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jueves, marzo 11, 2010

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:
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