ith no vertical displacements. Rayleigh and Love waves always travel slower than P waves and usually travel slower than S waves.Earthquake design in the Bay Area has become a pressing issue. We have seen the importance of earthquake safety in the bay area. The San Francisco Bay Area is part of a very complex plate boundary system between the pacific and the northern American plates. Near Hollister, the Calaveras fault branches off from the San Andreas Fault towards the north. The Hayward fault branches off from the Calaveras towards the northwest. At a much smaller scale many thrust faults run parallel and cross the San Andreas Fault. Although most of the present day seismic activity in the Bay Area comes from the major faults (San Andreas, Hayward-Mission creek, Concord-Calaveras, and the Antioch faults) ten percent happens in the minor and unmapped faults. Geologists and engineers use risk assessment maps, such as geologic hazard and seismic hazard zoning maps, to understand where faults are located and how to build near them safely. Engineers use geologic hazard maps to predict the average ground motions in a particular area and apply these predicted motions during engineering design phases of major construction projects. Engineers also use risk assessment maps to avoid building on major faults or to make sure that proper earthquake bracing is added to buildings constructed in zones that are prone to strong tremors. They can also use risk assessment maps to aid in the retrofit, or reinforcement, of older structures.In urban areas of the Bay Area, the seismic risk is greater in non-reinforced buildings made of brick, stone, or concrete blocks because they cannot resist the horizontal forces produced by large seismic waves. Fortunately, single-family timber-frame homes built under modern construction codes resist strong earthquake shaking very well. Such houses have laterally braced frames bolted to their foundations to prevent separat...
