Complex sentence: The seismic wave produced when the primary airburst's blast struck the ground yields a rather uncertain "best estimate" of 430 kilotons (momentum ignored), corresponding to the seismic wave which registered on seismographs at magnitude 2.7.
Split into simpler sentences: The seismic wave produced when the primary airburst's blast struck the ground yields a rather uncertain "best estimate" of 430 kilotons (momentum ignored). Corresponding to the seismic wave which registered on seismographs at magnitude 2.7.