Chuck, I've been on the road and just arrived home, so I'm only now getting to today's emails. Just so you know I wasn't ignoring you... Much of the ancient lake bed from Lake Bonneville is prone to "soil liquefaction," which I think is the first risk to which you refer. If wet enough, loose soils, primarily sandy soils may lose strength and essentially become a viscous liquid during ground shaking. Here's a link to a short discussion and a liquefaction potential map for most of the Salt Lake area: http://geology.utah.gov/online/pdf/pi-25.pdf. During an earthquake, the most likely mechanism for the failure of soils on mountainous slopes is not necessarily the same as soil liquefaction, although saturated soils are still more likely to fail. Most of the risk of homes sliding off the mountains that your professor described is not due to anything special about the Salt Lake area. Obviously, the very nature of mountains (sloping surfaces, unconsolidated slopes, etc.) increases the potential for soil failures, especially when the earth shakes. That view comes with a very high risk, as folks in southern California and other areas keep experiencing, with or without an earthquake. One other possibility (Rodger may know more about this) is that numerous developments in the foothills of the Wasatch Mountains have been or are being built right on top of some of the minor faults that are part of the Wasatch Fault system. Fault escarpments as high as 30 feet and only a few hundred years old have now become landscape features in "exclusive" neighborhoods. (I'll have to do some digging to find photos.) I don't think that there are many planning/zoning controls in place in Utah to prevent people from being so foolish. So, for what it's worth, there's my professional lesson for the day. (Invoice to follow.) Kim -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, March 22, 2011 2:26 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Japan Earthquake Discussion Kim, it's been a long time since I was in the pre-architecture program at the U, but I seem to recall that in addition to failed structures themselves, much of the damage here would be the result of all the construction built on ancient sand and gravel bars surrounding the valleys. I recall one professor who claimed that most of the bench structures will simply slide-off the side of the mountain when the "big one" hits and all that clay, sand, and buried talus turns to jello. All those million-dollar houses will become buried in a pile of rubble at the bottom of the benches. Can you comment on that, as a professional architect?