Magnetar is a type of neutron star with extremely powerful magnetic field. They have mass of massive stars but compressed in small size about 6 miles across. They are one of the extreme objects in the universe. They are some neutron star which spins 1000 times per second. They have intense magnetic field.
Neutron stars have solid crust made of pure neutrons. It's crust is like a massive crystal and it is in huge stress because of extreme magnetic field. That stress can cause the surface to crack. The crust may have move very small amount but because Magnetar is so massive the energy which is released are enormous. It is beyond human imagination.
The most powerful earthquake measured on Earth was about 9 in Richter scale. Magnetrur can produce seismic event 32 on Richter scale. That is million times powerful than largest quakes on earth.
In 2004 scientists detected such a quake from Magnetar 50th light-years away. Its gamma ray crashes into earth magnetic field. Even though it was half way across the galaxy, it was able to compress Earth's magnetic field.