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Preliminary analyses of the 12/26/2004 Mw 9.0 Earthquake in Indonesia

The main shock on December 26, 2004 is the large green dot and seven days of aftershocks are smaller green dots. More recent earthquakes are shown on top of earlier events. Two permanent GPS stations, SAMP and NTUS, are also shown.

Coseismic offsets on the east coast of Sumatra

Dr. Jeff Freymueller (University of Alaska) has analyzed the most recent data from the CGPS site SAMP (Sampali, Medan, Sumatra), located on the east coast of Sumatra. The solutions for the coseismic offset below represent the average of one week before and one week after the quake. Pre-quake solutions use JPL final orbits, post-quake use JPL rapid, and all solutions have been independently transformed to ITRF2000.

Displacement (east-north-up):  132 mm, 17 mm, -17 mm
Formal uncertainty is about 3 mm, but not necessarily scaled sensibly.

Click on image to view the full-scale PDF file

Freymueller writes, "The plot is a baseline time series and represents fairly rapid solutions that can be improved. I suspect that there is a real post-seismic signal in the east component. There may be displacements at some of the IGS sites, but if so they are small and will require more care to resolve. Nevertheless, it is at least one displacement that can be added to a seismic slip model."

Dr. Cecep Subarya at BAKOSURTANAL, the Indonesian National Coordinating Agency for Surveys and Mapping, provides solutions for coseismic displacement at NTUS in Singapore.

Rupture Model

Dr. Chen Ji, Associate Scientist at the California Institute of Technology Seismological Laboratory, has calculated a preliminary rupture model of a limited portion of the fault zone for the Mw 9.0 earthquake off the western coast of Northern Sumatra.


UNAVCO Community Data and Global Strain Rate Map (GSRM) Models in the Indonesian Region

The maps below show the locations of stations from Indonesian campaigns with data archived at UNAVCO (red dots). All campaigns are from Scripps Institution of Oceanography, Dr. Yehuda Bock, Principal Investigator. Shown as green dots are the recent earthquakes of December 26 (large dot) and subsequent smaller earthquakes in the following 7 days.

Map showing location of GPS campaign survey sites
(red dots)

UNAVCO Data Archive Group ID

Link to archived metadata

Date of GPS Campaign



Indonesia (APEX) 1989

1989 Sep 20



Indonesia (APEX) 1990

1990 Aug 10

MapMap 1Map 2


Indonesia (APEX) 1993

1993 Oct 03



Indonesia 1991

1991 Jul 19

The maps below show GSRM velocities (http://gsrm.unavco.org/) (Kreemer, et al. 2003). Modeled plate boundaries by Peter Bird are shown in light blue lines and modeled plate boundaries by the U. Texas Plates Project are shown in yellow (transform), orange (spreading), and dark blue (subduction) (http://www.ig.utexas.edu/research/projects/plates/plates.htm).


Last modified: 2020-01-28  22:54:13  America/Denver