In 1868, there was a large earthquake due to movement along the Hayward fault from Hayward to Fremont.  Pressure and stress have been building along the Hayward fault since 1868 and it could be released causing another earthquake anytime.  Some of the stress is being released through fault creep (here it is about 9 mm/yr) and offset can be seen in the human structures located here (curbs, streets, buildings, and parking lots located within about a 3 square block area).