So far, in this book, we have modeled earthquake rupture by assuming a homogeneous isotropic infinite elastic body. However, the Earth has a ground surface, of course, and its existence should be taken into account when modeling fault slips near the ground surface. It is also well known that the Earth's interior, especially the crust, where most earthquakes are nucleated, forms a layered structure. Since large-size faults may cross these layer interfaces and even breach the ground surface, realistic modeling of large shallow earthquakes requires consideration of the layered structure with the ground surface.