursion is ultimately confirmed, its usefulness as a magnetostratigraphic horizon is limited.  相似文献   

4.
Tonle Sap Lake (TSL) is one of the world's most productive lacustrine ecosystems, driven by the Mekong River's seasonal flood pulse. This flood pulse and its long-term dynamics under the Mekong River basin's (MRB) fast socio-economic development and climate change need to be identified and understood. However, existing studies fall short of sufficient time coverage or concentrate only on changes in water level (WL) that is only one of the critical flood pulse parameters influencing the flood pulse ecosystem productivity. Considering the rapidly changing hydroclimatic conditions in the Mekong basin, it is crucial to systematically analyse the changes in multiple key flood pulse parameters. Here, we aim to do that by using observed WL data for 1960–2019 accompanied with several parameters derived from a Digital Bathymetry Model. Results show significant declines of WL and inundation area from the late 1990s in the dry season and for the whole year, on top of increased subdecadal variability. Decreasing (increasing) probabilities of high (low) inundation area for 2000–2019 have been found, in comparison to the return period of inundation area for 1986–2000 (1960–1986). The mean seasonal cycle of daily WL in dry (wet) season for 2000–2019, compared to that for 1986–2000, has shifted by 10 (5) days. Significant correlations and coherence changes between the WL and large-scale circulations (i.e., El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Indian Ocean Dipole (IOD)), indicate that the atmospheric circulations could have influenced the flood pulse in different time scales. Also, the changes in discharge at the Mekong mainstream suggest that anthropogenic drivers may have impacted the high water levels in the lake. Overall, our results indicate a declining flood pulse since the late 1990s.  相似文献   

5.
The Jiaocbang arcuate structure is one of the numerous arcuate structural belts in Sichuan. The present paper gives a further argument about the characteristics of that arcuate structure and the new activity of the Songpinggou fault and affirms that the Songpinggou fault is an active fault in the Holocene epoch. The Diexi M7.5 earthquake took place in 1933 on the west wing of that arcuate structure, near the apex of the arc. Many authors have given quite different opinions about the genetic structure of that earthquake. The authors have made on-the-spot investigations time and again over recent years. Besides this, the authors have also further studied the shape of intensity contour lines, the distribution characteristics of ground surface seismic hazards, the left-lateral dislocation of buildings along the Songpinggou fault, the NWtrending ground fissures that developed on the ground surface after earthquake, and so on. On this basis, it is still considered that the seismogenic fault of the 1933 Diexi M7.5 earthquake was the Songpinggou fault on the west wing of the Jiaochang arcuate structure.  相似文献   

6.
The Jiaochang arcuate structure is one of the numerous arcuate structural belts in Sichuan. The present paper gives a further argument about the characteristics of that arcuate structure and the new activity of the Songpinggou fault and affirms that the Songpinggou fault is an active fault in the Holocene epoch. The Diexi M7.5 earthquake took place in 1933 on the west wing of that arcuate structure, near the apex of the arc. Many authors have given quite different opinions about the genetic structure of that earthquake. The authors have made on-the-spot investigations time and again over recent years. Besides this, the authors have also further studied the shape of intensity contour lines, the distribution characteristics of ground surface seismic hazards, the left-lateral dislocation of buildings along the Songpinggou fault, the NWtrending ground fissures that developed on the ground surface after earthquake, and so on. On this basis, it is still considered that the seismogenic fault of the 1933 Diexi M7.5 earthquake was the Songpinggou fault on the west wing of the Jiaochang arcuate structure.  相似文献   

7.
Long-time series of high-resolution temperature record from Chinese Loess Plateau is rare. An April-September mean temperature reconstruction (1826-2004) has been developed for the north-central Shaanxi Province, China, based on tree-ring width analysis. The reconstruction captures 39.3% (p<0.001) of the variance in the instrumental data over the calibration period from 1951 to 2002. The reconstruction shows a high temperature period of 1928-1933, which coincides with the timing of the extreme drought event in 1920s in the entire northern China. The two low temperature periods in reconstruction are 1883-1888 and 1938-1942. With the global warming, the April-September mean temperature in study area has also increased since the 1970s, but has not exceeded the temperature in 1928-1933. Besides the statistical analysis, the reconstruction is also verified by the local dryness/wetness index and other dendroclimatological results.  相似文献   

