972 D. Submarine Geology and Geophysics OLR (1987) 34 ( I I')

87:6373 Rusakov, O.M., V.I. Starostenko and V.G. Koz-

lenko, 1987. Density inhomogeneities in the mantle responsible for planetary gravitational anomalies in the Indian Ocean. Dokl. Earth Sci. Sect. (a translation of Dokl. Akad. Nauk SSSR), 283(1-6):23-27.

A three-dimensional density model of the crust and mantle with a correction for the sphericity of the Earth shows that planetary gravitational anomalies within this area interfere with each other. The anomalies are induced by the combined effect of inhomogeneities of all layers of the mantle with a strong contribution by anomalies in the two topmost layers. The solution is sensitive to changes in the contours of anomalous masses and relatively insen- sitive to variations in the ratio of velocity inho- mogeneities to density inhomogeneities. Subbotin Inst. of Geophys., Ukrainian Acad. of Sci., Kiev, USSR.

87:6374 Savage, J.C., W.H. Prescott and M. Lisowski, 1987.

Deformation along the San Andreas Fault 1982- 1986 as indicated by frequent geodolite meas- urements. J. geophys. Res., 92(B6):4785-4797.

Measurements of six 3-line (10-40 km) strain networks located along the locked sections in southern and central California provide a time history of deformation. The standard error in measurement ranges from 0.4 ppm in line length for the shortest lines to 0.2 ppm for the longest lines. Except for one example of coseismic offset and postseismic relaxation the observations are at least marginally consistent with uniform-in-time defor- mation. The records of deformation at the networks closest to the epicenters of two recent magnitude 6 earthquakes (1984 Morgan Hill and 1986 North Palm Springs) were particularly stable in the year preceding the earthquakes. It is unlikely that these earthquakes were triggered by regional strain events. However, marginally significant anomalies were observed 12-18 months before both earthquakes. USGS, 345 Middlefield Rd., Menlo Park, CA 94025, USA.

87:6375 Solov'ev, S.L. and K.A. Kechekezyan, 1985. The

distribution of aftershock hypocenters and the seismotectonic process in the focal region of Kurilean earthquakes of March 22-24, 1978. Phys. solid Earth (a translation of Fiz. Zemli), 21(12):907-915. Shirshov Inst. of Oceanoi., Acad. of Sci., USSR.

87:6376 Spivack, A.J. and J.M. Edmond, 1987. Boron isotope

exchange between seawater and the oceanic crust. Geochim. cosmochim. A cta, 51 (5): 1033-1043.

The boron isotopic composition of seawater was redetermined and hydrothermal solutions and fresh and altered basalts were analyzed to help constrain a chemical and isotopic mass balance for B in seawater and oceanic crust. Dissolved B in Atlantic and Pacific seawater is isotopically homogeneous at 39.5 per rail; unaltered MORB from the crest of the EPR at 21 ° and 13°N have B contents of 0.39+0.03 and 0.46_+ 0.03 ppm (about one order of magnitude lower than previous estimates). Large scale B exchange between seawater and crust was demon- strated at both high and low temperature. Div. of Geolog. and Planetary Sci., Calif. Inst. of Tech., Pasadena, CA 91125, USA.

87:6377 Sverdrup, K.A., 1987. Multiple-event relocation of

earthquakes near the Gorda Rise-Mendocino Fracture Zone intersection. Geophys. Res. Letts, 14(4):347-350.

Earthquakes along the southern edge of the Gorda Plate and the Mendocino Fracture Zone that were relocated jointly generally move 25-35 km southwest of their PDE and ISC locations. This reduces the number of events occurring deep in the plate, increases the number of events located on the Gorda Rise, and reveals a tightly grouped linear zone of activity extending along the Mendocino Fracture Zone. The resulting spatial pattern of seismicity is more consistent with recent tectonic models of the area. Dept. of Geol. and Geophys. Sci., Univ. of Wisconsin, Milwaukee, WI, USA.

87:6378 Thatcher, Wayne and Michael Lisowski, 1987.

Long-term seismic potential of the San Andreas Fault southeast of San Francisco, California. J. geophys. Res., 92(B6):4771-4784.

Decade or longer seismic potential of the 125-km segment of the fault SE of San Francisco has been assessed by comparing the slip accompanying the 1906 earthquake with the slip deficit made up since. Of particular importance is the inconsistency be- tween 1906 surface offsets and geodetically deter- mined coseismic slip on the southern 90 km of the Peninsular San Andreas, a discrepancy not attrib- utable to large observational uncertainties or short- comings in fault modeling; the problem lies in the complexity of the fault (trend changes of 6 °, variable width, heavy vegetation and inaccessibility). To the northwest, maximum surface offsets were signifi-