Relocation of shallow earthquakes in southern Alaska using Joint Hypocenter Determination method     

Natalia A. Ratchkovsky  Jose Pujol  Niren N. Biswas 《Journal of Seismology》1998,2(1):87-102

A subset of 2660 shallow earthquakes (0–50 km) that occurred from 1988 to 1996 in south central Alaska between 155°W and 145°W and 59°N and 63°N was relocated using the joint hypocenter determination (JHD) method. Both P- and S-wave observations recorded by the regional seismic network were used. Events were relocated in twenty different groups based on their geographic location and depth using two velocity models. As a result of the relocation, the majority of the hypocenters shifted downward, while the epicenter locations did not change significantly. The distribution of the shallow subduction zone earthquakes indicates the existence of two seismically independent blocks, with one block occupying the northeastern part and the other occupying the central and western parts of the study area. The boundary between the blocks is marked by a 15 to 20 km wide seismicity gap to the southeast of 149.5°W and 62°N. The analysis of the fault plane solutions for shallow subduction zone earthquakes shows that an overwhelming majority of the solutions represent normal, oblique-normal or strike-slip faulting with predominant WNW-ESE orientation of T-axes. This indicates a down-dip extensional regime for the subducting slab at shallow depths. Very few earthquakes yielded fault plane solutions consistent with thrusting on a contact zone between the overriding and subducting plates. This result may be an indication that currently either the strain energy is not released at the contact zone or it is associated with aseismic motion.  相似文献   

Magnetic polarity zonation within the El Teniente copper–molybdenum porphyry deposit, central Chile     

Natalia Astudillo  Pierrick Roperch  Brian Townley  Cesar Arriagada  Annick Chauvin 《Mineralium Deposita》2010,45(1):23-41

El Teniente porphyry copper deposit, the world’s greatest intrusion-related Cu–Mo ore body, is hosted within basaltic–andesitic volcanic and gabbroic rocks (mafic complex). This ore body is strongly affected by multiple events of alteration/mineralization with pervasive potassic and chloritic alteration and coetaneous with associated copper mineralization. We present paleomagnetic results obtained from oriented samples at four locations within the mine and from two drill cores, 200 and 400 m long, respectively. Samples are representative of all the main hydrothermally altered rock units, with emphasis on the mafic host rock and dacitic (Teniente dacite porphyry) and dioritic porphyry intrusions. Magnetic experiments [hysteresis loop, isothermal remanent magnetization (IRM), k–T curves, thermal, and alternating field demagnetization] show the presence of prevailing magnetite. Microscope and SEM observations show two families of magnetite, (a) large multidomain magnetite grains, associated with biotite and chlorite of various different hydrothermal alteration events, and (b) abundant small to medium grain-size magnetite (<10 μm) contained within plagioclase, either related to an early Na–Ca–Fe alteration or included within plagioclase during magmatic crystal growth. While the Teniente dacite porphyry and the quartz diorite–tonalite have low magnetic susceptibility (<0.0005 SI) and low natural remanent magnetization (NRM, 10⁻⁴–10⁻³ Am⁻¹), the mineralized mafic host rocks have usually high susceptibility (>0.01 and up to 0.2 SI) with NRM in the range 0.1–2 Am⁻¹. Most mafic complex rock samples have univectorial magnetizations during alternating field or thermal demagnetization. Within the mine, the magnetic polarity is spatially distributed. In the northern part of the deposit, the Teniente dacite porphyry, the associated hydrothermal breccias, and the hosting mafic complex record a reverse polarity magnetization, also observed in the El Teniente sub-6 mine sector immediately to the east and southeast. In the eastern part of the deposit, a normal polarity is observed for samples of the mafic complex from the two long drill cores. There is no evidence for superimposed magnetizations of opposite polarities in samples of the mafic complex. Anhysteretic remanent magnetization (ARM) in a DC field of 40 μT and NRM have similar magnitude and comparable behavior upon alternating field demagnetization. The well-defined strong remanent magnetizations associated with high unblocking temperatures (>500°C) indicate an acquisition of remanent magnetization during mineralization by circulating high temperature fluids related with ore deposition. Paleomagnetic results and the recorded polarity zonation suggest multiple mineralization events occurred at El Teniente, each one with its own evolution stages, superimposed within the district. These results indicate that a simplified broad four-stage model for El Teniente, as presented and overly employed by many authors, divided in (1) late magmatic, (2) main hydrothermal, (3) late hydrothermal, and (4) posthumous stage, does not recognize various short-lived single mineralization events, some superimposed and some distinctly separated in time and space. There is no paleomagnetic evidence for post-mineralization deformation  相似文献   