8.
叙述了翁文灏、谢家荣、王竹泉、李善帮等地震科学研究的开拓者对１９１３年云南峨山、１９１７年安徽霍山、１９２０年海原、１９３３年四川叠溪、１９３６年灵山、１９３７年山东菏泽等大地震进行的现场科学考察情况以及研究成果，指出这些成果和论著是中国近现代地震科学的奠基之作。认为，认真借鉴前人的研究成果，对地震科学的进步与发展，大有裨益。  相似文献   

9.
40Ar/39Ar age determinations have been carried out on eight samples of melt rocks and one of the maskelynite from Mistastin Lake impact crater, Labrador. The observed40Ar* evolution spectra of the impact melts fall into distinct groups which correlate with petrographic variations. The release patterns of six of the melt rock samples define an age plateau in the range 34–41 m.y.; the other two have complex spectra which indicate incomplete equilibration of inclusions. Four of the samples with well-defined plateaux exhibit a high-temperature sag in their40Ar/39Ar ratio similar to that observed in some lunar samples. Maskelynite gives a partially overprinted spectrum which rises monotonically to a final age near 700 m.y., approximately half the age of the country rocks. The data from the melt samples are interpreted as indicating an age of 38 ± 4 m.y. for the Mistastin Lake impact event. Previously, it had been considered that this crater was 202 ± 25 m.y. old.  相似文献   

10.
Summary Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Toolangi during two ten year periods (1924–1933 and 1949–1958) have been analysed to determine their solar and luni-solar diurnal components. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. It is shown that there are marked differences in the dependence ofS andL on the various parameters and a tentative explanation of this phenomenon is given.  相似文献   

11.
Mountain Lake is the only natural lake of significance in the unglaciated southern Appalachian Highlands. It is located near the summit of Salt Pond Mountain, Giles County Virginia, at an elevation of 1177 m. It is underlain by Ordovician and Silurian non‐calcareous shale and sandstone of the Martinsburg, Juniata and Clinch formations. Historical (250 years) and sediment (6000 years) records suggest that the size of the lake has varied periodically. In the 1930s lake origin was proposed as due to valley damming by a lateral landslide (Hutchinson and Pickford, 1932) or damming by scree (Sharp, 1933). A later theory modified the landslide hypothesis to the primarily vertical collapse of a canyon feature in the Clinch (Parker et al., 1975). Fracture trace analysis now reveals a regional lineation feature associated with the lake. This feature is present surficially both downgradient from the lake to the northwest, and upgradient to the southeast. Sonar bathymetry and diver reconnaissance show it expressed as a (relatively sediment‐free) narrow open crevice in the deepest (33 m) portion of the lake, probably a fault. Hydrologic observation and resistivity suggest preferential water movement along this fracture, as well as leakage directly from the lake. The present study suggests conduit erosion within this feature and periodic vertical downsettling of overlying Clinch material as the primary mechanism of lake origin and water‐level fluctuations through time. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

12.
Long-term dynamics of water level in Lake Nero (1930–2011) has been analyzed. Pronounced trends, determined by the climate and anthropogenic components have been identified. Up to the 1970s, at a drop in lake water level, the ecosystem still showed the main features of a shallow water body overgrown with macrophytes. Water level rise caused a more intense development of phytoplankton, an increase in biogenic element concentrations, a decrease in water transparency and the contribution of cyanobacteria of S1 codon; pondweed disappeared almost completely. Step-by-step regression analysis of phytoplankton development indices and hydrological characteristics showed that water transparency in Lake Nero depends by 80% directly on water exchange and inversely on the concentration of chlorophyll a in seston. The main hypothesis of the study was confirmed: the key trigger in phytoplankton–macrophytes competition is water level rise.  相似文献   

