NEAREST WP3 meetingBerlin 8tth October 2008, Technische Fachhochschule Berlin

Seismic data from GEOSTAR

Stephen Monna and Francesco FrugoniI.N.G.V. - Rome

Presentation overview

Data statistics

Signal qualityDisturbancesPossibility to “cure” disturbances

Data examples

Conclusions

GURALP CMG-40T 3 component broadband seismometer (30 s-50 Hz)

GURALP CMG-5T 3 component broadband accelerometer, strong motion (DC-100 Hz)

OAS E-2PD- Hydrophone 0- 5KHz

100 Hz sampling, 7 channels 24 bit + 3 mass channels 16 bit

GURALP DM-24 Digitizer, 7 channels at 24 bit + 3 auxiliary OBS mass channels at 16 bit

synchronization from SERCEL rubidium clock- input in GPS DM-24 channel

MCU restarted day 53 (17 October 2007)

Number of bytes recorded/day for OBS, ACC, HYD

For OBS: 2.22*10^4 over 2.34*10^4 Mbytes = 95 % of expected bytes recorded

21 August 2007- Port of Faro, Portugal

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

Time 200 s

Recording 7 channels before deployment

First recording period after deployment 7 channels25 August 2007

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

Time 200 sHydrophone breakdown

145 s period disturbance

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

25 August 2007 First 80 s after deployment

Time 10 s

Detail- hydrophone breakdown, note the corresponding step on ACC

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

Time 10 s

25 August 2007

Hydrophone- comb-style waveform starts25 August 2007

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

Time 100 s

Example 1 hour recording for all 7 channels

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

Time 500 s

06 March 2008

06 March 2008

OBS-E

OBS-Z

OBS-N

ACC-Z

ACC-N

ACC-E

HYD

Zoom on 145 s period disturbance

Time 20 s

This signal form strongly suggests leveling of the sensors is going on

Zoom on 145 period disturbance- onset

OBS-ZMass

OBS-Z

ACC-Z

HYD

Time 0.5 s

1 hour FFT, OBS-Z component

Fundamental frequency 7mHz ---> 145 s period

2 time series, 1 hour long. OBS-Z component

Can we “clean” the signal ?”

auto-correlation and cross-correlation on the 2 previous series

145 s

amplitude

Time

AUTO

CROSS

Example of 145 s time series which includes the disturbance, used to “clean” the signal

Effect of simple cleaning procedure, teleseismic event Mw6.9 N-mid atlantic ridge

Onset first P-arrival 1 Hz, at 9:45:40 (no drift correction)

Arrival at Portuguese land station PFVI (100 km from GEOSTAR ), 9:45:477 s difference is in agreement with P traveltime tables for shallow eventsClock drift for the whole mission is 184 ms in 359 days ---> ~ 0.51 ms/day

time10 s

before

after

time 5 s

Signal cleaning example for a very local event (not present on local seismic bulletins)

before

after

Onset P arrival

Bandpassed 4-20 Hz 4 poles, butterworth

11 January 2008

OBS-Z

OBS-N

OBS-E

local event ( ~50 km), Ml4.4, unfiltered traces

Example data recorded