Geoexplorution, 12(1974)185-234 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

Abstracts

(Revised version accepted for publication January 1974)

DEFORMATION OF PLATE EDGES IN CONTINENT--CONTINENT COLLISION

X. LE PICHON

Institute of Geophysics and Planetary Physics, University of California, San Diego, La Jolla, Calif. (U.S.A.)

Of the 2.6 km2 of plate surface destroyed each year on the earth, about 0.4 km2 are destroyed by continent-continent collision, in an as yet poorly understood manner, mainly along the alpine-himalayan system between Turkey and Burma. It is argued that the geological and geophysical evidence there indicates that the process of destruction of surface is not basically dif- ferent from the process of consumption of oceanic plates near trenches, in spite of the fact that it is much less efficient. The formation of the Indo- Gangetic and Mesopotamia sedimentary basins is interpreted within this con- text.

THE ACCURACY OF VELOCITIES FROM SEISMIC DATA

F.K. LEVIN, J.W. DUNKIN and y.ivi. SHAH

Esso Production Research Company, Houston, Texas (U.S.A.)

In the translation from seismograms to subsurface geology, the determina- tion of velocity directly from the recorded data is central. Modern velocity programs yield estimates of the arrival times and RMS velocities for the reflec- tions; from these quantities, interval velocities, average velocities, and depths to reflectors are computed.

To obtain estimates of the accuracy with which time, velocity, and depth can be found, we have conducted theoretical investigations. Starting with times which were randomly distributed around hyperbolic time-distance curves, we have found the first-order statistical properties of the several quan- tities. The theory predicts that travel time is overestimated and RMS velocity underestimated by the velocity programs, while interval velocity has zero mean but a large standard deviation.