Theoretical amplitudes of body waves from a dislocation source in the Earth II. Core phases     

Michael Shimshoni  Yehuda Sylman  Ari Ben-Menahem 《Physics of the Earth and Planetary Interiors》1973,7(1):59-91

Expressions are obtained for the ray-theoretical spectral amplitudes of body waves induced by a shear dislocation of arbitrary orientation and depth situated in a radially heterogeneous model of the earth. Account is taken of the azimuthal and colatitudinal radiation patterns of the source, the geometrical spreading, and the reflections and refractions at the free surface and at the mantle-core boundary.In this work spectral amplitudes are calculated for PKP, PKS, SKP and SKS. The results are presented in the form of tables for a source of strength U₀dS = 10¹⁵ cm³, where U₀ is the amount of the dislocation and dS is the fault area. Given the slip and dip angles of the source, the amplitudes of the four core phases can be obtained from these tables for all azimuths, for most of the epicentral distances at which a particular phase is observable, and for all the fourteen focal depths included in the Jeffreys-Bullen tables. It is found that the depth of the source has a strong effect on the amplitudes of the body-wave signals.  相似文献   

Earthquake similarity laws     

Ari Ben-Menahem 《Physics of the Earth and Planetary Interiors》1977,15(1):P10-P18

Source parameters of 27 major shallow earthquakes in the magnitude range 7.0–8.6, which occurred during 1906–1969, are used to establish dimensionless invariants involving the fault dimensions, average slip, and the rise time. It is found that these entities are expressible as simple functions of the subsonic shear Mach number (M) and the cube root of the seismic potency, $\text{(}\text{U}\text{S)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$. Moreover, a new principle is suggested according to which all dimensionless numbers which can be constructed from the basic fault elements are simple powers of the contraction factor $\text{(1-M}{}^2\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ with coefficients of the order unity. The laws of dynamical similarity thus found are those appropriate for subsonic rupture in which the Mach number is very close to unity and the radiation efficiency is between $\text{1}\text{6}$ and $\text{1}\text{3}$. The empirical similarity laws are shown to be compatible with a source model in which the fault plane is simulated by a flexible membrane with additional restoring stiffness forces provided by an elastic medium attached to it on one side. Results suggest the possibility that earthquake rupture, together with the radiation of seismic waves, terminates at the moment that Mach 1 is reached.  相似文献   

Rate of seismicity of the dead sea region over the past 4000 years     

Ari Ben-Menahem  Ezra Aboodi  Moshe Vered  Robert L. Kovach 《Physics of the Earth and Planetary Interiors》1977,14(4):P17-P27

The results of two millennia of earthquake documentation, a few decades of macroseismic and instrumental routine seismological observations and five months of microearthquake monitoring, are used to estimate the rate of seismic activity of the Dead Sea fault. It is found that these vastly diverse data which combine long- and short-term tectonic processes, are in good accord with the formula: where N is the annual number of events of local magnitude M_L or greater. If this equation is extrapolated to ca. 2000 B.C., it yields a Richter magnitude M_s = 7 for the event of Sodom and Gomorrah which is believed to be associated with the strongest earthquake in the region during historical times.Comparing our findings with the results of other investigators in Turkey, Greece, Aegean Sea and Iran, we note that the b values along the Syrian-African rift zone (0.78–0.86) are smaller than those in Greece and its surrounding seas (0.94–1.16).  相似文献   

Theoretical amplitudes of body waves from a dislocation source in the earth III. P,S and surface reflections     

Yehuda Sylman  Michael Shimshoni  Ari Ben-Menahem 《Physics of the Earth and Planetary Interiors》1974,8(2):130-147

