"Preparation and good timing enabled Gareth Funning and a team of researchers to collect a unique data set following the 2014 South Napa earthquake that showed different parts of the fault, sometimes only a few kilometers apart, moved at different speeds and at different times.
Aided by GPS measurements made just weeks before the earthquake and data from a new radar satellite, the team found post-earthquake fault movement, known as afterslip, was concentrated in areas of loosely packed sediment. Areas where the fault passed through bedrock tended to slip more during the actual earthquake."