A new key pole for the East European Craton at 1452 Ma: Palaeomagnetic and geochronological constraints from mafic rocks in the Lake Ladoga region (Russian Karelia)     

Natalia V. Lubnina  Satu Mertanen  Ulf Söderlund  Svetlana Bogdanova  Tatiana I. Vasilieva  Dmitry Frank-Kamenetsky 《Precambrian Research》2010

Palaeomagnetic and geochronological studies on mafic rocks in the Lake Ladoga region in South Russian Karelia provide a new, reliably dated Mesoproterozoic key paleopole for the East European Craton (Baltica). U–Pb dating on baddeleyite gives a crystallisation age of 1452 ± 12 Ma for one of the studied dolerite dykes. A mean palaeomagnetic pole for the Mesoproterozoic dolerite dykes, Valaam sill and Salmi basalts yields a paleopole at 15.2°N, 177.1°E, A₉₅ = 5.5°. Positive baked contact test for the dolerite dykes and positive reversal test for the Salmi basalts and for the dykes confirm the primary nature of the magnetisation. Comparison of this Baltica palaeopole with coeval paleomagnetic data for Laurentia and Siberia provides a revised palaeoposition of these cratons. The results verify that the East European Craton, Laurentia and Siberia were part of the supercontinent Columbia from the Late Palaeoproterozoic to the Middle Neoproterozoic.  相似文献   

Shaking table tests of a resilient bridge system with precast reinforced concrete columns equipped with springs     

Natalia Reggiani Manzo  Michalis F. Vassiliou  Harris Mouzakis  Efstratios Badogiannis 《地震工程与结构动力学》2022,51(1):213-239

This paper presents the shake table test results of a novel system for the design of precast reinforced concrete bridges. The specimen comprises a slab and four precast columns. The connections are dry and the columns are connected to the slab by an ungrouted tendon. One of the tendon ends is anchored above the slab, in series with a stack of washer springs, while the other end is anchored at the bottom of the column. The addition of such a flexible restraining system increases the stability of the system, while keeping it relatively flexible allowing it to experience negative post-uplift stiffness. It is a form of seismic isolation. Anchoring the tendon within the column, caps the design moment of the foundation, and reduces its size. One hundred and eighty-one shake table tests were performed. The first 180 caused negligible damage to the specimen, mainly abrasion at the perimeter of the column top ends. Hence, the system proved resilient. The 181^st excitation caused collapse, because the tendons unexpectedly failed at a load less than 50% of their capacity (provided by the manufacturer), due to the failure of their end socket. This highlights the importance of properly designing the tendons. The tests were used to statistically validate a rigid body model. The model performed reasonably well never underestimating the median displacement response of the center of mass of the slab by more than 30%. However, the model cannot predict the torsion rotation of the slab that was observed in the tests and is due to imperfections.  相似文献   

Melt Pockets in Garnet Megacrysts from Cenozoic Alkali Basalts of the Shavaryn Tsaram Vicinity, Mongolia     

Anna ASEEVA  Oleg AVCHENKO  Alexander KARABTSOV  Alexander CHASHCHIN  Sergey VYSOTSKIY  Victoria YAKOVENKO  Natalia ZARUBINA  Natalia KHARITONOVA 《《地质学报》英文版》2022,96(1):111-122

