OLR fl'9g'~) 34 (1 l) D. Submarine Geology and Geophysics 969

decoupled from Sm-Nd, U-Pb, and Th-Pb frac- tionation. Small isotopic variations occurring on regional scales of 1-100 km are of lesser amplitude than those observed on large scales. On regional scales Pb isotope ratios are more highly correlated than in Pacific MORB overall and may record the age of events that created t h e regional mantle heterogeneities. Available data do not support the relationship of isotopic diversity and mean isotopic composition to spreading rate. Dept. of Geol. Sci., Cornell Univ., Ithaca, NY 17853-1504, USA.

87:6358 Wright, T.L. and R.T. Helz, 1987. Recent advances in

Hawaiian petrology and geochemistry. Prof. Pap. U.S. geol. Surv., 1350:625-640.

Active volcanism at Kilauea Volcano has provided natural laboratories to study the cooling, crystal- lization, and differentiation of basaltic magma which has resulted in the recognition of new petrologic processes, including storage of mantle-derived magma batches and mixing of these batches with magma stored and fractionated in rift zones. De- tailed study of the recently discovered Loihi Sea- mount has revealed a preshield alkalic stage similar to postshield alkalic stages. Stratigraphic studies of individual volcanoes show the diversity of chemical evolution of volcanoes in the chain, and combined isotopic and chemical data reveal significant com- plexity in the source mantle. The origin of Hawaiian magma, as defined by depth and degree of partial melting, enriched vs depleted sources, and miner- alogy of source mantle, is unresolved. Includes ca. 100 references.

D290. Crust, mantle, core

87:6359 Abe, Katsuyuki, 1987. Seismieity of Japan: earth-

quakes and tsunamis. [Overview.] Impact Sci. Soc., 145:63-74.

Japan and its environs are a typical island arc system in which the oceanic plates subduct on their way back into the mantle. Both shallow and deep earthquakes occur there, and many set off tsunamis. Japan has one of the longest histories of recorded earthquake activity in the world. A close exami- nation of the characteristics of its seismicity reveals some interesting features. Earthquake Res. Inst., Univ. of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan.

87:6360 Behrendt, J.C. and Annette Yuan, 1987. The Helena

Banks strike--slip (?) fault zone in the Charleston, South Carolina, earthquake area. Results from a marine, high-resolution, multichannel, seismic- reflection survey. Geol. Soc. Am. Bull., 98(5): 591-601.

The results of a high-resolution, multi-channel seismic reflection survey offshore of Charleston, South Carolina, indicate the Helena Banks fault zone (HBFZ) trends N66°E for ~110 km and consists of several left-stepping en echelon 10-40 km long segments suggestive of left-lateral strike-slip movement. Survey lines across the HBFZ indicate a displacement of 68 _+ 13 m on the J reflector (Jurassic basalt layer surface) and a 51_ 12 m/km increase with depth. Deep-penetration profiles identify the HBFZ as a reactivated boundary fault of the underlying narrow Kiawah Triassic (?) basin. USGS, Denver, CO 80225, USA. (hbf)

87:6361 Campbell, W.H. (ed.), 1987. Electrical properties of

the Earth's mantle. Special issue. Pure appl. Geophys., 125(2-3):193-497; 15 papers.

This collection of papers 'representative of recent international efforts to understand the electrical properties of the Earth's mantle,' is introduced by an article presenting an overview of current knowledge on the mantle--its characteristics, seismic investi- gations, observed electrical properties, and methods of investigation. A table and eight figures showing fifty model profiles summarize some published conductivity results on a common scale display. The profiles indicate agreement within an order of magnitude on the general level of conductivity for the mantle and provide evidence of heterogeneous electrical structure within the uppermost mantle. Other presentations review relevant seismic prop- erties, interrelations between mantle conductivity and other basic properties, conductivity modelling methods, and various research programs. (hbf)

87:6362 Clowes, Ron, 1987. LITHOPROBE: exploring the

snbdnction zone of western Canada. Leading Edge, 6(6): 12-19.

