C

Maybe the shaking lasted a minute, but I doubt the ground rupture lasted more than 15 seconds.
The cracks usually spread around 2 km/s, and the rupture was about 20 km long.

The focusing of the radiated waves usually is done by permanent geological features, like deep sedimentary basin boundaries, so we don't think any of these earthquakes has much to do with how the motions in the subsequent events reverberates.

Aftershocks of Sylmar probably continue to this day, but so infrequently that we can't tell them from the background seismicity any more.

I'm up in the Santa Monica mts, although it would be easier to get my morning coffee if I lived down in the village.

J