This article presents a tutorial of the bases for, and problems encountered with, the resistivity and induced polarization methods in geotechnical and environmental applications. It commences with a discussion of aqueous electrolytic conduction in rocks including consideration of the effects of temperature, rock texture, rock type, geological processes, and of the presence of clay minerals. Both electrode and membrane polarization in soils and rocks are described.The elementary theory for the resistivity and induced polarization methods is introduced via formulas for electrodes on homogeneous and layered half-spaces. The notion of apparent resistivity is presented. Vertical electric sounding is described in relation to curve types, inversion, equivalence, anisotropy, and correlation. Profiling with resistivity is briefly treated while combined sounding-profiling is treated in more detail for both the resistivity and induced polarization methods. The parameters used to describe the induced polarization phenomena are introduced. A brief discourse follows on data acquisition and processing, including design considerations for transmitters and receivers, electrodes, and wire logistics.A section on arrays and the factors involved in selecting an array provokes the disclosure that while their application in geotechnical and environmental studies usually is straightforward much remains to be learned about the resistivity and induced polarization methods in general. Specific topics requiring study are comparative studies of various arrays in (a) depth of exploration in sounding and in profiling, (b) resolution of horizontal structures, (c) sensitivity to depth, (d) sensitivity to lateral effects, (e) sensitivity to buried and surface topography, and (f) the effectiveness of focused arrays.References to recent significant publications on one-, two-, and three-dimensional forward and inverse interpretation procedures follow. Problems encountered with these methods are initially treated under the section on arrays and are expanded with specific reference to geologic noise and negative induced polarization effects. The advantages of focused arrays are illustrated.The paper concludes with nine representative examples of applications. IntroductionBulk resistivities from the surface to more than 15 km depth in a normal crust are controlled by aqueous electrolytic conduction by way of pores, fractures, faults, and shear zones. The regime of primary interest in this article is significantly less than 15 km and is often less than 5 m. A slight increase in resistivity with depth in this 0-15 km region is the result of decreasing pore, fracture, fault, and shear-zone porosity due to increased lithostatic load. It is well to keep in mind, however, that fractures and faults are known to remain open to depths in excess of 15 km due to departures from lithostatic loading whenever the major component of the stress tensor is other than vertical. I draw attention to this latter fact because of the need to observe it when considering, for e...

It is my sincere desire that the data herein presented will overtake and cancel the unjust consequences of misinformation. NATURE OF PREDICTIONS The following quotation of statements made by Dr. Willis will make clear the nature of his prophecies. "Indications are that we may anticipate a grave, farreaching quake in Southern California." "A great shock may come soon or within a decade, or not until after more than a decade." "The indications are that we have to expect a deepseated, more far-reaching earthquake in Southern SOUTHERN CALIFORNIA ATTACKED 5 California. In the north we have quite a long period to wait." "These conditions may be interpreted as indicating either little chance of earthquake in Los Angeles and vicinity, or the probability of a severe shock in the not distant future, the latter alternative being of the PART TWO GENERALIZATIONS CONCERNING EARTHQUAKES This paper is not a treatise on the general subject of earthquakes, and hence I discuss the subject only briefly. Volumes have been written about them and the reader who wishes to delve more deeply into the subject can find many books to satisfy his thirst for knowledge.M odern seismologists hold that an ordinary earthquake is a deep-seated jar to the earth's crust caused when the rock suddenly moves, snaps back, or elastically recoils as a result of release from strain. This is called the rebound theory. In harmony with it, Dr. Daly defines an earthquake as a "snap." Such releases of strains are usually local occurrences, which are associated with earth cracks shown as "faults" or "fault lines," and occur at spots along their extent.

débris of the Burnet granite. They also vary in composition and thickness with the irregularities of the floor.West of the 98th meridian the Trinity sands are deposited unconformably upon the various beds of the " Triassic," or gypsiferous red beds, as seen * In places these pebbles are cemented into large masses of conglomerate, as at San Angelo, in Tom Green county, where it attains a great thickness and areal development.

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