Garnet megacryst with a multiphase inclusion from intraplate alkali basalts of the Shavaryn Tsaram(Tariat,Mongolia)was the object of the study.This unusual aggregate consists of porous glass,Ti-rich biotite,orthopyroxene,spinel,clinopyroxene,olivine,and ilmenite.Win TWQ 2.32 thermodynamic simulation of this system revealed a few intervals of equilibrium.Pressure and temperature adjustment reflected in the paragenetic minerals of the melt pocket.The capture of already crystallised garnet megacryst was at P=0.8-1 GPa and T=1120-1160℃.Mineral crystallisation inside the melt pocket,accompanied by external inputs,occurred at P=0.75-0.95 GPa;T=790-1120℃.Symplectite assemblage formed in the garnet megacryst due to decomposition at(P=0.55-0.7 GPa;T=850-930℃).The study of the oxygen isotope content in primary garnet and biotite of the melt pocket showed that the δ¹⁸O_VSMOW values are the same and correspond to that of typical mantle xenoliths.However,the chemical and microcomponent composition of the melt pocket minerals reveals a material that differs from basalts and peridotites.Thus,it has been revealed that the multiphase inclusion in the garnet megacryst formed not only on account of the garnet’s substance,but also due to the entrapped material of the Earth’s interior.  相似文献   

Magnetic properties of the LL5 ordinary chondrite Chelyabinsk (fall of February 15, 2013)     

Natalia S. Bezaeva  Dmitry D. Badyukov  Mikhail A. Nazarov  Pierre Rochette  Joshua M. Feinberg  Gennadiy P. Markov  Daniel Borschneck  François Demory  Jérôme Gattacceca  Sergey E. Borisovskiy  Anna Ya Skripnik 《Meteoritics & planetary science》2014,49(6):958-977

Here we characterize the magnetic properties of the Chelyabinsk chondrite (LL5, S4, W0) and constrain the composition, concentration, grain size distribution, and mineral fabric of the meteorite's magnetic mineral assemblage. Data were collected from 10 to 1073 K and include measurements of low‐field magnetic susceptibility (χ₀), the anisotropy of χ₀, hysteresis loops, first‐order reversal curves, Mössbauer spectroscopy, and X‐ray microtomography. The REM and REM′ paleointensity protocols suggest that the only magnetizations recorded by the chondrite are components of the Earth's magnetic field acquired during entry into our planet's atmosphere. The Chelyabinsk chondrite consists of light and dark lithologies. Fragments of the light lithology show logχ₀ = 4.57 ± 0.09 (s.d.) (n = 135), while the dark lithology shows 4.65 ± 0.09 (n = 39) (where χ₀ is in 10^?9 m³ kg^?1). Thus, Chelyabinsk is three times more magnetic than the average LL5 fall, but is similar to a subgroup of metal‐rich LL5 chondrites (Paragould, Aldsworth, Bawku, Richmond) and L/LL5 chondrites (Glanerbrug, Knyahinya). The meteorite's room‐temperature magnetization is dominated by multidomain FeNi alloys taenite and kamacite (no tetrataenite is present). However, below approximately 75 K remanence is dominated by chromite. The metal contents of the light and dark lithologies are 3.7 and 4.1 wt%, respectively, and are based on values of saturation magnetization.  相似文献   

On the Sudden Depression of Radio Emission From Plasma Above a Fast-Moving Sunspot     

Natalia G. Peterova  Alexander A. Soloviev  G. Csepura 《Solar physics》2001,201(1):137-152

We present a very rare case of unexpected depression of radio emission above a sunspot using solar observations from RATAN-600. The sunspot had a very high proper motion on the solar surface. The depression lasted for 5 days without significant changes in area or magnitude of magnetic field of the associated sunspot. The observations show that the depression cannot be explained by the absorption of the emission during its propagation through the overlying magnetosphere of the AR or through the cold and opaque matter of a prominence. The theoretical interpretation of the phenomenon is based on the hypothesis that the motion of the sunspot on the photosphere leads to the significant expanding of the magnetic loop originated at this sunspot. The extension of the twisted magnetic rope results in the loss of equilibrium of the system: the closed magnetic structure (the twisted magnetic loop) seems destined to transform into an open one. The only mechanism of plasma heating which would be `switched off' in such a non-equilibrium configuration is that based on the quasi-static topological relaxation of a force-free magnetic field towards a configuration of minimum energy. Relaxation of magnetic fields does not occur in a non-equilibrium state. As a consequence, the energy release in the twisted magnetic rope and the temperature of the plasma of the local radio source have to fall down abruptly. Thus, the discussed phenomenon argues in favor of the relaxation model of plasma heating.  相似文献   

