Electric currents along earthquake faults and the magnetization of pseudotachylite veins   总被引：2，自引：1，他引：2  

Friedemann Freund  Manuel A. Salgueiro da Silva  Bobby W.S. Lau  Akihiro Takeuchi  Hollis H. Jones 《Tectonophysics》2007,431(1-4):131

Pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes. They contain finely grained magnetite and often exhibit a high natural remanent magnetization (NRM). High NRM values imply strong local electric currents. These currents must persist for some time, while the pseudotachylite veins cool through the Curie temperature of magnetite around 580 °C. There is no generally accepted theory explaining how such powerful, persistent currents may be generated along the fault plane. Data presented here suggest the activation of electronic charge carriers, which are present in igneous rocks in a dormant, inactive form. These charge carriers can be “awakened” by the application of stress. They are electrons and defect electrons, also known as positive holes or p-holes for short. While p-holes are capable of spreading out of the stressed rock volume into adjacent p-type conductive unstressed rocks, electrons require a connection to the hot, n-type conductive lower crust. However, as long as the (downward) electron flow is not connected, the circuit is not closed. Hence, with the outflow of p-holes impeded, no current can be sustained. This situation is comparable to that of a charged battery where one pole remains unconnected. The friction melt that forms coseismically during rupture, provides a conductive path downward, which closes the circuit. This allows a current to flow along the fault plane. Extrapolating from laboratory data, every km³ of stressed igneous rocks adjacent to the fault plane can deliver 10³–10⁵ A. Hence, the current along the fault plane will not be limited by the number of charge carriers but more likely by the (electronic) conductivity of the cooling pseudotachylite vein. The sheet current will produce a magnetic field, whose vectors will lie in the fault plane and perpendicular to the flow direction.  相似文献   

Electrical Impedance Spectroscopy Used as a Tool for the Detection of Fractures in Rock Samples Exposed to either Hydrostatic or Triaxial Pressure Conditions   总被引：2，自引：0，他引：2  

Nover  G.  Heikamp  S.  Freund  D. 《Natural Hazards》2000,21(2-3):317-330

Pressure induced variations of the pore geometry werestudied by means of complex electrical dispersionmeasurements on natural marble (97% calcite, 3%quartz) and synthetic calcite samples (95% calcite,5% quartz; Siddiqi et al., 1997). Hydrostatic (up to 160 MPa) pressures were used toexamine the closing of fractures, whereas, triaxial pressures (P_c = 3 MPa; P_u = 1 to100 MPa) revealed information on forming and growth ofcracks. Porosity data ranged from 1 to 4 vol%.Permeabilities of the synthetic samples covered therange from 0.02 to 4 D, whereas the naturalmarble exhibited a permeability of less than 5 nD. BETinner surface areas ranged from 0.29 to 0.7m²/g. The frequency dispersion was measured inthe frequency range 1 kHz to 1 MHz. This frequencyrange is extensive enough to fit model data to themeasured data. The interpretation of the model datarevealed information on bulk conduction processes andinterfacial phenomena as well. The latter one isdirectly related to variations in the pore geometryand resulted in a correlation between the BET surfaceand the model parameter sensitive to the closing,opening, forming and growth of fractures. Asignificant `precursor' signal before failure wasfound in the triaxial experiments.  相似文献   

Fluctuations of electrical conductivity as a natural tracer for bank filtration in a losing stream     

Tobias Vogt  Eduard Hoehn  Philipp Schneider  Anja Freund  Mario Schirmer  Olaf A. Cirpka 《Advances in water resources》2010

