I'm trying to understand why in the Loma Prieta quake the fault didn't crack through the earth, yet the earth cracked. It is very confusing. I've read several sites, have watched one video, and consistently it's stated that one of the surprises of this quake was that the fault didn't crack through the earth. Yet there are many pictures of the earth with many cracks in it, but they don't count. I guess they don't count because the cracks went from the crust downward due to various effects of the quake.

Anyway, I'm going to paste an especially confusing paragraph from some of my reading to see whether anyone here can crack it open in elementary terms:

"A somewhat surprising aspect of the October 17, 1989 Loma Prieta earthquake was the lack of recognizable surface faulting or rupture along the trace of the San Andreas Fault. Aftershock patterns (see the first page) demonstrated that actual fault rupture teminated approximately 5 km below the ground surface. Although no throughgoing fault rupture occurred at the surface, a 5 km wide zone of complex ground cracking formed along the summit and seaward flank of the Santa Cruz Mountains in the Summit/Skyland Ridge area between Highway 17 and the forest of Nisene Marks. These ground cracks varied widely in dimension and lateral extent, often occurring in complex interconnected patterns both along the upper slopes of ridges as well as along ridgetops themselves. "


OK. If I understand this, the fault cracked well below the earth's surface. And the ground cracking was simply consequential cracking, but not the fault.

Here's the url from the quote:

http://www.es.ucsc.edu/~es10/fieldtripEarthQ/Damage3.html


Thanks for any elucidating comments.
WW