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1.
Apoyeque volcano, located 9 km northwest of Managua city, erupted explosively at 12.4 ka. The Plinian eruption deposited a widespread pumice fall deposit known as the Upper Apoyeque Tephra (UAq). The UAq is massive, reversely graded, and consists of white juvenile pumice (~78 vol.%), a variety of cognate lithics and accidental altered lithics. The whole-rock pumice composition is rhyodacitic (SiO2?=?66.9–68.5 wt.%) with a mineral paragenesis of plagioclase, orthopyroxene, clinopyroxene, amphibole, titanomagnetite, and ilmenite in a rhyolitic glass groundmass (SiO2?=?74.4?±?0.6 wt.%). The deposit’s dispersal axis is to the south, with the deposit covering a minimum area of 877 km2 within the 50 cm isopach and has a total volume of 3 km3 (dense rock equivalent, 1.15 km3). The eruption column reached a maximum height of ca.28 km. The eruption ejected a total mass of 3?×?1012 kg at an average rate of 2?×?108 kg/s, and based on available models, we infer duration of almost 4 h. Petrographic and geochemical characteristics suggest that the eruption was triggered by magma mixing.  相似文献   

2.
Number 1Features,Impacts and Causes of the High Temperature and Large Precipitation Event in the Tibetan Plateau and Its Adjacent Area During 40———30kaBP··············-····-·-···-··-·SHI Ya.feng,JIA Yulian,YUGe,yANG Dayuan,FAN Yunqi,LJ Shijie,暇NG Yun乃j(11)Construction of Flood Control Engineering and Countermeasures for Flood Disaster Mitiga— tion in Taihu Basin………………………………………………………………LJN Zexin(18)Dynamic Water——Lev…  相似文献   

3.
On 22 January 2003, the M w?=?7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0?km in depth and 1.4?km in the north?Csouth and east?Cwest directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8?km in depth, 0.3?km in the east?Cwest direction, and 0.7?km in the north?Csouth direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3?months after the mainshock.  相似文献   

4.
 The 1982 eruption of El Chichón volcano ejected more than 1 km3 of anhydrite-bearing trachyandesite pyroclastic material to form a new 1-km-wide and 300-m-deep crater and uncovered the upper 500 m of an active volcano-hydrothermal system. Instead of the weak boiling-point temperature fumaroles of the former lava dome, a vigorously boiling crater spring now discharges  / 20 kg/s of Cl-rich (∼15 000 mg/kg) and sulphur-poor ( / 200 mg/kg of SO4), almost neutral (pH up to 6.7) water with an isotopic composition close to that of subduction-type magmatic water (δD=–15‰, δ18O=+6.5‰). This spring, as well as numerous Cl-free boiling springs discharging a mixture of meteoric water with fumarolic condensates, feed the crater lake, which, compared with values in 1983, is now much more diluted (∼3000 mg/kg of Cl vs 24 030 mg/kg), less acidic (pH=2.6 vs 0.56) and contains much lower amounts of S ( / 200 mg/kg of SO4, vs 3550 mg/kg) with δ34S=0.5–4.2‰ (+17‰ in 1983). Agua Caliente thermal waters, on the southeast slope of the volcano, have an outflow rate of approximately 100 kg/s of 71  °C Na–Ca–Cl water and are five times more concentrated than before the eruption (B. R. Molina, unpublished data). Relative N2, Ar and He gas concentrations suggest extensional tectonics for the El Chichón volcanic centre. The 3He/4He and 4He/20Ne ratios in gases from the crater fumaroles (7.3Ra, 2560) and Agua Caliente hot springs (5.3Ra, 44) indicate a strong magmatic contribution. However, relative concentrations of reactive species are typical of equilibrium in a two-phase boiling aquifer. Sulphur and C isotopic data indicate highly reducing conditions within the system, probably associated with the presence of buried vegetation resulting from the 1982 eruption. All Cl-rich waters at El Chichón have a common source. This water has the appearence of a "partially matured" magmatic fluid: condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in S due to anhydrite precipitation. Shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits (Red waters) are Ca–SO4–rich and have a negative oxygen isotopic shift, probably due to ongoing formation of clay at low temperatures. Received: 21 July 1997 / Accepted: 4 December 1997  相似文献   

5.
ＳｏｕｒｃｅｐａｒａｍｅｔｅｒｓｏｆｔｈｅＧｏｎｇｈｅ，ＱｉｎｇｈａｉＰｒｏｖｉｎｃｅ，Ｃｈｉｎａ，ｅａｒｔｈｑｕａｋｅｆｒｏｍｉｎｖｅｒｓｉｏｎｏｆｄｉｇｉｔａｌｂｒｏａｄｂａｎｄｗａｖｅｆｏｒｍｄａｔａＬＩ－ＳＨＥＮＧＸＵ（许立生）ａｎｄＹＵＮ...  相似文献   

