Soccoro Island

 

JoG: SOCA should not be used. Too few data

 

IDS: SOCA should not be used. Too few data

 

JoG SODA data should be deleted from 01-JAN-1990 to 01-JAN-1996

NB: Non linear motion, due to volcanic subsidence (see AC)

 

JoG break on 03-OCT-2002

Earthquake

PW: In fact, there was no Earthquake at this period, but the break is real

 

IDS: break on 03-OCT-2002

Earthquake

 

ITRF SODB break on 03-OCT-2002

 

Preliminary computations:

 

Using new study that supersedes all previous determinations.

 

P. Briole, P. Willis, J. Dubois, O. Charade, Potential volcanological applications of the DORIS system, A geodetic study of the Socorro Island (Mexico) coordinate time series, Geophys. J. Int., in press

 

From, this document the station velocity can be expressed (in ITRF2000) as follow

 

Acronym

Period

VN (mm)

ITRF2000

VE (mm)

ITRF2000

VU (mm)

ITRF2000

Comment

SOCA

... - ...

20.5

-54.6

0.0

 

SODA

 ... – 2/1/1993

20.5

-54.6

0.0

 

SODA

3/1/1993 – 26/12/1995

118.8

-95.4

-93.9

 

SODA

27/12/1995 - ...

14.7

-43.7

-1.2

 

SODB

... – 2/10/2002

14.7

-43.7

-1.2

Discontinuity at 03/10/2002

SODB

3/10/2002

20.5

-54.6

0.0

 

 

The discontinuity at 03-OCT-2002 was estimated as N -44.1, E +67.4 V -5.9 mm

 

From this, we obtain (in XYZ, still in ITRF2000)

 

 

Acronym

Period

VX (mm)

ITRF2000

VY (mm)

ITRF2000

VZ (mm)

ITRF2000

Comment

SOCA

... - ...

-48.6

25.7

19.4

 

SODA

 ... – 2/1/1993

-48.6

25.7

19.4

 

SODA

3/1/1993 – 26/12/1995

-43.7

152.8

82.4

 

SODA

27/12/1995 - ...

-38.7

21.1

13.5

 

SODB

... – 2/10/2002

-38.7

21.1

13.5

Discontinuity at 03/10/2002

SODB

3/10/2002

-48.6

25.7

19.4

 

 

The discontinuity at 03-OCT-2002 was estimated as X 59.9 Y -32.1 Z -43.7 mm

 

We then obtain in ITRF2005 (by transformation from TRF2000 to ITRF2005)

 

 

Acronym

Period

VX (mm)

ITRF2005

VY (mm)

ITRF2005

VZ (mm)

ITRF2005

Comment

SOCA

... - ...

-49.0

24.0

21.3

 

SODA

 ... – 2/1/1993

-49.0

24.0

21.3

 

SODA

3/1/1993 – 26/12/1995

-44.1

151.1

84.3

 

SODA

27/12/1995 - ...

-39.1

19.4

15.4

 

SODB

... – 2/10/2002

-39.1

19.4

15.4

Discontinuity at 03/10/2002

SODB

3/10/2002

-49.0

24.0

21.3

 

 

The discontinuity at 03-OCT-2002 was estimated (in ITRF2005) as X 59.5 Y -32.0 Z -44.0 mm

 

The value that we will adopt here is (in XYZ): +60 -32 -44 mm

 

We first compute the SODB value in ITRF2005 at epoch 2000.0 using the last set of data (after 03-OCT-2002) and fixing the velocity to -49.0 24.0 21.3, we then obtain :

 

For SODB (3/10/2002 to ...)

 

2000.0 SODB -2160725.5137 -5643017.4793 2034836.9607 -49.00 24.00 21.30

statistics SODB XYZ 0.0012 0.0009 0.0011 301

 

We will start with this solution and go backward in time

 

At epoch 2002.75, using the velocity -49.00 24.00 21.30, we obtain for 03-OCT-2002 (after the break)

 

2002.75 SODB -2160725.649 -5643017.413 2034836.965 -49.00 24.00 21.30

 

so before the break, the position in 2002.75 was :

 

2002.75 SODB -2160725.709 -5643017.381 2034837.009 -49.00 24.00 21.30

 

From, this position, using the velocity from the period ... – 2/10/2002 (-39.1 19.4 15.4), we obtain the position at epoch 2000.0 for this period :

 

2000.0 SODB -2160725.603 -5643017.434 2034836.967 -39.1 19.4 15.4

 

As a confirmation, when using the available DORIS data and fixing the velocity to -39.1 19.4 15.4, I get at epoch 2000 :

 

2000.0 SODB -2160725.5823 -5643017.4470 2034836.9959 -39.10 19.40 15.40

statistics SODB XYZ 0.0035 0.0030 0.0028 94

 

so it confirms the determination above.

