Well, there was a different motion. This event was a reverse-faulting earthquake almost directly below Christchurch, whereas Darfield was a strike-slip event some distance away. It would not be very surprising if residents perceived this event to have a much stronger vertical component to the shaking. That does not necessarily influence the pattern of damage, but what is salient is that this earthquake generated very high ground accelerations for a 6.3 event - max PGA was 1.27 g.
The strong ground motion community are going to be picking over the data from this earthquake for quite some time, I expect.
Roger Musson
British Geological Survey
West Mains Road
Edinburgh EH9 3LA
tel: +44 (0)131-650-0205
fax: +44 (0)131-667-1877
> -----Original Message-----
> From: Natural hazards and disasters [mailto:NATURAL-HAZARDS-
> [log in to unmask]] On Behalf Of Garry de la Pomerai
> Sent: 22 February 2011 15:26
> To: [log in to unmask]
> Subject: Re: Trees, Airplanes, and Earthquakes
>
>
> et all,
> it seems that accounting for the accumulative affect of previous
> events, such as last years quake with relatively little damage from a
> 7.2/3, will answer some questions of why previously resilient buildings
> have now collapsed.
> my question is , how much was assessed since last years quake, ie the
> cathedral tower, and how detailed if they were assessed? Maybe what
> is needed post a larger quake with relatively little damage, is a very
> much more thorough 'internal' assessment of engineered structures, and
> wider assessment of the older non-engineered.
> I did hear one person say that she believed that there was a different
> motion to this quake in comparison to last years..... might help
> provide some answers.
>
> <javascript:void(0)>
> Garry
> de la Pomerai
>
>
>
> -----Original Message-----
> From: Justin Sharpe <[log in to unmask]>
> To: [log in to unmask]
> Sent: Tue, 22 Feb 2011 13:29
> Subject: Re: Trees, Airplanes, and Earthquakes
>
>
> Ilan,
> I also noticed that the triage centres that I have seen on the news
> seem to be
> in public parks, which makes sense in some ways, but there were many
> people
> underneath trees, which is not. The city of Christchurch has been
> affected by
> liquefaction in many places which amplifies shaking but may also have
> affected
> the ground underneath the trees. They may not have fallen thus far, but
> I think
> evacuating to these areas is fraught with risk.
>
> Justin
>
> Sent from my iPad
>
> On 22 Feb 2011, at 09:40, Ilan Kelman <[log in to unmask]> wrote:
>
> > Looking at the first images from Christchurch, I am curious if anyone
> has
> comments regarding why few trees appear to have fallen down, even when
> they are
> near severely damaged buildings or big cracks across roads? Perhaps
> other images
> show fallen trees?
> >
> > Also, in 2006, I contacted three airline companies enquiring if they
> could
> provide information regarding their procedures for earthquakes
> occurring during
> takeoff or landing. None was interested in discussing the topic. Now,
> it has
> happened http://www.stuff.co.nz/4689348/Plane-lands-as-quake-strikes-
> runway
> fortunately without a major incident involving the aircraft. Any
> comments on
> such a situation?
> >
> > Our thoughts are with those affected,
> >
> > Ilan
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