A strike slip fault is a fault in which the dominant displacement occurs horizontally and approximately parallel to the strike of the fault. The strike is the compass direction of a horizontal line along the fault plane, so strike slip movement means that the two blocks move laterally past one another rather than primarily moving vertically. Strike slip faults commonly form in regions dominated by shear stress, where rocks are subjected to forces that cause lateral deformation.
They can occur within tectonic plates and are especially important at transform plate boundaries, where adjacent plates move laterally relative to one another. Strike slip faults can be nearly vertical, although their geometry varies. They can generate earthquakes ranging from small events to extremely large ruptures when long sections of a major fault slip suddenly.
Strike slip faults are commonly classified as right lateral or left lateral, also called dextral or sinistral in geological terminology. Imagine standing on one side of the fault and looking across it toward the opposite side. If the opposite block appears to move to the right, the movement is right lateral. If it appears to move to the left, it is left lateral.
The classification concerns relative horizontal motion and does not simply refer to the compass direction in which a block travels. The sense of slip can be determined from displaced geological markers, roads, rivers, fences, rock formations, or earthquake focal mechanisms. A fault can also change its slip behaviour along its length or through time, particularly where it interacts with bends and branching structures.
The San Andreas Fault in California is a widely known example of a major right lateral strike slip fault. It forms part of the boundary between the Pacific Plate and the North American Plate and accommodates substantial horizontal relative motion. The North Anatolian Fault in Türkiye is another major strike slip system, while the Alpine Fault in New Zealand has both strike slip and reverse components and is therefore an example of oblique slip rather than a purely strike slip structure. Transform faults in ocean basins can also accommodate lateral plate motion, commonly offsetting segments of mid ocean ridges. These examples show that strike slip faulting occurs in diverse geological environments and is not restricted to continental landscapes.
Strike slip faults can have distinctive surface expressions. Lateral displacement may offset streams, ridges, roads, fences, rock layers, and other linear features. Bends in the fault can produce areas of local compression or extension even though the overall fault movement is predominantly horizontal. A releasing bend can create a pull apart basin where the crust locally extends, while a restraining bend can produce uplift and folding where the crust is locally compressed. These secondary structures mean that a strike slip fault system can contain normal and reverse faulting in addition to its main lateral motion. The resulting landscapes may therefore include basins, ridges, pressure ridges, sag ponds, and displaced drainage systems.
Earthquakes on strike slip faults occur when accumulated shear stress causes sudden lateral rupture. The rupture can propagate along the fault at high speed, producing strong ground motion over a wide region. Because the dominant displacement is horizontal, surface rupture may appear as roads, fences, streams, or other features shifted sideways. However, vertical motion can also occur where the fault geometry changes or where an oblique component is present.
Earthquake damage is controlled not only by the amount of lateral slip but also by rupture length, depth, magnitude, rupture directivity, local ground conditions, building vulnerability, and population exposure. A major strike slip earthquake can therefore be extremely destructive even when the fault produces relatively little permanent vertical displacement.
Strike slip fault systems often consist of multiple strands rather than a single continuous fracture. Step overs, bends, branches, splays, and connecting faults can distribute deformation across a broad zone. Some portions may be locked while others creep slowly, causing differences in earthquake behaviour along the same general fault system. Fault segmentation can influence whether an earthquake remains relatively small or ruptures across multiple connected segments. Scientists investigate these structures using field mapping, seismicity patterns, satellite geodesy, paleoseismology, trenching, lidar, and geological dating. Such studies help determine long term slip rates, past earthquake behaviour, and the spatial distribution of strain.
Strike slip faults are closely associated with transform boundaries, but not every strike slip fault is a plate boundary. Some occur within continents as part of broad zones of crustal deformation. They can connect other types of plate boundary or accommodate differences in motion between neighbouring crustal blocks. In oceanic settings, transform faults commonly offset spreading centres, and their active earthquake zones are concentrated in particular sections between ridge segments.
Beyond the active transform section, the former offset may remain as a fracture zone that records the history of seafloor spreading but is not necessarily an active plate boundary along its entire length. This distinction illustrates how fault activity and geological structure can change along the same feature.
Strike slip faulting should be distinguished from normal and reverse faulting according to the dominant direction of movement. Normal and reverse faults are primarily dip slip, meaning movement occurs up or down the inclined fault plane. Strike slip faults are primarily lateral, meaning movement occurs parallel to the strike. Oblique slip faults combine lateral and vertical components and are common where the regional stress field is not perfectly aligned with a fault. Fault classification therefore describes the geometry of relative displacement rather than assigning a permanent label to every movement event. A fault may exhibit different components of slip during different earthquakes, and its classification may depend on which component dominates over the relevant geological interval.
