Are planet-destroying quakes possible or observable? The Gutenberg-Richter-Law is a very-well studied relationship between the magnitude and total number of (earth)quakes. In theory, there is no upper bound for the size of a quake other than the size of the planet. In other words: There is a non-zero probability (which is rather low) that a quake can rip appart the whole planet. There are numerical evidences with toy models such as the Olami–Feder–Christensen model suggest, such things can really happen.
Therefore my question: Are they any hints for (exo)planet-destroying quakes? And what about star-quakes which occur during stationary phases of star evolution?
References

cond-mat/0608324: Transient and stationary behavior of the Olami-Feder-Christensen earthquake model - not the publication which claims that planet-destroying quakes are possible, but a possible introduction to the kind of numerical methods used
A planet-ripping earthquake isn't possible on Earth.  For a magnitude 10.5 Richter scale earthquake, one would need twice the fault lines that exist on Earth according to the USGS.
The same website relates energy $E$ in joules to earthquake magnitude $M$ with Baths equation: $log E = 5.24 + 1.44M$.  A 10.5 magnitude earthquake would produce about 2.29e20 joules of energy.  The Earth's gravitational binding energy is about 2e32 joules. So if all possible earthquakes went off at the same time twice, it would only generate a trillionth of the energy necessary to rip the planet apart. Earthquakes occur just under the surface of the earth, and they release their energy over time. So, even if an earthquake could generate 2e32 joules of energy, it wouldn't be sufficiently directed to destroy the planet.
Earthquakes are the product of built up energy in tectonic plates by convecting magma.  This is a small effect compared to the power of gravity. The IAU requires a planet to have &quot;sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.&quot; That means gravity is a dominant force over the rigidity of the materials that compose the planet. But the seismic moment is governed by the modulus of rigidity of the materials. So localized earthquake forces and energies will be small compared to the gravitational forces from the planet itself.  So, we wouldn't expect planet ripping earthquakes on exo-planets either.
Notes:

If we consider nuclear fusion as a source of quakes, then supernovas might be called star-ripping quakes.

If we consider collisions as a source of quakes, then the asteroid 16 Psyche might be an example of a proto-planet destroyed by earthquakes.