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An interpretive map of the orientation of minimum horizontal stress for the contiguous United States, based on in situ stress measurements, geological data, and earthquake focal mechanism solutions, indicated that the state of stress within the plate is not uniform. The tectonically active western United States was shown to possess a complicated stress pattern, but even in the relatively quiet eastern and central parts of the country, several major variations in orientation of stress were apparent.

A new study, based on measurements in North America, Africa, and Australia, revealed that, on the average, maximum sheer stress increases linearly with depth to at least 5 km, with no indication of leveling off.