Editorial. Geomorphological sociology     

Michael Church  Basil Gomez  Edward J. Hickin  Olav Slaymaker 《地球表面变化过程与地形》1985,10(6):539-540

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Continuation of the San Andreas fault system into the upper mantle: Evidence from spinel peridotite xenoliths in the Coyote Lake basalt, central California     

Sarah J. Titus  L. Gordon Medaris  Jr.  Herbert F. Wang  Basil Tikoff 《Tectonophysics》2007,429(1-2):1-20

The Coyote Lake basalt, located near the intersection of the Hayward and Calaveras faults in central California, contains spinel peridotite xenoliths from the mantle beneath the San Andreas fault system. Six upper mantle xenoliths were studied in detail by a combination of petrologic techniques. Temperature estimates, obtained from three two-pyroxene geothermometers and the Al-in-orthopyroxene geothermometer, indicate that the xenoliths equilibrated at 970–1100 °C. A thermal model was used to estimate the corresponding depth of equilibration for these xenoliths, resulting in depths between 38 and 43 km. The lattice preferred orientation of olivine measured in five of the xenolith samples show strong point distributions of olivine crystallographic axes suggesting that fabrics formed under high-temperature conditions. Calculated seismic anisotropy values indicate an average shear wave anisotropy of 6%, higher than the anisotropy calculated from xenoliths from other tectonic environments. Using this value, the anisotropic layer responsible for fault-parallel shear wave splitting in central California is less than 100 km thick. The strong fabric preserved in the xenoliths suggests that a mantle shear zone exists below the Calaveras fault to a depth of at least 40 km, and combining xenolith petrofabrics with shear wave splitting studies helps distinguish between different models for deformation at depth beneath the San Andrea fault system.  相似文献   

Latitudinal and solar-cycle dependence of the interplanetary magnetic field predominant polarity     

Xenophon Moussas  Basil Tritakis 《Solar physics》1982,75(1-2):361-375

A study of the predominant interplanetary magnetic field (IMF) polarity is made, for the time period 1957–1977. The examination of the mean positive and negative sector width for time periods (semesters) for which the Earth was in northern and southern heliolatitudes shows that the predominant polarity for every semester follows, up to a certain extent, the Rosenberg-Coleman effect. However, the statistical support is not satisfactory. The same conclusion was pointed out by a similar study of data grouped over various phases of the solar cycle.Additionally the relative frequency of positive (negative) IMF polarity days, appeared over a mean solar rotation, shows that the general pattern of the mean IMF has a tendency to reoccur in the homologous (corresponding) phases of different solar cycles.  相似文献   

A solar cycle variation of the interplanetary magnetic field configuration     

Basil P. Tritakis 《Solar physics》1979,63(1):207-215

The representation of the sector boundaries, published by Svalgaard (1974, 1975) in a superposed 27-days Bartels format showed that they have a significant preference to occur in certain days of the solar rotation. Further study of these data, as well as of the polarized days in the vicinity of them, pointed out that during the epoch of extrema of the 11-year cycle there is a well-established 2-sector structure, on the average. On the contrary, a mean 4-sector structure is more prominent during the intermediate years.  相似文献   

‘Thermohaline front’ off the east coast of India and its generating mechanism     

Hareesh Kumar  Panangattu Viswanathan  Mathew  Basil  Ramesh Kumar  Madathiparambil Ranganatha  Raghunadha Rao  Akula  Jagadeesh  Puvvala Surya Venkata  Radhakrishnan  Kalarickal Gopalan  Shyni  Thiyyadi Nandakumar 《Ocean Dynamics》2013,63(11):1175-1180

Physical oceanography measurements reveal a strong salinity (0.18 psu km⁻¹) and temperature (0.07 °C km⁻¹) front off the east coast of India in December 1997. T–S diagrams suggest lateral mixing between the fresh water at the coast and the ambient warmer, saltier water. This front seems to be the result of southward advection of fresh and cool water, formed in the northern Bay of Bengal during the monsoon, by the East Indian Coastal Current, as suggested by the large-scale salinity structure in the SODA re-analysis and the anti-cyclonic gyre in the northwestern Bay of Bengal during winter. The data further reveals an offshore front in January, which appears to be the result of a meso-scale re-circulation around an eddy, bringing cold and freshwater from the northern Bay of Bengal further away from the shore. Our cruise data hence illustrates that very strong salinity fronts can appear in the Bay of Bengal after the monsoon, as a result of intense coastal circulation and stirring by eddies.