6.
The Temté basement in North Cameroon is crosscut by dyke swarms with N 20°–40° trending,including dykes 15–30 m wide, up to 3 km-long. Representative rocks exhibit intersertal to sub-ophitic textures.Electron microprobe analyses identified diopside, augite,pargasite, biotite, Ti-magnetite, plagioclase, and sanidine.Whole-rock ICP-MS and ICP-AES chemical analyses showed compositions of basaltic andesite, basaltic trachyandesite and trachyandesite in composition. Igneous differentiation was likely governed by fractional crystallization associated with limited fluid metasomatism. Some lavas could have been moderately contaminated by crustal materials during feeding of local cracks through turbulent magma flows. Discrimination geochemical diagrams and immobile trace and REE element ratios show that the mantle source of Temté dolerites was a deep phlogopitebearing EMII mantle component and has undergone moderate to high partial melting rate. Correlations of fieldwork and analytical data with previous results evidence the Temté dolerite dyke swarms as fingerprints of crustal extension accompanying regional uplift in an active continental margin when early rifting led to the formation of the Poli marginal basin.  相似文献   

7.
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8.
Introduction The June 4, 2000 southern Sumatra, Indonesia, earthquake (16h28min26.2s UTC, 4.72, 102.09, 33 km, MS=8.0 [IRIS]) occurred under the Indian Ocean, near the Mentawai fault, along the well-known Sumatran subduction zone and the great Sumatran fault, all of which trend northwest-southeast. 1 800 houses were totally destroyed, 10 196 were heavily damaged, and 18 378 were slightly damaged by the earthquake. At least 97 people were killed, 1 900 were injured, and 122 000 were left…  相似文献   

9.
As is well known, researches on rupture process of earthquakes can not only deepen our understanding of earthquake occurrence, but also help to achieve earthquake prediction, which is one of the most difficult scientific problems in the world. Seismologists always pay great attention to it. Since the beginning of 1990s, they have aimed at the time-space variation of earthquake source rupture during the mainshock. In their works the digital data of seismic waves are inverted for the rupture pro…  相似文献   

10.
~~The role of aerial algae in the formation of the landscape of the Yunnan Stone Forest,Yunnan Province, China~~  相似文献   

11.
Analyses of rock-magnetic properties of Neogene sediments of the Taxihe section, northern Tianshan Mountains, show that the section can be classified into three categories including lacustrine facies, fluvial facies and alluvial facies, which correspond to the lower, middle and upper of the Taxihe section respectively. The magnetic minerals of the lacustrine facies may be affected by the process of weath- ering, lithogenesis and biolithogenesis besides the source of the sediments. The natural remanence intensities are between 10-3 A/m and 10-2 A/m. The minerals are dominated by magnetite and the high coercive magnetic mineral may be goethite. The magnetic grains are the mixture of PSD SD or SD SP. The natural remanence intensities of the strata of fluvial facies are between 10-2 A/m and 10-1 A/m, about ten times that of the lacustrine facies. The magnetic minerals are mainly magnetite and hematite, and the magnetic grains are mainly PSD. The characteristic remanence (ChRM) carriers are magnetites. In the alluvial facies, the natural remanence intensities are mostly less than 1×10-2 A/m. The magnetic minerals of the series are dominated by magnetite and hematite, almost the same as the fluvial facies. But the difference is that most of the stepwise demagnetization can reveal two components and the ChRM carriers are hematites. The magnetic grains are PSD in terms of the hysteresis parameters.  相似文献   

12.
Introduction An earthquake could be caused by the failure of focal material or fast slip on the pre-existed faults under the tectonic stress based on the understanding of the occurrence process of earth-quakes in which the stress change could play a key role. Therefore to examine the stress change is beneficial to understanding the physic process actually occurring in the source region deeply. The apparent stress is defined as the product of seismic efficiency and the average stress on the foc…  相似文献   

13.
ＲｕｐｔｕｒｅｐｒｏｃｅｓｏｆＮｏｖｅｍｂｅｒ６,１９８８,ＬａｎｃａｎｇＧｅｎｇｍａ,Ｙｕｎｎａｎ,Ｃｈｉｎａ,ｅａｒｔｈｑｕａｋｅｏｆＭｓ＝７．６ｕｓｉｎｇｅｍｐｉｒｉｃａｌＧｒｅｎ’ｓｆｕｎｃｔｉｏｎｄｅｃｏｎｖｏｌｕｔｉｏｎｍｅｔｈｏｄ...  相似文献   

14.
Ｃａｔａｌｏｇｕｅｏｆｅａｒｔｈｑｕａｋｅｓ（Ｄｅｃｅｍｂｅｒ，１９９３──Ｆｅｂｒｕａｒｙ，１９９４）Ｐｅｉ－ＳｈａｎＣＨＥＮ（陈培善）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，Ｂｅｉｊｉｎｇ１...  相似文献   

