The occurence of "far-field aftershocks" monotonically decreases with distance from the fault rupture, so far as we know. The standard explanation is that the shaking sets off the FF aftershocks with the normal aftershock delay seen for nearby aftershocks. The shaking beyond 1000 km distance is small, and beyond 10,000 km is very weak indeed.

Yesterday I got up early in DC, and was tired when I wrote the post in late evening in LA.

John