 

The last data of SODA and the first data of SODB, so we can directly use the geodetic local information at epoch 2000

 

Local tie is

 

SODB 40503S004 SODA 40503S003 0.089  0.233 -0.084 0.001

 

So, we get

 

2000.0 SODA -2160725.514 -5643017.201 2034836.883 -39.1 19.4 15.4

 

To get a confirmation, we can use the last SODA data (after 1996) and fix the velocity, we obtain :

 

2000.0 SODA -2160725.4735 -5643017.2230 2034836.9038 -39.10 19.40 15.40

statistics SODA XYZ 0.0039 0.0027 0.0030 92

 

so, it is a rather good confirmaton

 

From, the proposed position/velocity, we can obtain the position in 1996.0, using the same velocity during this interval :

 

1996.0 SODA -2160725.358 -5643017.279 2034836.821 -39.1 19.4 15.4

 

As a verification, I can use the SODA weekly solution (obtained in ITRF2000), at epoch 1996.0 a mean value was :

 

1996.0 SODA -2160725.302 -5643017.303 2034836.867 (in ITRF2000)

 

so, when transformed into ITRF2005, we obtain

 

1996.0 SODA -2160725.322 -5643017.284 2034836.876 (in ITRF2005)

 

we have then a reasonably good confirmation of the coordinates that is compatible with the POD goal.

 

so, using the correct velocity during this period for SODA (1993.0 - 1996.0), we obtain:

 

2000.0 SODA -2160725.534 -5643016.675 2034837.158 -44.1 151.1 84.3

 

On Jan, 1, 1993, the position is then

 

1993.0 SODA -2160725.225 -5643017.733 2034836.568 -44.1 151.1 84.3

 

to verify, we can use the STCD time serie (in ITRF2000), after some smoothng, we get at epoch 1993.0

 

1993.0 SODA -2160725.185 -5643017.772 2034836.589 (in ITRF2000)

 

so, when expressed in ITRF2005, from the DORIS results, we get :

 

1993.0 SODA -2160725.205 -5643017.753 2034836.598

 

we then have a good verification of our model

 

so for the 1991.0 – 1993.0 period, we have (expressed at epoch 1993.0)

 

1993.0 SODA -2160725.225 -5643017.733 2034836.568 -49.0 24.0 21.3

 

so, if we express the model at epoch 2000.0, we obtain

 

2000.0 SODA -2160725.568 -5643017.565 2034836.717 -49.0 24.0 21.3

 

As SOCA and SODA have the same velocity at the beginning, we can the geodetic local tie directly at epoch 2000.0

 

The geodetic local tie is

 

SODB 40503S004 SOCA 40503S002 -202.883 30.460 -148.559 0.03

SODB 40503S004 SODA 40503S003 0.089  0.233 -0.084 0.001

 

So, we derive

 

SODA 40503S003 SOCA 40503S002 -202.972 30.227 -148.475 0.03

 

From, the geodetic local tie and the SODA position (1991.0-1993.0), we obtain:

 

2000.0 SOCA -2160728.540 -5642987.338 2034688.242 -49.0 24.0 21.3

 

To verify, this number, we can use DORIS results (in ITRF2000) at the mid epoch of observations = 1990.4

 

1990.4 SOCA -2160928.038 -5642987.638 2034688.099 (in ITRF2000)

 

by transforming into ITRF2005, we get :

 

1990.4 SOCA -2160728.058  -5642987.619  2034688.108  (in ITRF2005)

 

Our model was:

 

2000.0 SOCA -2160728.540 -5642987.338 2034688.242 -49.0 24.0 21.3

 

so, when expressed in 1990.4, we obtain :

 

1990.4 SOCA -2160728.070 -5642987.568 2034688.038 -49.0 24.0 21.3

 

So the agreement is rather good, except in Z, but is compatible with the geodetic local tie precision and with the required accuracy for POD

 

Recommendation:

 

SODB break on 03-OCT-2002

 

We can now use all data from the Socorro Island

 

 

2000.0 SOCA -2160728.540 -5642987.338 2034688.242 -49.0 24.0 21.3

 

 1991.0 – 1993.0

2000.0 SODA -2160725.568 -5643017.565 2034836.717 -49.0 24.0 21.3

 

1993.0 – 1996.0

2000.0 SODA -2160725.534 -5643016.675 2034837.158 -44.1 151.1 84.3

 

1996.0 –

2000.0 SODA -2160725.514 -5643017.201 2034836.883 -39.1 19.4 15.4

 

... – 2002.75

2000.0 SODB -2160725.603 -5643017.434 2034836.967 -39.1 19.4 15.4

 

 

2002.75 - ...

2000.0 SODB -2160725.5137 -5643017.4793 2034836.9607 -49.00 24.00 21.30