Testing transform faults
A student of Jack Oliver, Sykes obtained earthquake-mechanism solutions near the Mid-Atlantic Ridge in 1966. The motions agreed with John Tuzo Wilson’s transform-fault interpretation and supported seafloor spreading at ridge crests.
References: [1]
Earthquakes and subducting plates
In 1968 he collaborated with Oliver and Bryan Isacks to connect earthquake observations with plate tectonics, investigating motion where one slab descends beneath another and linking ocean-boundary evidence with deeper earthquakes.
Hazard assessment and nuclear tests
He later investigated long-term patterns of great earthquakes, seismic risks to nuclear facilities and detection of nuclear-bomb tests. These applications connect geophysical observation with public safety; long-term hazard assessment does not determine the exact time of the next earthquake.
References: [1]