Sliphastighet

Sliphastighet, or slip velocity, is a geophysical term that describes the instantaneous rate at which two sides of a fault move relative to each other along the fault plane. It is the time derivative of slip, often denoted v = ds/dt, and is measured in units such as meters per second.

In tectonics, sliphastighet can refer to both seismic slip that occurs during earthquakes and aseismic slip that takes place more slowly, such as fault creep or slow-slip events. Long-term plate motion between rigid blocks operates on much slower timescales, typically measured in millimeters per year, whereas seismic slip can reach much higher speeds for brief periods.

Measurement and interpretation rely on a combination of seismic data, geodetic sensors (GPS and InSAR), borehole strainmeters, and slip inversions. By analyzing time-dependent displacement along a fault, scientists estimate the slip history and derive the slip velocity during different phases of faulting.

Sliphastighet varies widely. During earthquakes, slip velocities commonly reach values up to a few meters per second in the slipping patches, with shorter-lived peaks. In contrast, aseismic slip and slow-slip events occur at much smaller velocities, spanning mm to cm per year over longer durations. The velocity profile of slip influences the radiated seismic energy, rupture propagation, and ground shaking.

In modeling, slip velocity is a key parameter in frictional and rupture simulations, helping to constrain how faults slide under stress. It is distinct from rupture velocity, which describes how quickly the rupture front itself propagates along the fault.