Hi Chris. You’re real all right. Unless of course the person I met at the AGU a couple of years ago was an imposter. Anyway no one in their right mind would sue a geologist. All they would get for their efforts would be rocks.

When the Imperial Valley earthquake of 15 October 1979 (M=6.4) struck southernmost California, lots of scientists showed up from the U.S. Geological Survey. The flat, open farmland displayed many kinds of ground disturbance to advantage. But Robert Nason, a veteran USGS researcher, went indoors to chain grocery stores, examining the mess that the quake left behind and treating it like a strong-motion seismogram. Weak earthquake shaking tosses a few cans into the aisles, while stronger shaking throws everything off the shelves, then knocks down the shelves themselves.

Something I have always noted about quakes in our area is that shelves that are aligned north and south usually come through the quake pretty well. Not much stuff is knocked off the shelves. This isn’t the case with shelves aligned east and west. Just about everything comes off, even during a moderate quake. Another thing I have noted in regards to mobile home is that those that are set up so they run north and south will come down. Those that are set up so they run east and west will move on the blocks but almost never come down.

During the 1989 Loma Prieta quake, which centered 27 miles north of where I live my home moved about a half inch on the blocks. My home runs east and west and the blocks it sits on are aligned north/south. Most of the mobile homes on the west running streets came down, as they were aligned north and south. Most of the north/south aligned homes that didn’t come down had their support blocks aligned so that one set was north/south and the next set east/west.

My Mother and Aunt lived in mobile homes in Morgan Hill which is located about 5 miles east of the Loma Prieta quake. The most damage they received was to the skirts around the base of the homes. They looked as if someone rolled a log under them from front to back. Their homes were aligned north/south. I don’t recall if any of the homes in the park came down. It didn’t take me very long to figure out the earth movement in that area was different then the movement in the Hollister area.

By the way I’m still waiting for what you have to say about using boreholes to determine when and how many quakes have occurred at a given location. Take Care…Don in creepy town

http://geology.about.com/library/weekly/aa070598.htm

• Jim Brune Precarious Rocks