Eduard Berg

Correlation of foreshocks and aftershocks and asperities

A close correlation in spatial distribution of local seismic activity and energy release patterns before and after the 1979 Petatlan, Mexico earthquake suggests heterogeneity within the fault plane of this major low-angle thrust event associated with subduction along the Middle America Trench. A simple two-asperity model is proposed to account for the complexity. Foreshocks and aftershocks of the neighboring 1981 Playa Azul earthquake showed a similar pattern. As both events occurred at the junction of the Orozco Fracture Zone and the Middle America Trench, we speculate that the observed complex fault plane is caused by subduction of the rugged ocean floor of the Orozco Fracture Zone. Short-term precursory seismicity prior to the Petatlan earthquake can be explained by using the asperity model and migration of a slip front from the south-east to the north-west across the main shock source region.

Dynamic interaction of seismic activity along rising and sinking edges of plate boundaries

Abstract Cumulative and differential cumulative seismic strain release of shallow earthquakes during 1964 through 1972 show significant time-delayed correlation for many of the rises and/or sinks of tectonic plate boundaries for the Atlantic, Indian and Pacific oceans. For the Pacific, time delays are almost exclusively from areas of higher to areas of lower strain release, and could imply viscous stress relaxation along or near the lithosphere—asthenosphere boundary. Seismically determined slip rates for many of the subduction zones during 1964–1972 are lower than those of the preceding part of the century by a factor of 5. The significant correlation between many rises and sinks suggests worldwide interaction and coupling of plate motion.

Convergent Genetic Algorithm For Inversion

A genetic algorithm shown last year finds the global maximum of correlation tyfrc functions when many near equal maxima arc present. It conserves al1 genetic material of the starting population in successive gcneralions and convcrgcs as long as the population size is of the order of the chromosome length The algorithm was tested on a 10 parameter function with approximately 106 peaks ranging in their peak amplitude from 1 to 1.582. The function values ranged from 0 to the maximum peak. Figure I shows a two parameter version. here WC present detailed proper&s, an extension for faster convergence and conditions for convergcncc easily monitored during processing.

The Deformational Environment of the Haleakala Lunar Laser Ranging Observatory

The University of Hawaii is initiating a geodetic- geophysical program in support of the Lunar Laser Ranging at Haleakala, Maui, Hawaii. The program is aimed at measuring and understanding possible motion of the observatory site with respect to its surroundings, so that local and regional movement can be separated from the more general plate motion, as referred to other lunar ranging or VLBI stations.