Expressions are obtained for the ray-theoretical spectral amplitudes of body waves induced by a shear dislocation of arbitrary orientation and depth situated in a radially heterogeneous model of the earth. Account is taken of the azimuthal and colatitudinal radiation patterns of the source, the geometrical spreading, and the reflections and refractions at the free surface and at the mantle-core boundary.In this work spectral amplitudes are calculated for P, SH, SV, PP, PPP, PS, PSS, SP, SPP, SSH, SSSH, SSV, and SSSV. The results are presented in the form of tables for a source of strength U₀dS = 10¹⁵cm³, where U₀ is the amount of the dislocation and dS is the fault area. Given the slip and dip angles of the source, the amplitudes of these surface reflections and direct phases can be obtained from these tables for all azimuths, for most of the epicentral distances at which a particular phase is observable, and for all the fourteen focal depths included in the Jeffreys-Bullen tables. It is found that the depth of the source has a strong effect on the amplitudes of the body wave signals.  相似文献   

Satellite image based vegetation classification of a large area using limited ground reference data: a case study in the Usa Basin, north-east European Russia     

Tarmo Virtanen  Kari Mikkola  Ari Nikula 《Polar research》2004,23(1):51-66

Predicted global changes can be studied effectively by combining spatially explicit data sets on vegetation and other landscape properties with process models. However, detailed knowledge of the vegetation distribution of remote Arctic areas is relatively scarce. This paper shows how a mesoscale vegetation and land cover classification of a large, remote Arctic area can be conducted at a fine spatial resolution (30 m cell size) using a limited ground reference data set. The study area is the catchment of the River Usa (93 500 km²) in north-eastern European Russia. Vegetation zones in the Usa Basin range from taiga in the south to forest-tundra and tundra in the north, and to alpine in the Ural mountains in the east. Classification was done using a mosaic of spectrally adjusted Landsat TM5 images from five different dates and a semi-supervised method. Ground reference data were collected during the summers of 1998, 1999 and 2000. Accuracy of the 21-class vegetation type/land cover classification produced was tested against test points interpreted from oblique aerial photographs taken from a helicopter (logistic limitations prohibited the collection of representative ground reference data). The main vegetation types (forests, willow dominated stands and meadows, peatlands, tundra heaths, mainly unvegetated areas, and water bodies) were distinguished with relatively high accuracy: 84% of the test points were classified correctly. Spatially detailed land cover data sets like the one described here allow detailed landscape-level analysis and process modelling on many different subjects.  相似文献   

Using phytogeomorphology, cartography and GIS to explain forest site productivity expressed as tree height in southern and central Finland     

Timo Korkalainen  Ari Laurn 《Geomorphology》2006,74(1-4):271-284

Using geomorphological knowledge, spatial data and GIS methods, one can obtain phytogeomorphological site variables describing interactions between landforms and vegetation. We used 15 site variables derived from maps to explain forest site productivity in southern and central Finland expressed as dominant height of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) with ages of 30–110 years. These site variables were grouped into two: Group 1 with seven variables describing geographical conditions of sites including climate, and Group 2 with eight variables describing local morphometric and soil properties. We calculated slope and aspect from a 25 × 25 m DEM. The catchment area, calcium content in soil, length of the growing season, radiation index, sea index, lake index, past highest shoreline and total annual temperature sum with threshold + 5 °C were also obtained. Then we classified the landforms of 688 sample plots into four major types and 15 sub-types. We applied regression analysis to explain the tree height as a function of the tree age and the phytogeomorphological site variables. When the tree height was explained with the tree age and the Group 1 variables, the remaining standard error of the model was 16.6–17.9%. When the Group 2 variables were added to the analysis, the standard error decreased slightly. The most significant variables were the temperature sum, latitude coordinate and length of the growing season. Other significant variables were elevation, slope and aspect. The major landform types, sub-types and watershed area did not explain the tree height. Furthermore, if the forest site types determined in the field were included, the remaining standard error decreased by ca. 2%, showing the importance of field information.  相似文献   

