770 D. Submarine Geology and Geophysics OI.R (1987) 34 (9)

Geophys. Inst., Faculty of Sci., Univ. of Tokyo, Tokyo 113, Japan. (hbf)

87:5116 Mandl, G., 1987. Discontinuous fault zones. J. struct.

Geol., 9(1): 105-110.

Many tectonic faults and tension fractures are, at least initially, composed of separate segments. A little explored reason for this phenomenon has implications both for the migration of hydrocarbons and for the sealing capacity of faults. Theoretical arguments based on Coulomb-Mohr 's theory of shear failure and on a theorem for the integrability of vector fields lead to the expectation that non- uniform 3-D stress fields will impede the formation of smooth, coherent fault surfaces; this is in contrast to stress fields associated with plane deformation. Koninklijke Shell Exploratie en Produktie Lab., Rijswijk, Netherlands.

87:5117 Morton, A.C. and P.N. Taylor, 1987. Lead isotope

evidence for the structure of the Rockall dipping- reflector passive margin. Nature, Lond., 326(6111):381-383.

These reflectors were sampled and proved to consist almost exclusively of basalt. Lead isotope data indicate that these basalts may have been contam- inated by ancient uranium-depleted continental crust, or alternatively, derived from a sub-conti- nental lithospheric mantle source. In either case, the implications are that the basalts formed by eruption through and onto continental basement, not by 'subaerial seafloor spreading.' This conclusion is in accord with gravity models of the area, which predict stretched continental crust beneath the dipping reflector sequence. British Geol. Survey, Keyworth, Nottingham NGI2 5GG, UK.

87:5118 Okal, E.A. and Seth Stein, 1987. The 1942 southwest

Indian Ocean Ridge earthquake: largest ever recorded on an oceanic transform. Geophys. Res. Lefts, 14(2): 147-150.

The 1942 southwest Indian Ocean earthquake is the largest ever recorded on an oceanic transform. Its mechanism has essentially the expected pure strike- slip geometry. Using long-period surface wave techniques, the seismic moment is found to be 1.3 x 1028 dyn-cm; directivity suggests southwest- ward rupture propagation over approximately 130 kin. This shock is then much smaller than previously reported on the basis of its high unified Richter magnitude (M--8.3). It does not show the slow energy release occasionally found in large transform fault events. Dept. of Geol. Sci., Northwestern Univ., Evanston, IL 60201, USA.

87:5119 Peacock, S.M., 1987. Serpentinization and infiltration

metasomatism in the Trinity peridotite, Klamath province, northern California: implications for subduction zones. Contr. Miner. Petrology, 95(1): 55-70. Dept. of Geol., Arizona State Univ., Tempe, AZ 85287, USA.

87:5120 Robinson, D. et al., 1987. Two-phase flow in crust

and mantle. J. geol. Soc., Lond., 144(2):257-348; 8 papers.

87:5121 Rundle, J.B. and Hiroo Kanamori, 1987. Application

o! an inhomogeneous stress (patch) model to complex subduction zone earthquakes. A discrete interaction matrix approach. J. geophys. Res., 92(B3):2606-2616.

In recent years it has been recognized that shear and normal stress along a fault can vary, and it has been suspected that faults might interact in some way. To explore these ideas an interaction matrix to express the influence of one fault upon another was developed which is calculated by using the energy change for a system of interacting cracks or faults and which relates the area-averaged stress on the fault segment to the area-averaged slip state on other fault segments in the system. The matrix method was then applied to a segment or 'patch' model for earthquakes in which each discrete fault segment has the same coseismic stress change each time it slips; results showed that both slip on a patch during an earthquake and the seismic moment produced by an earthquake on a set of patches can vary substan- tially. Earthquake sequences off the Colombia- Ecuador coast and the Nankai Trough near Japan were examined using these concepts. Div. 1541, Sandia Natl. Lab., Albuquerque, NM 87185, USA.

87:5122 Shirley, J.H., 1986. Lunar periodicity in great earth-

quakes, 1950-1965. Gerl. Beitr. Geophys., 95(6): 509-515.

The annual average worldwide seismic energy release from 1950-1965 was nearly two orders of magnitude larger than that during the period prior to 1950 or after 1965. A pattern is present in the timing of the 13 great earthquakes which comprise this major pulse. The series of lunar ecliptic longitudes for the occurrence times of these earthquakes shows both statistically significant clustering and an order- ly progression with time, suggesting that gravita- tional stresses may play a contributory role in triggering these great earthquakes. P.O. Box 169, Canoga Park, CA 91305, USA.