"Well - excited and scared"

[steuard]

I just had my first real earthquake! Sure, on a couple of occasions I've felt a quick jolt around the house, but never enough to even be completely sure it was actually a quake. No doubts about this one, though. While my first thought was "What did they drop upstairs this time?", I quickly realized that the rumbling and shaking was stronger and longer lasting than the usual bumps from the lab above, and I scrambled under my desk just as the ripples hit. (Thanks to my Fields and Waves class at Harvey Mudd, I know pretty precisely what was going on at each stage of the way.)

It didn't last long, and it didn't seem like anything disastrous had happened, but we were evacuated from the college buildings as a precaution. I'm obviously new at this (and I may have been more flustered than I thought), because I didn't think to grab my bag lunch off of my desk (it was almost noon) and or even to close my door behind me (we've got laptops in here). Fortunately, someone else closed it for me, and they let us back in before I got too hungry. All in all, it made for a more interesting day, and happily it sounds like there weren't any serious injuries anywhere (one news story commented that a couple of people had minor head injuries from taking cover under tables). If you want all the latest California earthquake news, I highly recommend this USGS site.

Comments

[steuard.livejournal.com]

By "quake-survival features", I was referring (perhaps entirely incorrectly) to the notion I'd picked up somewhere that many buildings in California these days are somehow partially decoupled from motions of the ground (due to clever design of the foundation-ground interface allowing some relative motion, perhaps?). So I wondered whether the broader rolling feeling I got toward the end of the shaking might have been the building settling into some resonant frequency of such a system after a lag. I'll readily admit that the premise could be way off, though, and I still think the surface wave theory is more likely.

[akjdg.livejournal.com]

I'm not really up to speed on 'active' seismic design, but the two general approaches I'm aware of are:

(1) actively controlled mass that is actuated against the sensed building motion to largely negate the building sway and keep it somewhat still. Typically employed in high rises.

(2) Ball bearing isolation structure between the foundation and building. Building is on rollers so as the ground moves laterally beneath, the building stays relatively still. The ball bearings are in little gravity wells so the building generally stays where it belongs. This might be employed to retrofit an old building (say a masonry building) that is valuable but not readily retrofitted by other means.

In terms of passive design, it is basically a matter of making sure the building's rigidity and flexibility are designed to survive an earthquake and yet be comfortably stiff under normal design loads.

I think your experience is more likely the surface waves.