split up vs sunder

split up

verb
  • separate, disassociate, cause to come apart. 

  • Cease to be together, break apart from the group. 

adj
  • Divided or separated. 

sunder

verb
  • To break or separate or to break apart, especially with force. 

  • To part, separate. 

noun
  • a separation into parts; a division or severance 

How often have the words split up and sunder occurred in a corpus of books? (source: Google Ngram Viewer )