A key parameter used in the assessment of bank filtration is the travel time of the infiltrated river water during the passage through groundwater. We analyze time series of electrical conductivity (EC) in the river and adjacent groundwater observation wells to investigate travel times of young hyporheic groundwater in adjoining channelized and restored sections of River Thur in North-East Switzerland. To quantify mixing ratios and mean residence times we perform cross-correlation analysis and non-parametric deconvolution of the EC time series. Measurements of radon-222 in the groundwater samples validate the calculated residence times. A simple relationship between travel time and distance to the river has not been observed. Therefore, we speculate that the lateral position and depth of the thalweg as well as the type of bank stabilization might control the infiltration processes in losing rivers. Diurnal oscillations of EC observed in the river and in nearby observation wells facilitate analyzing the temporal variation of infiltration. The diurnal oscillations are particularly pronounced in low flow situations, while the overall EC signal is dominated by individual high-flow events. Differences in travel times derived from diurnal and overall EC signals thus reflect different infiltration regimes.  相似文献   

Occurrence of copepod carcasses in the lower Chesapeake Bay and their decomposition by ambient microbes     

Kam W. Tang  Curtis S. Freund  Christopher L. Schweitzer 《Estuarine, Coastal and Shelf Science》2006,68(3-4):499

We tested and refined the Neutral Red staining method for separating live and dead copepods in natural samples. Live copepods were stained red whereas dead copepods remained unstained. The staining results were not affected by method of killing, time of death or staining time. Tow duration had no significant effect on the percent dead copepods collected. The Neutral Red staining method was applied to study the occurrence of dead copepods along the York River and the Hampton River in the lower Chesapeake Bay during June–July, 2005. The zooplankton community was dominated by copepods; on average 29% of the copepod population appeared dead. Recovery of percent dead copepods did not differ between horizontal tows and vertical tows, suggesting that dead copepods were homogenously distributed in the water column. No significant relationship was found between the percent dead copepods and surface water temperature, salinity, Secchi depth or chlorophyll concentration. In laboratory experiments, dead copepods were decomposed by ambient bacteria and the rate of decomposition was temperature-dependent. Combining field and laboratory results we estimated that the non-consumptive mortality (mortality not due to predation) of copepods in the lower Chesapeake Bay was 0.12 d⁻¹ under steady-state condition, which is within the global average of copepod mortality rate.  相似文献   

Electro-magnetic earthquake bursts and critical rupture of peroxy bond networks in rocks   总被引：2，自引：0，他引：2  

F. Freund  D. Sornette   《Tectonophysics》2007,431(1-4):33

We propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic and electric phenomena which have been associated with earthquakes. The mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress. The electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice, called peroxy bonds or positive hole pairs (PHP), where a PHP represents an O₃X/^OO YO₃ with X,Y = Si⁴⁺,Al³⁺,…, i.e. O⁻ in a matrix of O²⁻ of silicates. We propose that PHP are activated by plastic deformations during the slow cooperative build-up of stress and the increasingly correlated damage culminating in a large “critical” earthquake. Recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit. We conjecture that the intermittent and erratic occurrences of EM signals are a consequence of the progressive build-up of the battery charges in the Earth crust and of their release when crack networks percolate through the stressed rock volumes, providing a conductive pathway for the battery currents to discharge. EM signals are thus expected close to the rupture, either slightly before or after, that is, when percolation is most favored. The proposed mechanism should be relevant for the broader understanding of fractoemissions.  相似文献   

Preliminary mesozoic palaeomagnetic results from Israel and inferences for a microplate structure in the Lebanon     

R. Freund  D.H. Tarling   《Tectonophysics》1979,60(3-4):189-205

Preliminary results from a few Triassic, Jurassic and Cretaceous rocks indicate that Israel has behaved as part of the African plate during this period. Earlier palaeomagnetic results from the Lebanon, previously explained in terms of a separate Levantine plate, can be better explained in terms of differential motion between fault blocks in response to motions along the Dead Sea Fault. The available evidence allows determination of the net motions of specific fault blocks and is consistent with independent palaeogeographic indicators of the pretectonic relationship between these blocks.  相似文献   

Discussion of "A Comparison of Ground Water Monitoring Data from CERCLA and RCRA Sites," by Russell H. Plumb, Ground Water Monitoring Review, pg. 94, Fall 1987.     

