ion. Although they may suffer some damage, they are unlikely to collapse because the strength of the strongly jointed timber-frame can easily support the light loads of the roof and the upper stories even in the event of strong vertical and horizontal ground motions.Seismologists have observed that some districts tend to repeatedly experience stronger seismic shaking than others do. This is because the ground under these districts is relatively soft. Soft soils amplify ground shaking. If you live in an area that in past earthquakes suffered shaking stronger than that felt in other areas at comparable distance from the source, you are likely to experience relatively strong shaking in future earthquakes as well. An example of this effect was observed in San Francisco, where many of the same neighborhoods were heavily damaged in both the 1906 and 1989 earthquakes. The influence of the underlying soil on the local amplification of earthquake shaking is called the site effect. Other factors influence the strength of earthquake shaking at a site as well, including the earthquake's magnitude and the site's proximity to the fault. These factors vary from earthquake to earthquake. In contrast, soft soil always amplifies shear waves. If an earthquake is strong enough and close enough to cause damage, the damage will usually be more severe on soft soils. There have been many major earthquakes in the bay area. In all of the major earthquakes there has been deaths in direct result of building design and earthquake safety laws. In 1868 October, 21 there was one of the most destructive earthquakes San Francisco has had. It ruptured from the southern end of the Hayward fault. It had a magnitude of 7.0. Know as the "Great San Francisco Earthquake" killing over twenty people and injuring over sixty people and having a destruction cost of $300,000 which was a lot of money back then. In 1906 April 18 the San Andreas fault ruptured with a magnitude of 7.7....
