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section south of Hollister to Parkfield. The northern half of the San Andreas Fault is further segmented near San Francisco. The largest historical earthquake on the Peninsula segment was the 1906, San Francisco Earthquake with a moment magnitude of 7.8 (Well and Coppersmith, 1994). This earthquake was due to simultaneous rupture of the North Coast and Peninsula segments. The 2003 U. S. Geological Survey Working Group on earthquake probabilities in California estimated the expected magnitude on the San Andreas fault for a repeat of the 1906 earthquake as M=7.9 with a return period of approximately 300 years. Since the last large event was in 1906, the probability that the magnitude 7.9 event will occur in the next 30 years was estimated at less than 10% with good confidence. Using the Working group procedure, I computed the probability that the North Coast segment will experience a magnitude 7.9 earthquake during the next 100 years to be about 20%. This probability is lower than the chance of 1/3 in 100 years discussed above. Although it is more conservative, there is precedence for using a magnitude 8 event on the San 0 Andreas. 1 recommend using an MPE of magnitude 8.0 at a distance of 126 km for the San Andreas Fault. Ground Motions Horizontal ground motions (i.e., PGA and spectral acceleration) are estimated for each seismic source based on the parameters listed above (also see table 2). Ground motions are estimated based on the recently developed PEER NGA empirical attenuation models: Abrahamson and Silva (2006), Boore and Atkinson (2006), Campbell and Bozorgnia (2006), and Chiou and Youngs (2006). The average PGA values for each source are listed in Table 2 and the average horizontal spectra (5% spectral damping) are plotted in Figure 2a. These ground motion values are for an average shear wave velocity of 760 m/sec in the top 30 meters of the site. A depth to the 2.5km/sec boundary of 0.393km was used for the Campbell and Bozorgnia (2006) NGA model. The CRCV source controls the MPE ground motions for PGA and periods less than approximately 0.4 seconds. For spectral periods greater than 0.4 sec, the larger and C