Delivered-To: igsmail@igscb.jpl.nasa.gov Date: Thu, 9 Oct 2003 10:33:52 -0800 Subject: [IGSMAIL-4643]: Re: [IGSMAIL-4642]: IGS00 (v2) Cc: "'igsmail@igscb.jpl.nasa.gov'" To: =?ISO-8859-1?Q? "Ferland,_R=E9mi" ?= From: Jeff Freymueller In-Reply-To: <5ACEEE96F4F9D41190790002A528B51E78E7A3@s0-ott-x11.nrn.nrcan.gc.ca> Message-Id: <21ED8AA2-FA87-11D7-A2B1-0003931DE4DC@giseis.alaska.edu> Sender: owner-igsmail Precedence: bulk ****************************************************************************** IGS Electronic Mail 09 Oct 11:33:54 PDT 2003 Message Number 4643 ****************************************************************************** Author: Jeff Freymueller Users of IGS2000(v2) should be cautious in constraining the position of=20= the IGS site FAIR, as it is still undergoing time-dependent deformation=20= following the November 2002 Denali Fault Earthquake. In addition to the large (~6 cm) displacement at the time of the=20 November 3, 2002 Denali Fault earthquake, the site has experienced a=20 further ~2 cm of postseismic deformation. The postseismic deformation is=20= a transient signal and even treating the site has having a new velocity=20= after the earthquake is an approximation because the postseismic=20 deformation decays with time. For example, about half of the total=20 postseismic deformation to date occurred in the first two weeks after=20 the earthquake. The accuracy of the post-earthquake velocity thus=20 depends on the exact time interval used to estimate it. In particular,=20= this means that if you extrapolate the immediate post-earthquake=20 velocity very far into the future you will run into problems as the=20 postseismic transient decays away. Fortunately, the total postseismic deformation is fairly small, and=20 based on Remi's description I suspect that any errors due to=20 postseismic deformation are presently at the 1-2 mm level, but I would=20= not suggest extrapolating the post-earthquake velocity more than several=20= months into the future in order to maintain this level of accuracy. We are working on models to describe and explain the time-dependent=20 deformation following the earthquake, but due to a heavy fieldwork load=20= it will be a few months before they are ready. Jeff On Thursday, October 9, 2003, at 09:57 AM, Ferland, R=E9mi wrote: > 4) Sites with different alignment & realization points > > Six sites used in the reference frame realization had > experienced significant discontinuity since the original > IGS realization and since ITRF2000 became official. In the > IGS cumulative solution (updated weekly), at stations with > identified discontinuities, the position/velocity were > estimated independently. For the alignment/realization, > the independent velocity estimates at a station were > combined to provide a unique velocity per site. The sites > with estimated discontinuity are: > > BILI COCO FAIR GUAM HOFN KOKB > > The cumulative solution for GPS week 1231 (IGS03P33.snx) > was used for the proposed IGS2000(v2). > Dr. Jeffrey T. Freymueller Office: 907-474-7286 Geophysical Institute Fax: 907-474-7290 University of Alaska, Fairbanks Home: 907-479-3550 PO Box 757320 Cell: 907-322-7632 Fairbanks, AK 99775-7320 email: jeff@giseis.alaska.edu or=20 jeff.freymueller@gi.alaska.edu URL: http://www.aeic.alaska.edu/Input/jeff/jeff.html Download Alaska GPS data: http://www.aeic.alaska.edu/Input/akda/