15.
Ｃａｔａｌｏｇｕｅｏｆｅａｒｔｈｑｕａｋｅｓ（Ｄｅｃｅｍｂｅｒ，１９９４－Ｆｅｂｒｕａｒｙ，１９９５）Ｐｅｉ－ＳｈａｎＣＨＥＮ（陈培善）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，Ｂｅｉｊｉｎｇ１０...  相似文献   

16.
The glacial records of the inner-core regions of the Laurentide Ice Sheet (LIS) document complex yet coherent patterns reflecting ice-sheet change (e.g. ice-divide migration), providing unique insights into past glacial conditions. This study develops a conceptual model of subglacial dynamics evolution within a major ice-dispersal centre of the LIS in northeastern Quebec, Canada using a GIS-based analysis of the surficial geologic record. Multiple proxies of subglacial conditions (subglacial streamlined landforms, lake density and lake area over thin drift/bedrock) were analysed through grid-overlay techniques and then classified based on different proxy variables ranging from highly mobile warm-based to immobile cold-based conditions. An additional proxy (till blanket) was used to identify areas of thick till deposition, but with few proxies (few lake or landform metrics). Based on local ice-flow reconstructions, the most ‘relict’ glacial terrain zone (GTZ1) has warm-based conditions over 66% of its area and is remarkably well preserved, suggesting laterally extensive warm-based conditions during the oldest identified ice-flow phase. This relict glacial terrain is partially overprinted by two subsequent ice-flow phases in spatially restricted zones in the northeast (73% warm-based), east-central (41% warm-based), and northwest (33% warm-based) of the study area. A zone of more sluggish conditions (only 3% warm-based) was identified in the highlands at the centre of the study area, characterized by thin till cover, few landforms, yet with large patches of relatively abundant small lakes, indicative of areal scouring. No clear evidence of sustained cold-based conditions (i.e. high chemical index of alteration values or high 10Be abundances) was found in the study area. These results suggest that warm-based conditions (active erosion and/or deposition) were uniformly widespread during the earliest ice-flow phase, later becoming more spatially restricted with broader sluggish ice conditions. These spatially restricted regions of warm-based subglacial regimes were likely controlled by surrounding and down-flow ice streaming. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

17.
An ASKANIA borehole tiltmeter which consists of a vertical pendulum with two degrees of freedom was installed in Xiangshan station,Beijing,in May 1989 in order to monitor the earthquake-reiated crustal deformations.The preliminary results indicate that the resolution of the instrument is better than 0.05 msec for tidal amplitudes.The daily total tidal amplitude is about 20 msec.The spectral analysis of the first four months data provides a signal-to-noise ratio of > 100 for the main semi-diurnal waves.The non-tidal tilts for one year data are dominated by a long term drift with the rate of 0.9 msec/day for X-component and 1.1 msec/day for Y-component.In addition,the tilt observations are affected by meteorological factors,especially by rainfall.The results of modelings of the fault-creep related tilts and responses of tilts to earthquakes suggest that the tilt measurements are very sensitive to the change in tectonic strain and stress fields near the site where the tiltmeter is installed.The fault-creep  相似文献   

18.
Introduction The unexpected December 26, 2004, off the west coast of northern Sumatra, Indonesia, MW=9.0 earthquake, which caused devastating tsunami around the Indian Ocean, reminds seis-mologists of the difficulty of earthquake forecast and/or prediction. For seismologists this earth-quake is almost completely unexpected, because there was neither forecasting (which means the estimation of the future earthquake rate as a function of location, time, and magnitude) nor predic-tion (forecasti…  相似文献   

19.
IntroductionSeismic wave is an important information source to analyze and study seismic source and internal structure of the earth. Studies of wave on different frequency ranges can provide many features of seismic source and internal structure of the earth. In recent years in quantitative study of seismic wave seismologists at home and abroad have developed a wide study field on the coda. Especially seismologists have done a lot of work in coda geneses, mechanism and its attenuation to explo…  相似文献   

20.
The first-order perturbation approximation is applied to calculate the rate coefficients of vibrational energy transfer in collisions involving vibrationally excited molecules in the absence of non-adiabatic transitions. The factors of molecular attraction, oscillator frequency change, anharmonicity, 3-dimensionality and quasiclassical motion have been taken into account in the approximation. The analytical expressions presented have been normalized on experimental data of VT-relaxation times in N2 and O2 to obtain the steric factors and the extent of repulsive exchange potentials in collisions N2–N2 and O2–O2. The approach was applied to calculate the rate coefficients of vibrational-vibrational energy transfer in the collisions N2–N2, O2–O2 and N2–O2. It is shown that there is good agreement between our calculations and experimental data for all cases of energy transfer considered.  相似文献   

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