Physics of the Earth and Planetary Interiors

80 J.C. Ruegg et al. / Physics of the Earth and Planetary Interiors 175 (2009) 78–85

ber 1996 we used nine Ashtech Z12 with geodetic L1/L2 P antenas

(ASHP12) and three Trimble SSE receivers with geodetic L1/L2 SSE

antenas.

Eight new sites were installed during the March 1999 measurement

campaign in the southern part of the 1996 network in order to

complete the southern profile between the Arauco peninsula and

the foothills of the Andes (LLI, RAQ, CAP, PUL, LAJ, SLT, SGE) (Fig. 1).

We used seven Ashtech Z12 equipped with choke-ring antennas.

At the same time, 13 points of the 1996 network were measured

again, providing a first estimation of the interseismic velocity field

(Ruegg et al., 2002). Most of the sites were equipped with brass

benchmarks sealed in bedrock outcrops, but the measurements

were done using tripods and optical tribrachs which enable centering

with only sub-centimeter accuracy. However, most of the

sites were equipped with three auxiliary points allowing a better

permanency.

Finally almost the entire networkwas resurveyed in March 2002

using Ashtech Z12 equipped with choke-ring antennas. During all

campaigns each site were measured for 12–24 h per day over 2–4

days, while three points (QLA, PUN, CO6) were measured continuously

in 24-h sessions during 1 week.

Table 1

Average short (<300 km) baseline repeatabilities (root mean square scatter about

the mean) for each of the three campaigns. Values are in mm.

December 1996 March 1999 April 2002

North rep. 3.8 2.4 2.5

East rep. 4.5 2.5 3.0

Vertical rep. 14.8 12.6 9.7

The current solution gives velocities at 36 sites determined over

the 6 years period.We analyse the GPS data in 24-h sessions to give

daily estimates of station position using the GAMIT software (King

and Bock, 2000), choosing the ionosphere-free combination, and

fixing the ambiguities to integer values.We use precise orbits from

the International GPS Service for Geodynamics (IGS) (Beutler et al.,

1993). We also use IGS Tables to describe the phase centers of the

antennae. We estimate one tropospheric vertical delay parameter

per station every 3 h. The horizontal components of the calculated

relative position vectors (Table 1) are accurate to within a few millimetres

for pairs of stations less than 300 km apart, as measured

by the root mean square (RMS) scatter about the mean (the so-

Table 2

Site positions and velocities, in ITRF2000 and relative to South America plate. Latitude and longitude are in decimal degrees. All velocities and velocity uncertainties are in

mm/year.

Site Position Velocity/IRTF2000 Velocity/SOAM Uncertainties

Longitude Latitude Vlon Vlat Vlon Vlat s lon s lat Corr.

BAT −71.962 −35.307 32.56 19.62 33.21 9.24 1.28 1.17 0.025

CAP −73.272 −37.245 34.47 27.41 34.74 17.15 2.83 1.79 0.093

CHL −72.205 −36.639 26.65 18.89 27.11 8.53 1.58 1.22 0.013

CLM −72.812 −36.236 33.08 23.02 33.53 12.72 1.54 1.21 0.003

CLP −71.625 −37.336 16.77 11.50 17.21 1.09 1.30 1.19 0.026

CO1 −72.415 −35.318 36.41 21.55 37.01 11.21 1.49 1.19 0.002

CO2 −72.491 −35.412 34.65 22.97 35.23 12.64 1.61 1.25 0.025

CO4 −72.626 −35.586 34.70 23.97 35.25 13.65 1.47 1.22 0.019

CO6 −72.606 −35.828 34.32 23.24 34.84 12.92 1.24 1.15 0.022

CO7 −72.639 −35.843 35.48 23.13 36.00 12.81 1.60 1.24 0.048

CO8 −72.744 −35.949 35.46 23.61 35.95 13.30 1.75 1.27 0.052

COLB −71.347 −35.677 27.21 15.83 27.88 5.39 1.23 1.16 0.019

CT2 −72.255 −35.464 34.76 20.56 35.36 10.20 1.62 1.22 0.014

CT3 −72.086 −35.558 33.04 20.26 33.65 9.89 1.42 1.21 0.013

CT4 −71.777 −35.616 30.08 17.46 30.71 7.06 1.40 1.25 0.004

CT6 −71.069 −35.709 22.49 17.56 23.19 7.09 1.27 1.17 0.015

CT7 −70.834 −35.815 17.86 13.48 18.57 2.99 1.41 1.18 −0.002

CT8 −70.399 −35.991 9.84 11.34 10.58 0.81 1.23 1.10 0.033

GUA −72.333 −37.346 22.92 16.56 23.28 6.21 2.60 1.97 0.232

LAJ −72.697 −37.255 25.86 20.55 26.19 10.24 1.62 1.45 0.024

LLA −71.344 −37.369 14.79 10.95 15.26 0.51 1.31 1.20 0.025

LLI −73.569 −37.192 42.29 24.92 42.54 14.69 2.28 1.65 0.090

LTA −73.142 −37.059 30.95 23.87 31.26 13.60 1.60 1.24 −0.003

MIR −71.75 −37.330 16.54 12.60 16.97 2.20 1.41 1.22 0.033

MRC −71.955 −37.411 18.62 14.02 19.01 3.64 1.30 1.19 0.026

NIN −72.437 −36.410 34.76 15.56 35.23 5.22 1.28 1.17 0.020

PTU −72.269 −35.172 32.02 22.88 32.66 12.53 1.37 1.18 0.032

PUL −72.942 −37.285 30.16 21.03 30.46 10.74 1.62 1.45 0.027

PUN −71.957 −35.750 31.30 19.90 31.90 9.52 1.24 1.16 0.021

QLA −72.125 −36.085 29.87 18.28 30.41 7.91 1.23 1.15 0.021

RAQ −73.436 −37.256 36.44 24.51 36.69 14.27 2.43 1.65 0.087

SGE −72.231 −37.393 23.90 16.81 24.27 6.45 2.14 1.60 0.088

SLT −72.384 −37.216 27.66 18.28 28.03 7.94 1.63 1.47 0.021

UCO −73.035 −36.829 33.77 23.05 34.12 12.77 2.16 1.67 0.045

DGF −70.664 −33.457 22.93 18.36 23.94 7.86 2.27 1.58 0.018

Permanent sites

SANT −70.669 −33.150 19.39 16.64 20.44 6.14 0.79 0.76 0.013

AREQ −71.493 −16.466 14.20 14.89 17.12 4.46 4.50 2.80 0.075

BRAZ −47.878 −15.947 −4.32 12.31 −0.08 0.64 1.00 1.00 0.000

EISL −109.383 −27.148 66.00 −7.72 65.27 −12.70 0.92 0.89 −0.007

GALA −90.304 −0.743 51.76 12.15 56.26 3.99 0.92 0.93 −0.012

KOUR −52.806 5.252 −4.68 12.05 0.06 0.48 0.88 0.90 0.037

LPGS −57.932 −34.907 −1.99 11.10 0.24 −0.28 0.83 0.81 −0.014

OHIG −57.9 −63.321 14.58 9.71 14.24 −1.67 0.98 0.98 0.008

RIOG −67.751 −53.785 3.27 11.59 2.28 0.84 0.88 0.90 −0.001

FUENTE:
Saludos,

 

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