Delivered-To: igsmail@igscb.jpl.nasa.gov Subject: [IGSMAIL-5082]: IGS and the Earthquake offshore Sumatra From: "Gerd Gendt (forwarded by A. Moore)" To: igsmail@igscb.jpl.nasa.gov Content-Type: text/plain Message-Id: <1105154647.17524.33.camel@localhost.localdomain> Date: Fri, 07 Jan 2005 19:24:08 -0800 Content-Transfer-Encoding: 7bit Sender: owner-igsmail Precedence: bulk ****************************************************************************** IGS Electronic Mail 07 Jan 18:22:14 PST 2005 Message Number 5082 ****************************************************************************** Author: IGSACC Dear IGS Community, we all were shocked by the effect of the earthquake offshore the coast of Sumatra on December 26 and the tsunami events associated with it. The question naturally arises whether (a) the IGS products were negatively affected by the event and whether (b) the event left its traces in the IGS products. Let me first answer the questions: (a) Quality of the IGS products; IGS Network To the best of my knowledge as IGS analysis coordinator there was no negative impact of the earthquake on the quality of IGS products. It is in particular worth mentioning the that the "rapid orbit contributions" were of the same quality as usual. This also implies that the IGS rapid orbits for the time interval covering the terrible event are of comparable quality as for the days before and after the event. This is important to know for analysts using the IGS products for further analyses in the region affected. They can fully rely on the global terrestrial reference frame (ITRF2000/IGb00) as materialized by the IGS products. Of fundamental importance for the IGS is its global network. From all stations located around the northern Indian Ocean (BAKO, BAN2, COCO, DGAR, HYDE, IISC, MALI, NTUS, REUN, SEY1) only SEY1 stopped its tracking because of the tsunami. Therefore continuous regional data are available for detailed analyses. High-rate data are recorded at BAN2, IISC, REDU, JOGJ. (b) Visibility of the event in the IGS products. - In IGS mail no. 5069 sent out on December 29 (by Urs Hugentobler/CODE AC Team) possible effects on the earth rotation were mentioned. In essence the actual motion of the pole was compared with a predicted pole. Effects, mainly in the y-component of the pole of (at maximum) 2.7 mas were reported. - Today we can say that in essence the same motion of the pole was also observed by the other analysis centers (therefore also reflected in the IGS rapid product - see http://igscb.jpl.nasa.gov/images/Dec2004EQ.Gendt.gif ) and that it seems to be above the noise level. No clear signal was found in the determined length of day (lod). - The IGS will continue to analyze the data to improve our understanding of the geophysical processes. We do not comment on the origin of the motion. Further analysis will show what part of the polar motion can be attributed to the observed excursion of the pole. The IGS only provides observational evidence, no interpretation. - First evidence that the stations NTUS and IISC(BAN2) (1000 km from the epicenter) are shifted ~1-2 cm in the eastern direction can even be obtained using the Precise Point Positioning with the IGS Rapid orbits and clocks (see attached plot), and are clearly seen from the Final analysis. Station displacements will be best seen in the IGS Final products (where all station coordinates are left free). This analysis will become available about one week from now. Preliminary reports of the IGS analysis centers indicate that station motions of the order of 1-2 cm are likely to have occurred. Some of the centers even excluded stations from the list of fixed fiducial sites for their analyses. We are not aware of "dramatic" displacements (5 cm or more) in the stations defining our reference system. More information concerning station motion will be provided on the occasion of producing the IGS Final products. Let me point out that this is a preliminary summary. It is based on - reports by the IGS Analysis Centers, - the analysis performed in the context of the IGS combination, - personal communications Please check our IGS web sites: http://www.gfz-potsdam.de/igsacc http://igscb.jpl.nasa.gov/network/netindex.html Best regards Gerd Gendt, IGS Analysis Coordinator