Seismic magnitude scales by tectonic forces. When this stress becomes great enough to rupture the crust, or to overcome the friction that prevents one block of crust from slipping past another, energy is released, some of it in the form of various kinds of seismic waves that cause ground-shaking, or quaking. "Magnitude" is an estimate of the relative "size" or strength of an "earthquake", and thus its potential for causing ground-shaking. It is "approximately related to the released seismic energy." "Intensity" refers to the strength or force of "shaking" at a given location, and can be related to the peak ground velocity. With
Seismic tomography frame to compare tomographic models to for iteration. Initial models had resolution of ~3000 to 5000 km, as compared to the few hundred kilometer resolution of current models. Seismic tomographic models improve with advancements in computing and expansion of seismic networks. Recent models of global body waves used over 10 traveltimes to model 10 to 10 unknowns. Seismic tomography uses seismic records to create 2D and 3D images of subsurface anomalies by solving large inverse problems such that generate models consistent with observed data. Various methods are used to resolve anomalies in the crust and lithosphere, shallow mantle, whole mantle,