 Focal mechanism

A description of earthquake source geometry, often strike, dip and rake for a double-couple shear fault. First-motion polarities constrain the radiation sign pattern, with a fundamental interchange ambiguity between fault and auxiliary planes.

Focal mechanism, also known as a fault mechanism or "beachball" diagram in seismology, refers to the orientation and movement along fault planes that cause an earthquake. It is a graphical representation that simplifies the complex three-dimensional motion of seismic waves generated by the rupture during an earthquake. The focal mechanism depicts the types of faulting that can occur, such as: 1. **Normal Faulting**: This occurs when the Earth's crust is extended.