Foreshock One of a group of small to medium earthquakes which precede a large earthquake. At the time it can be difficult to know whether a cluster of earthquakes is predictive of a large eq. The Chinese prediction of a disastrous earthquake at Haicheng is one case where foreshocks were successfully identified and used to predict an earthquake. An oscillatory ground motion, observed by seismometers, which occurs as magma begins to move around in the understructure of a volcano, prior to eruption. Hazard A geological phenomenon or event which poses potential danger.
Risk is something different.
It lies directly below the epicenter, which is the surface location mapped for the eq. Lithosphere The outermost rocky shell of the earth, consisting of the crust and the uppermost mantle. It is cool enough that it resists being deformed. It forms a set of lithospheric plates, whose horizontal movements form the process of plate tectonics. Basalt The magma produced by partial melting of the rocks of the earth's mantle.