846113 Anisotropic model of the earth's crust in the Baikal rift zone Maslova, S I; Obolentseva, I R Geophys d R Astr Sac V76, N1, Jan 1984, P227-232 (Paper to the Proceedings of the 1st International Workshop on Seismic Anisotropy, Suzdal, 11-19 May 1982)

An attempt is made to explain the existence of intracrustal low velocity layers in rift zones by using an anisotropic model. It is supposed that the anisotropy is due to the preferred orientation of micas and amphiboles in metamorphic rocks forming the up- per crust. Analysing the velocity distribution along different directions in anisotropic media, it is concluded that the low- velocity layer must be isotropic (randomly oriented) with an anisotropic lid.

846114 On the inversion of Love- and Rayleigh-wave dispersion and implications for earth structure and anisotropy Mitchell, B J Geophys 1 R Astr Soc V76, N1, Jan 1984, P233-241 (Paper to the Proceedings of the 1st International Workshop on Seismic Anisotropy, Suzdal, 11-19 May 1982)

It is suggested that the inability to explain both Love- and Rayleigh-wave dispersion data with relatively simple isotropic models can be caused by a number of factors other than that of intrinsic anisotropy; these include systematic errors in velocity measurement, lateral variations in structure and the use ofover- simplified starting models in the inversion process. Love/Rayleigh incompatibility is the term used and this can be removed if inversions are performed using isotropic models consisting of several thin layers.

846115 Anisotropy in the oceanic lithosphere of the North-western Pacific Basin Shimamura, H Geophys J R Astr Soc V76, N1, Jan 1984, P253-260 (Paper to the Proceedings of the 1st International Workshop on Seismic Anisotropy, Suzdal, 11-19 May 1982)

A series of long-range seismological experiments has been con- ducted using ocean bottom seismographs (OBS) in the western Pacific. These show that large-scale P-wave anisotropy exists in the entire thickness of the oceanic lithosphere. Analysis of seis- mic body waves suggests that the anisotropy has been 'frozen' at least since the change of plate motion 40M years ago.

846116 Anisotropy of ultrasonic seismic velocities and periods in a zone of tectonic disturbance Silaeva, O I Geophys J R Astr Soc V76, N1. Jan 1984, P261-268 (Paper to the Proceedings of the 1st International Workshop on Seismic Anisotropy, Suzdal, 11-19 May 1982)

Measurements were made of the velocity and period of ul- trasonic waves in situ in the zone of Karaswisk overthrust near the Toktogul hydroelectric station. These measurements revealed that the velocity and period anisotropies are dependent on the state of stress of the rock massif. Auth.

846117 Crustal structure beneath southern England from deep seismic reflection profiles Chadwick, R A; Kenolty, N; Whittaker, A d Geol Sac London VI40, N6, Not' 1983, P893-912

Seismic reflection events from profiles in southern England are interpreted in terms of stratigraphic and structural interfaces between rock units. Evidence is presented that a series of reflec- tion events, dipping between 22 degrees and 27 degrees, with

219A

azimuth averaging 160 degrees represents two major thrust zones occurring in the Variscan floor beneath Mesozoic cover. A geological model based upon borehole information and re- gional geological considerations is presented.

846118 Thickness of weathered mantle in Piedmont: variability and survey techniques Segovia, A V Transp Res Rec N919. 1983. P16-20

Variations in thickness of the weathered mantle at specific sites are difficult to predict on the basis of regional models of weathering for the Piedmont. Detection of fracture zones is sug- gested since they can cause sharp variations in overburden thickness over short distances because they tend to localize water percolation and increase depth ofweathering. Methods of detecting these fracture zones include aerial photography and use of geophysical field techniques.

T e c t o n i c processes

846119 Evaluation of criteria to deduce the sense of movement in sheared rocks Simpson, C; Schmid, S M Bull Geoi Soc Am 1/94, NIl, Nor 1983. P1281-1288

Some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking. Apparently conflicting evidence from rotated pressure-shadow regions around porphyroclasts is clarified. The use of quartz-crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations. Auth. 43 refs.

846120 Optical anisotropy of coals as an indicator of tectonic defor- mation, Broad Top Coal Field, Pennsylvania Levine. J R; Davis. A Bull Geol Soc Am 1/95, N1. Jan 1984. PI00-108

846121 Anisotropy: a pervasive feature of fault zones? Evans, g Geophys J R Astr Soe V76, N1. Jan 1984, P157-163 (Paper to the Proceedings of the 1st International Workshop on Seismic Anisotropy, Suzdal. 11-19 May 1982)

Current models of the structure of an active fault zone recognize two important subdivisions - an upper zone, extending to mid- crustal depths, in which processes associated with brittle frac- ture and friction dominate the fault behaviour, and a lower zone, extending into the mantle, within which stresses may be relieved by ductile flow. Anisotropy directly or indirectly in- duced by stress might occur throughout the fault zone, espe- cially if caused by some form of stress-induced crack alignment. Dilatancy associated with high stresses is likely to be a very localized phenomenon in the vicinity of high strength regions (asperities), but alignments caused by subcritical crack growth at low stress and strain rate (extensive-dilatancy anisotropy) could give rise to anisotropy throughout the fault region. Auth. 44 refs.