The very large range of spatial and temporal scales that these problems involve clearly demonstrate that GEM is an HPC-class problem. Current evidence indicates that forecasting the damaging earthquakes of magnitude 6 and greater almost certainly depends upon understanding the space-time patterns displayed by smaller events, e.g., the magnitude 3's, 4's and 5's. At least 40,000 km2 of fault area in southern California are capable of participating in magnitude 6 and greater events. Hence, needing a spatial resolution of about 100 m to eliminate grid-scale effects and to capture the physical processes of the magnitude 3 events, and a temporal resolution of 100 sec, one arrives at the conclusion that as much as 106 grid sites will be necessary for a maximally realistic simulation. If grid sizes at the 10 m scale are used to capture the failure physics of the magnitude 3 events, then 108 grid sites will be needed. Using current computational technology, run-time estimates of several months for this problem can be documented.