This boundary is the site of recurring earthquake activity and faulting
The boundary in question is most likely a plate boundary, specifically a tectonic plate boundary. Tectonic plates are large, rigid pieces of Earth's lithosphere that float on the underlying semi-fluid asthenosphere. They interact at plate boundaries, which can take various forms including divergent boundaries, convergent boundaries, and transform boundaries.
If the boundary is characterized by recurring earthquake activity and faulting, it is likely a transform boundary. Transform boundaries occur where two plates slide horizontally past each other. As the plates move, they can become locked due to friction, causing stress to build up along the boundary. When the stress is released suddenly, it leads to the occurrence of earthquakes. The faults associated with transform boundaries are commonly strike-slip faults, where the relative motion of the plates occurs mainly in a horizontal direction.
One well-known example of a transform boundary with recurring earthquake activity and faulting is the San Andreas Fault in California, USA. This fault marks the boundary between the Pacific Plate and the North American Plate, and it has produced numerous earthquakes over the years, including the disastrous San Francisco earthquake in 1906.