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Evaluation of the national strong motion network in Greece: deployment,data-processing and site characterization     

B. Margaris  I. Kalogeras  Ch. Papaioannou  A. Savvaidis  N. Theodoulidis 《Bulletin of Earthquake Engineering》2014,12(1):237-254

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Floodplain construction by recent,rapid vertical accretion: Waipaoa River,New Zealand     

Basil Gomez  Dennis N. Eden  David H. Peacock  Edward J. Pinkney 《地球表面变化过程与地形》1998,23(5):405-413

The rate of vertical accretion (typically 14–18 mm h⁻¹) during eight floods in the Waipaoa River basin, with recurrence intervals of 5 to 60 years, was determined by relating the floodplain stratigraphy at McPhail's bend to the 1948–1995 flood history. Overbank deposits remaining after a flood that occurred in March 1996 suggest a rate of vertical accretion of 15 mm h⁻¹. By contrast, because the flow velocity across the floodplain was too high to permit deposition from suspension, during the record flood of March 1988 the rate of vertical accretion was only 6 mm h⁻¹. The sequence of deposition is highly discontinuous, and the rapid vertical accretion is a response to a late 19th to early 20th century phase of deforestation in the headwaters that probably initiated a far greater change in suspended sediment yield than in discharge. Cross-section surveys conducted since 1948 indicate that the high suspended sediment load of the Waipaoa River also promoted in-channel deposition, which effected a progressive reduction in bankfull channel width although, due to the overbank deposition, channel capacity remained constant. © 1998 John Wiley & Sons, Ltd.  相似文献   

Seismic hazard assessment and design spectra for the Kozani-Grevena region (Greece) after the earthquake of May 13, 1995     

N. Theodulidis  V. Lekidis  B. Margaris  C. Papazachos  Ch. Papaioannou  P. Dimitriu 《Journal of Geodynamics》1998,26(2-4)

The Kozani-Grevena (Greece) destructive earthquake occurred in a region of low seismicity. A considerable amount of strong-motion data was acquired from the permanent strong motion network of the Institute of Engineering Scismology and Earthquake Engineering (ITSAK) as well as from a temporary one installed after the earthquake. On the basis of this data set as well as on the observed macroseismic intensities, local attenuation relations for peak ground acceleration and velocity are proposed. A posteriori seismic hazard analysis is attempted for the affected and surrounding areas in terms of peak ground acceleration, velocity, bracketed duration and spectral acceleration. The analysis shows that the event of May 13, 1995 can be characterized as one with a mean return period of 500 to 1000 years. Relying on the observed spectral-acceleration amplification factors and the expected peak ground acceleration for mean return period of 500 years, region-specific elastic design spectra for the buildings of the Kozani and Grevena prefectures are proposed.  相似文献   

On the reliability of different methods of seismic hazard assessment in Greece     

B. C. Papazachos  Ch. A. Papaioannov  D. J. Papastamatiou  B. N. Margaris  N. P. Theodulidis 《Natural Hazards》1990,3(2):141-151

Historical and present century instrumental data have been used to determine seismic hazard in 35 sites of Greece by the application of Cornell's method (Cornell, 1968) and the mean value method. The macroseismic intensity has been considered as a measure of seismic hazard. Comparison of the results of the two methods showed that, in general, the mean value method gives higher values, particularly for low probabilities of exceedance. In addition, for some sites, the differences of the expected intensities resulting from the two methods, indicate that finer tuning of the seismogenic souce model is required, or suggest time dependence. Although each one of these methods has its own merits, the method based on seismic zonation (Cornell's method) has several advantages and must be preferred when an accurate zonation is possible by the use of macroseismic and instrumental seismic data, together with geological and geomorphological information. However, reliable estimates of seismic hazard at a particular site require work on a microzoning scale, incorporating historical, archaeological, and recent geological data.Paper presented at the 21st General Assembly of the European Seismological Commission held in Sofia, 1988.  相似文献   

Displacement spectra and displacement modification factors,based on records from Greece     

C.J. Athanassiadou  C.Z. Karakostas  B.N. Margaris  A.J. Kappos 《Soil Dynamics and Earthquake Engineering》2011

Elastic and inelastic displacement spectra (for periods up to 4.0 s) are derived, using a representative sample of acceleration records from Greece, carefully selected based on magnitude, distance and peak ground acceleration criteria, and grouped into three ground type categories according to the Eurocode 8 (EC8) provisions. The modification factor for the elastic design spectrum adopted in EC8 for accounting for damping is verified herein and is found to be satisfactory in the short to medium period range and less so in the long period range. The equivalent viscous damping ratio concept is also evaluated and is found to lead to underestimation of inelastic displacement spectra. Finally, based on the previously derived elastic and inelastic spectra, equations suitable for design and/or assessment purposes, are proposed for the corresponding displacement modification factors.  相似文献