[IGSMAIL-6089]: Predicted displacements for Chile Earthquake

[Jeff Freymueller]

******************************************************************************
IGS Electronic Mail      01 Mar 12:30:14 PST 2010      Message Number 6089
******************************************************************************

Author: Jeff Freymueller

I used the USGS finite fault slip model for the Chile earthquake, and  
the Coulomb program also available from the USGS, to compute predicted  
displacements for IGS and other sites across southern South America.  
Gavin Hayes of USGS (National Earthquake Information Center) computed  
the fault model. The USGS NEIC is putting a lot of information out  
about large earthquakes on a very rapid basis now, and there will be a  
page for every significant (large-enough) earthquake with slip models  
and so on. Its a great resource.

The finite fault model is at:
http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010tfan/finite_fault.php
At the bottom of the page you will find links to the slip distribution  
in various formats.

The Coulomb program is available at:
http://quake.usgs.gov/research/deformation/modeling/coulomb/index.html

Coulomb will also make spectacular plots, although I had trouble  
trying to make it do a plot for a large area -- not sure whether it  
was my mistake or a bug that caused that problem.

The displacements computed at this point should be used as a guide in  
assessing the likelihood that any station has shifted, not for  
corrections of the data. The inversion available so far is based only  
on teleseismic data (from global stations), and such inversions have  
some tradeoffs that can result in the entire slip distribution being  
shifted somewhat, and also from some potential space vs. time  
tradeoffs. The total seismic moment is probably well constrained. Some  
details of the distribution of slip are more likely to change as more  
data are added, especially geodetic data.

The forward calculation here also uses a half-space to represent the  
earth. On the scale of South America, a flat earth approximation is  
probably not good enough. However, it is probably not too bad as the  
effects of sphericity of the earth and of elastic layering of the  
earth can sometimes be of opposite sign, making this a reasonable  
first approximation.

So in the near field the details of the slip model are probably what  
limit the accuracy of predictions, and in the far field it is most  
likely the half-space approximation in the forward calculation that  
limits the accuracy. The details of the slip model won't matter for  
the far-field displacements.

Note that some sites on the Atlantic coast of Argentina are predicted  
to have significant displacements, at the 10-20 mm level. Other sites  
may well have significant displacements that are too small to see by  
eye (few to several mm).

Predicted displacements in meters:

longitude	latitude	CalcEast	CalcNorth	CalcUp	
(deg)	(deg)	(m)	(m)	(m)	
-73.025	-36.844	-1.886852	-0.227121	-0.014187	CONZ
-73.025	-36.843	-1.888739	-0.22774	-0.013635	CONT
-71.626	-33.027	-0.415198	0.079196	0.340309	VALP
-71.532	-37.339	-0.520062	0.193156	-0.127075	ANTC
-70.669	-33.15	-0.45218	-0.151496	-0.254345	SANT
-68.233	-31.602	-0.072937	-0.029996	-0.00772	CFAG
-70.338	-27.385	-0.002328	-0.000162	-0.007618	COPO
-64.47	-31.528	-0.036732	-0.009409	0.001671	CORD
-65.408	-24.727	-0.00395	-0.00157	-0.002441	UNSA
-70.132	-20.274	-0.000136	0.000282	-0.002255	IQQE
-71.493	-16.466	0.000153	0.000203	-0.001464	AREQ
-47.878	-15.947	-0.001504	-0.000513	-0.000122	BRAZ
-47.925	-25.02	-0.00381	-0.000882	0.000376	NEIA
-49.231	-25.448	-0.004212	-0.000988	0.000404	UFPR
-44.985	-22.687	-0.002757	-0.000685	0.000239	CHPI
-71.892	-45.514	-0.002002	-0.00028	-0.004948	COYQ
-57.531	-38.036	-0.017226	0.002936	0.002685	MPLA
-62.269	-38.701	-0.031203	0.008351	0.004018	VBCA
-65.107	-43.299	-0.013812	0.008086	-0.00027	RWSN
-57.932	-34.907	-0.019244	0.000357	0.002862	LPGS
-58.519	-34.574	-0.020702	0.000017	0.002995	BUE1



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:   907-378-7556
Fairbanks, AK 99775-7320           email: jeff.freymueller at gi.alaska.edu
URL: http://www.gps.alaska.edu/jeff/jeff.html

Download Alaska GPS data: ftp://gps.alaska.edu/pub/gpsdata/