Crust (geology) centers, where partial-melting of the underlying mantle yields basaltic magmas and new ocean crust forms. This "ridge push" is one of the driving forces of plate tectonics, and it is constantly creating new ocean crust. That means that old crust must be destroyed somewhere, so, opposite a spreading center, there is usually a subduction zone: a trench where an ocean plate is being shoved back into the mantle. This constant process of creating new ocean crust and destroying old ocean crust means that the oldest ocean crust on Earth today is only about 200 million years old. In contrast, the
International Association for Engineering Geology and the Environment large projects and in the assessment and remediation of environmental issues, an update of the first statutes of the association was deemed necessary. The second statutes were approved by the general assembly in Kyoto (Japan) in 1992. A new definition of engineering geology was given, which reflected the experience collected during the previous 25 years and read as follows: "“Engineering geology is a science devoted to the investigation, study and solution of engineering and environmental problems which may arise as the result of the interaction between geology and the works and activities of man as well as to the prediction