Cathyrn,
It may have been felt more strongly in Los Angeles than in San Francisco for 2 reasons:
1: The fault may have ruptured from NW to SE-the mainshock is plotted to the NW of most of the aftershocks. there is a directivity effect that sends more energy in the direction of fault propagation.

2: Los Angeles basin is like a bowl of jello. Long-period waves from distant quakes are amplified in the basin.

But, your comment that the San Andreas focuses its energy to the north is incorrect. The damage in 1989 was more to the north because:
1: That is where the cities are
2: There are bad ground conditions (fill) in those cities.

The 1989 quake ruptured in both directions, I think. The next San Andreas quake may well direct its energy the other way, or equally both ways.
Chris