Possibly a habitational name for someone from Zambrana, a town in the province of Álava in Spain.
Originally denoted a person from Zamora, the name of both a province in Spain and its capital city.
Means "old bridge", from Basque zubia
"bridge" and zahar
"old". A famous bearer is the Spanish soccer player Andoni Zubizarreta (1961-).
From the name of a Spanish town, formerly named Estuniga in Basque, possibly derived from Basque istuin