13.
The Northern Zhongtiaoshan Fault is a major deep fault at the southern margin of the Yuncheng Basin. There have been few studies on the fault, and the historical earthquakes are few and weak. However, the intensity of activity on the fault should never be underestimated. Through interpretations of aerial images, topography measurements and excavation of trenches, this paper studied the fault distribution, the surface deformation and the activity of the normal fault south of Salt Lake near the city of Yuncheng. By tracing faults in the three trenches, it was found that there had been at least three large paleoseismic events, at 1–3.5, 3.6–4.4 and 7.4–8.8 ka BP. Employing 14 C dating, we determined the same gravel layers in the uplifted side and downthrown side. Making differential Global Positioning System measurements of the vertical difference and topographic profile, we obtained the mean slip rate of the Northern Zhongtiaoshan Fault since 24.7 ka BP(0.75±0.05 mm/a). Using the results of relevant studies, we calculated the possible vertical fault displacement of one earthquake(2.35 m) and obtained the recurrence interval of characteristic earthquakes as 2940–3360 a after dividing the displacement by the mean slip rate.  相似文献   

14.
Field data, supported by 2814C dates, show that during the late Pleistocene Lake Bosumtwi suffered a major regression and probably remained low for some time, the exposed lacustrine sediments undergoing considerable pedogenesis. Just after 13,000 B.P. the lake was rising again, and thereafter the crater has generally been characterised by a lake significantly higher than it is at present. These periods of high water level, of 2000–2500 years duration, were interrupted by short, but intense regressions centred around 10,500, 8000, 4000–4500 and just after 1000 years B.P. During the highstands the local climate is likely to have been broadly similar to today; the nature of the climatic changes responsible for the regressions is not known with any certainty.  相似文献   

15.
The article presents the results of hydrochemical studies of two areas, open and closed, in the littoral zone of Lake Onega, carried out in 2013–2014. The results show that water of river and slope runoff, enriched with both biogenic elements and allochthonous organic matter, persist over a long time in spring in the littoral zone. In the summer, water chemistry at open shores is similar to that in lake pelagic zone, while the closed areas of littoral zone show the effect of biological processes. In the period of autumn homothermy, river and slope waters have no considerable effect on coastal water quality.  相似文献   

16.
本文记述了1933年叠溪地震后的调查、报道和研究,重点介绍了中国西部科学院的叠溪地震调查及其著述《四川叠溪地震调查记》。关于叠溪地震,这是第一次科学性的现场调查和第一篇学术报告,具有重要的学术参考价值。  相似文献   

17.
研究了 1900年以来台湾及东部海域强震 (M≥ 7)时空分布特征,收集和测定了 1933年以来强震震源机制解。 结果表明,台湾及东部海域存在 3个强震活动带及 4个活跃时段。 29个强震震源机制解较好地反映了 3个地震活动带的区域应力场特征和力源。 研究认为,台湾及东部海域自 1986年开始的第四活跃时段与大陆地区强震活动的第五活跃期有同期活动特点。 据推测,我国大陆和台湾的强震活动可能还要持续一段时间。  相似文献   

18.
Abstract

Hydrogeological investigations have been carried out in rural parts of Guntur district, Andhra Pradesh, India where agriculture is the main occupation. Granite gneisses associated with schists and charnockites are the main lithological formations, which are overlain by black cotton soils. Groundwaters are alkaline, very hard and mostly brackish. Possible sources of fluoride (F?) are weathering and leaching of F?-bearing minerals under the alkaline environment. A high rate of evapotranspiration, longer residence time of waters in the aquifer zone, intensive and longterm irrigation, and heavy use of fertilizers are the supplementary factors to further increase the F? content in the groundwaters. The investigated area has been classified into three types with reference to concentration of F- prescribed for drinking: low-F- (<0.60 mg l?1), moderate-F? (0.60–1.20 mg l?1) and high-F- (>1.20 mg l?1). Forty-five percent of the total groundwater samples belong to the high-F- category. Dental fluorosis is noticed in the region. A groundwater management programme is suggested.  相似文献   

19.
The hydrodynamic processes in the Lake of Lugano (Lago di Lugano) have been the object of three major measuring campaigns. The first during summer 1979 in the North Basin, the second in the autumn of 1984 in the South Basin and the last in 1989 again in the North Basin. It is expected that analysis of the collected data in conjunction with theoretical concepts will yield conclusive findings on the driving forces and hydrodynamics of the lake. Numerical models have been applied to the lake and the results have been compared to the measurements. Some models calculate the periods and distributions of amplitude, as well as surface velocities and internal seiches. Other models calculate wind-induced water circulation. Evidence is given to the peculiarities of the North Basin and the difficulties related with the depth-width ratio and with its deep chemical stratification.  相似文献   

20.
Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 106 m3 year?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号