Vector-scattering of elastic waves by directional structural space gradients     

Ari Ben-Menahem 《Pure and Applied Geophysics》1988,128(1-2):133-146

A nonstochastic and noniterative theory of vector scattering in inhomogeneous media is presented. The elastodynamic vector wave-equation for 3D inhomogeneous media is solved for a weak heterogeneity at the high-frequency region. It is shown that there exists a forward scattered field which decays slowly along the source-receiver path. Its rate of attenuation depends on the azimuth of the path relative to the direction of the inhomogeneity, but is independent of frequency. The Green's tensor for the above regime is derived in closed form and leads to the quantification of fields of dipolar sources in weak inhomogeneous media. The inhomogeneity at the source creates a source-induced scattering (in addition to path-scattering) having a radiation-pattern that bears the signature of the source. The availability of the analytic Green's tensor, in conjunction with the Huygens-Kirchhoff-Helmholtz formalism, opens new ways to calculate the scattered fields due to various structural inhomogeneities applicable to exploration and earthquake seismology. The theoretical results of this study point to the conclusion that the scalar wave approximation may not always be valid for the propagation of seismic waves in the earth's lithosphere.  相似文献   

Petrology of Serra Geral (Paraná) continental flood basalts,southern Brazil: crustal contamination,source material,and South Atlantic magmatism     

R. V. Fodor  Cricket Corwin  Ari Roisenberg 《Contributions to Mineralogy and Petrology》1985,91(1):54-65

The Serra Geral (Paraná) continental flood basalt (SG-CFB) province in Brazil is associated with the Jurassic-Cretaceous breakup of Gondwanaland and the transition of continental to oceanic magmatism during the opening of the South Atlantic Ocean. A suite of 24 samples representative of the SG-CFB in Rio Grande do Sul, southern Brazil, shows a compositional continuum from basalt (50–53 wt% SiO₂, Mg# 60-45), to basaltic andesite, to andesite, rhyodacite, and rhyolite (73 wt% SiO₂). Certain compositional aspects of the mafic rocks (e.g., TiO₂, K₂O, CaO, Zr/Nb, Zr/Y, Ti/Zr) resemble those of basaltic dikes and flows associated with the opening of the North Atlantic Ocean.Fractionation trends are apparent in MgO variation diagrams and calculations show that basalt-basaltic andesite continuums are largely due to removal of plagioclase and clinopyroxene. These mafic rocks can be categorized as (i) having higher or lower incompatible-element contents (e.g. K₂O 0.6–1.5 wt%; Rb 12–43 ppm; Ba 125–240 ppm) due to incorporation of Brazilian Archean crust or rhyolitic magma by basalt from a particular source material or to partial-melting differences of that source, and (ii) as having higher or lower TiO₂, Sr, Ba, and P contents due to source heterogeneities. Crustal components are obvious in certain basaltic samples, as where K₂O > 1 wt%, SiO₂ > 51%, and TiO₂ 1%, but are insignificant in others (e.g., compositions close to those of South Atlantic basin basalts). Calculations indicate origins for intermediate and silicic rocks by removal of pl, cpx, and Ti-magnetite from basaltic andesite, but crust and magma-mixing affecting basaltic-andesite fractionates were likely also involved. Where contamination is insignificant, Zr, Nb, and Y abundances indicate T-type MORE source material like that for certain S. Atlantic Ocean basalts. Source material was essentially a 91 hybrid of N-type and P-type MORB components. N-type MORB lithosphere followed SG-CFB because decompression due to rifting crust enabled partial melting of uppermost (depleted) mantle.  相似文献   

Complex exposure histories of chert clasts in the late Pleistocene shorelines of Lake Lisan,southern Israel     

Ari Matmon  Onn Crouvi  Yehouda Enzel  Paul Bierman  Jennifer Larsen  Naomi Porat  Rivka Amit  Marc Caffee 《地球表面变化过程与地形》2003,28(5):493-506

Activities of ²⁶Al and ¹⁰Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert‐bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio ²⁶Al/¹⁰Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP . If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My^?1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

A new derivation of the ratio Q(wobble)/Q_μ (mantle)     

Ari Ben-Menahem 《Geophysical Journal International》1982,70(2):535-537

Summary An extension of the Love-Larmor theory to a low-loss unelastic earth model, leads to the surprisingly simple approximation
   
where τ_s= 447.4 sidereal day is the static wobble period, τ_R= 306 sidereal day is the rigid-earth wobble period and τ_w= 433 sidereal day is the observed Chandler period. Q _W, Q _μ are the respective average Q values of the wobble and the Earth's mantle at τ_W. The known numerical factor F is only slightly dependent on the Earth structure.  相似文献