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I just got another reply to my "seismic safety of an underground structure" e-mail. Here it is:

In response to your e-mail to ATC, 8/8/97:

Underground structures would fare better than surface structures, other things being equal, because the ground shaking is less there; it increases as it ascends from bedrock to the surface. The seismic structural engineering design community can design for you a structure that will fare well against any ground shaking; it might cost, though. The Richter scale loses much of its meaning higher than 7 or 8; you must talk "moment magnitudes" after that. The maximum shaking doesn't get much bigger as the magnitude rises above 7 or so; it lasts longer instead. Reinforced is fine, but domes or geodesic domes are nothing special in the horizontal shaking of an earthquake; they are just lightweight roofs that hold themselves up against their own weight, which is acting vertically. The comment on underground structures applies to domes, too. Your question regarding magnitudes of 15 indicate naivete.

A. Gerald Brady, P.E., Ph.D.
ATC, 555 Twin Dolphin Dr., Suite 550
Redwood City, CA 94065, USA
415-595-1542, fax:415-593-2320

Offered by Peter.