Abstract: The present method provides spatial sampling of a seismic wavefield on the free surface of the earth at an effective spatial sampling denser than the physical layout of the sensors. The sensors are comprised of a sensing element for vertical particle motion at the earth's surface, and a sensing element for rotational motion around a horizontal axis at the surface of the earth. Stress and wavefield conditions known at the free surface of the earth allow the rotational sensing element to yield the transverse horizontal gradient of the vertical particle motion wavefield. This horizontal gradient and the vertical particle motion data are utilized in the technique of ordinate and slope sampling to yield an improved transverse spatial sampling of the vertical particle motion wavefield. The method has a wide range of application in seismic surveys in oil and gas exploration and production.

Abstract: Subterranean mineral deposits, such as oil shale or the like, are prepared for in-situ retorting by selectively mining out an area at the base of the deposit leaving an overlying deposit supported in a suitable manner such as by a plurality of pillars. The overlying deposit is expanded in any suitable manner into the underlying area in a fashion to create a predetermined distribution of permeability from an area of low permeability to an area of high permeability. An inlet is provided at the low permeability area and an outlet at the high permeability area. A suitable medium is introduced into the deposit at the low permeability end for extracting and forcing mineral values from the deposit toward the outlet end for recovery.

Abstract: Subterranean mineral deposits, such as oil shale or the like, are prepared for in situ retorting by selectively mining out an area at the base of the deposit leaving an overlying deposit supported in a suitable manner such as by a plurality of pillars. The overlying deposit is expanded in any suitable manner into the underlying area in a fashion to create a predetermined distribution of permeability from an area of low permeability to an area of high permeability. An inlet is provided at the low permeability area and an outlet at the high permeability area. A suitable medium is introduced into the deposit at the low permeability end for extracting and forcing mineral values from the deposit toward the outlet end for recovery. .Iadd.