Southern Vancouver Island was selected as the focus for the 1984 phase I of this Canadian program planned to investigate the rigid outer 100 km of the Earth. The area was selected because it is a region of complex accreted terranes being underthrust by the subducting oceanic Juan de Fuca Plate where reconnaissance information, maps, and profiles are already available. CDP reflection profiles, supple-

b

970 D. Submarine Geology and Geophysics OLR ( 19~.7)'.M ~ 11 )

mented by seismic refraction, magnetotelluric and gravity data, paleomagnetic studies, radioactive isotope geochronology, and high precision chemical and mineral analyses, provide the basis for a detailed cross section of lithospheric structure. Preliminary results of a supplementary offshore CDP reflection survey support the general interpretation presented, but reveal that the top of the subducting plate lies somewhat lower than previously supposed. Univ. of British Columbia, Vancouver, Canada. (hbf)

87:6363 Dragert, H., 1987. The fall (and rise) of central

Vancouver Island: 1930-1985. Can. J. Earth Sci., 24(4):689-697.

Levelled height differences from first-order vertical control surveys between 1930 and 1984 indicate large apparent elevation changes along the east coast of central Vancouver Island, British Columbia. The survey following the 1946 earthquake (M = 7.3) indicated relative subsidence of up to 80 mm for the northern third of a 130 km traverse. Subsequent surveys indicated uplifts at rates of 1 mm/yr (1946-1977) and 5 mm/yr (1977-1984). Minimal estimates of tilting across central Vancouver Island indicate a possible average uplift rate of 1-2 mm/yr for the east coast with respect to the outer coast (1976-1985). These data are consistent with the sequence expected for an earthquake cycle--co- seismic subsidence followed by gradual postseismic recovery totalling 30 mm over 30 yr. The apparent recent acceleration of uplift could mark a stage of more rapid strain prior to a seismic event. Pacific Geosci. Centre, Dept. of Energy, Mines and Resour., P.O. Box 6000, Sidney, BC, V8L 4B2, Canada.

87:6364 Eissler, H.K. and Hiroo Kanamori, 1987. A single-

force model for the 1975 Kalapana, Hawaii, earthquake. J. geophys. Res., 92(B6):4827-4836. Scripps Inst. of Oceanogr., La Jolla, CA 92093, USA.

87:6365 Kogan, L.I., 1987. Structural inhomogeneities of the

consolidated seafloor crust. Dokl. Earth Sci. Sect. (a translation of Dokl. Akad. Nauk SSSR), 283(1-6):1-3.

New multichannel seismic reflection profiling data show the internal structure of consolidated oceanic crust is more complex than expected from results of deep seismic sounding. An upper layer is best modeled as one of lenses forming a unit 1.5-2.0 km thick; the middle interval, 5-7 km deep, consists of blocks of poor acoustic contrast bounded by zones of subvertical and vertical faults. The third structural

unit is best represented by a block and layer model. Comparison of the seismic data with data from deep sea drilling and dredging suggests the top interval reflects the distribution of acoustic inhomogeneities at the boundaries of lava flows, the second repre- sents vertical and subvertical inhomogeneities of a dike complex, and the third interval represents the root of the mantle or the base of the dike complex. Southern Div., Shirshov Inst. of Oceanol., Acad. of Sci., Gelendzhik, USSR.

87:6366 Kubas, Agnieszka and S.A. Sipkin, 1987. Non-

deuble-conple earthquake mechanisms in the Nazca Plate subduction zone. Geophys. Res. Lefts, 14(4):339-342.

Earthquakes occurring within the Nazca Plate subduction zone fall into two populations: generally smaller, nearly pure double-couple events, and usually larger, non-double-couple earthquakes. There appears a direct relationship between the proportion of the non-double-couple component in the earthquake solution and the scalar moment, a trend not observed on the global scale. Most earthquakes with large non-double-couple compo- nents occur where the greatest amount of structural complexity is expected. We hypothesize that non- double-couple mechanisms in this region are related to the breakdown of the assumption of slip on a planar fault surface, one of the fundamental as- sumptions in obtaining moment tensor source mechanisms in accord with the double-couple model. This failure is related to extreme structural complexity in this region. Inst. Francais du Petrole, Paris, France.

87:6367 Kuznetsov, O.L., 1987. Deep continental drilling on

the Kola Peninsula and the structure of the Earth's crust. [Overview.] Impact Sci. Soc., 145: 89-96.

In the Soviet Union an integrated program using geographical, geophysical and geochemical methods and new deep drilling techniques is being used to study processes in the crust and upper mantle. The first drilling, on the fringe of the Baltic Shield, has thrown" new light on the evolution and structure of early continental crust, c /o USSR Comm. for Unesco, Ministry of Foreign Affairs, 9, Prospekt Kalinina, Moscow G-19, USSR.

87:6368 Minster, J.B. and T.H. Jordan, 1987. Vector can-

straints on western U.S. deformation from space geodesy, neotectonics, and plate motions. J. geophys. Res., 92(B6):4798-4804.