Jerry R. Garman  Vernon B. Myers  chief  Thomas Freund  chemist 《Ground Water Monitoring & Remediation》1988,8(3):166-167

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Geochemistry of salt marsh sediments deposited during simulated sea-level rise and consequences for recent and Holocene coastal development of NW Germany   总被引：2，自引：2，他引：0  

Kerstin Kolditz  Olaf Dellwig  Jan Barkowski  Thomas H. Badewien  Holger Freund  Hans-Jürgen Brumsack 《Geo-Marine Letters》2012,32(1):49-60

De-embankment in the salt marshes of the island of Langeoog was carried out in 2004, thereby inducing an artificial transgression within an area of 2.2 km². Material from three suspended matter traps (SMTs) located along a N–S transect was collected monthly between January 2006 and February 2007. Besides geochemical (major and trace elements) and grain-size analyses, the duration and height of water cover were continuously measured by pressure gauges during the sampling period at two sites, thus revealing inundation frequency (max. 280 year⁻¹) and level (max. 2.4 m). Generally, the silt-dominated SMT material exhibits a geochemical composition similar to that of suspended particulate matter from the adjacent Wadden Sea. However, distinctly increasing enrichments of TOC, P, Mn and Mo from the shoreline towards the higher salt marsh clearly indicate fractionation processes during material transport. Geochemical comparison with older Holocene coastal deposits reveals a mixture of brackish and tidal flat sediments, thus reflecting an early stage of sea-level rise and the development from a terrestrial towards a marine-dominated system. Sedimentation rates are higher than the local sea-level rise, as revealed by vertical salt marsh growth. Storm surges deliver the highest amounts of sediment and play an important role in salt marsh accumulation within the study area. Average accumulation rates of TOC (780 t year⁻¹), P (54 t year⁻¹) and Mn (5.2 t year⁻¹) in the de-embanked area suggest that the former sand-dominated sediments currently receive significant amounts of reactive organic-rich material, thus fostering biogeochemical cycling.  相似文献   

Transcurrent Faults, Beam Theory and the Marlborough Fault System, New Zealand     

A. M. Merzer  R. Freund 《Geophysical Journal International》1974,38(3):553-562

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Carbon in olivine single crystals analyzed by the ¹²C(d,p)¹³C method and by photoelectron spectroscopy     

Gert Oberheuser  Hendrik Kathrein  Guy Demortier  Horst Gonska  Friedemann Freund 《Geochimica et cosmochimica acta》1983,47(6):1117-1129

Carbon subsurface concentration profiles in olivine single crystals from San Carlos, Arizona, and the Sergebet Island. Red Sea, containing total carbon between 60–180 wt.-ppm, were analyzed by means of the ¹²C(d. p)¹³C nuclear reaction and by x-ray induced photoelectron spectroscopy (XPS) in combination with acid etching and with Ar⁺ ion sputtering respectively, between 200–930 K. The (d, p) analysis reveals equilibrium subsurface C profiles extending 1–2 μm or more into the bulk. Their steepness is a function of temperature. Typical mean C concentrations at 300 K in the resolvable layers, 0–0.6, 0.6–1.2, and 1.2–1.8 μm. are 1.8, and 0.6 wt.-%, corresponding to enrichment factors over the mean bulk C concentration of the order of 100, 40 and 30 respectively. In the topmost atomic layers analyzed by XPS the carbon is enriched by a factor of the order of 1000, decreasing with increasing temperature. The results suggest that the carbon is in a truly dissolved state and highly mobile, subject to a reversible subsurface segregation. Most probably local lattice strain associated with the solute C species provide the driving force for this diffusional process. The C diffusion coefficient was determined from the (d, p) data below 300 K: D= 10^?13 exp(?7.8/RT) [m²· sec^?1; KJ · mole^?1] and from XPS data between 450–925 K: D = 10^?14 exp(-6/RT) [m² · sec^?1; KJ · mole^?1] The estimated error of the preexponential factors is ± one order of magnitude, that of the activation energies ±3.5 and ±2 KJ mole^?1 respectively.  相似文献