Foraminiferal responses to polluted sediments in the Montevideo coastal zone, Uruguay     

Burone L  Venturini N  Sprechmann P  Valente P  Muniz P 《Marine pollution bulletin》2006,52(1):61-73

A study of foraminiferal assemblages was carried out in 24 sediment samples collected from the Montevideo coastal zone (south-eastern coastal region of South America) to assess the response of the benthic foraminifera to the polluted sediments. The area is affected by different pollutants such as sewage, hydrocarbons and heavy metals derived from different sources. Biological data were analyzed with multivariate techniques of cluster analysis and a principal component analysis (PCA) was performed for abiotic factors. The results allowed the recognition of different species assemblages corresponding to different sub-environments, which reflected the prevalent ecological conditions. The Montevideo Bay, particularly, its inner part showed an extremely poor foraminiferal fauna-including a totally azoic station-and high percentages of abnormal tests, when compared with the adjacent Punta Carretas and Punta Yeguas zones. Mean faunal density showed a strong relationship with organic matter, oxygen and heavy metal concentrations, as well as redox potential and pH values of each sub-environment. Although the adjacent zones presented a moderate pollution degree, it was noticed that a positive effect on the foraminiferal density specially on Ammonia tepida, caused by the sewage pipe located in Punta Carretas, a pure organic contamination. Differences among foraminiferal assemblages seemed to be related to the combined action of the several kinds of pollutants and the natural abiotic variables, like the rapid salinity changes that occurred in this area.  相似文献   

Fractionation analysis of transport engine-generated soot particles with respect to hygroscopicity     

Elena D. Kireeva  Olga B. Popovicheva  Natalia M. Persiantseva  Mikhail A. Timofeyev  Natalia K. Shonija 《Journal of Atmospheric Chemistry》2009,64(2-3):129-147

Combustion-derived particles emitted by various transport engines are analyzed with respect to their morphology and composition. Soot particles collected behind an aircraft gas turbine engine combustor, in the diesel engine exhaust pipe, and at the end of ship pipe demonstrate heterogeneous morphological structures and different chemical identities. Individual particle analysis allows the characterization of emitted soot particles into three fractions, namely C-O, C-O-S, and Fe-C-O, with the dominant presence of chain soot agglomerates, irregular internally mixed soot, and particles of distinct morphology, respectively. The influence of oxygen and sulfur concentrations on the ability of soot to uptake water is proposed as a method for categorizing transport engine-generated particles. Categories of hydrophobic and hydrophilic particles within non-hygroscopic soots can be defined based on the amount of water uptake relative to several reference laboratory-made soots comparable to transport engine emissions. This method of characterizing hydrophobic/hydrophilic and hygroscopic soots in combustion emissions will help to determine the potential impacts of the combustion emissions on CCN/IN formation in the atmosphere.  相似文献   

Photometric function variations observed on the near side of the Moon: Mapping     

V. G. Kaidash  S. Yu. Gerasimenko  Yu. G. Shkuratov  N. V. Opanasenko  Yu. I. Velikodskii  V. V. Korokhin 《Solar System Research》2009,43(2):89-99

During two lunations, telescopic imaging of the near side of the Moon was performed at the Maidanak mountain observatory (Uzbekistan) with the use of digital cameras based on CMOS detectors. In different ranges of phase angles, the slope of the phase function of the lunar surface was mapped at a wavelength of 0.52 μm with the method of phase ratios. It has been shown that when the phase angle is gradually decreasing, the correlation between the phase-function slope and the albedo first disappears, and then even changes its sign at small phase angles.  相似文献