Three BB and SM seismic stations in the Corinth Gulf

jointly operated by the universities in Prague and Patras

Jiri Zahradnik

Charles University, Prague

Co-operation:

G-A. Tselentis, E. Sokos,

A. Serpetsidaki

V. Plicka, J. Jansky

Sergoula, Mamousia, University

• CMG 3T BB vel

• CMG 5T SM acc

• DM24 + SAM

• 20 Hz continuous

• 100 Hz triggered

• stand-alone

• 3-5 months

Sergoula, Mamousia, University

• CMG 3T BB vel

• CMG 5T SM acc

• DM24 + SAM

• 20 Hz continuous

• 100 Hz triggered

• stand-alone

• 3-5 months

April 8, 2001SERG

black=obs.red=synth.

My “normal” jobis modeling, buttoday I want to discuss the datareliability.

Are our data accurate ?

• Compare the instrumentally corrected records, sampling 100 Hz (5T accel. and the differentiated 3T)

• Demonstrate complications

velocityacceleration

Zeros and poles fromfactory calibration tests

Vartholomio earthquake

• Dec.2, 2002

• 04:58

• M=5.4 (PATNET)

• Mw=5.6 (MEDNET)

VartholomioDec. 2, 2002

M 5.4at MAMO

(94 km)

3T clipped(2 mm/sec)

3T clipped(2 mm/sec)

ZOOM

MAMO

clipped 3T viewed as non-clipped acceleration(suggesting a method how to correct clipping)

MAMO

with the clipped part

without

Noise (natural and instrumental)

microseisms resolved by 3T, but not resolved by 5T

MAMO

Minimum frequency available from the 5T accelerograph (M 5.4; 94 km)

Vartholomio earthquakeM 5.4

at SERG (102 km)

Vartholomio earthquakeM 5.4

at SERG (102 km)

temporaryGPS (digitizer)problem

SERG

fit in EW asgood as in Z(3T || 5T)

some HF noise ?

SERG

velocitynot clipped

velocity in SERG is lower than in MAMO,but acceleration is SERG is higher

SERG

a significant HF ‘ringing’ of 3T(not caused by clipping)

ZOOM

SERG

SERG

Local event recorded at SERG

• Dec.10, 2002

• 16:47

• M 3.8

• SERG:

D=13 km

A=84o

Local M 3.8 at SERG(13 km)

Local M 3.8 at SERG

(13 km)

less problems onthe Z-comp. of 3T,both in HF and LF

Too noisy LF signal on 5T even at f ~ 0.1 Hz

M 3.8 recorded at D=13 km

Local event recorded at SERG

• Nov. 13, 2002

• 21:55

• M 3.0

• SERG:

D=7.5 km

A=51o

SERGNovember 13, 2002; at 21:55; M 3

SERG: D=7.5 km, A=51o

NS-comp. of 3T velocity EW-comp. of 3T velocity

a rare disturbance(signal-generated)

occasionally,the LF signal on 3T is “as bad” as on 5T !

LF

the LF signal on Z-comp. of 3T is OK

M 3 at SERG

(7 km)

HF noise on horizontalcomponents of 3T

Local event recorded at UNIV

• Nov. 26, 2002

• 12:13

• M 3.5

• UNIV:

• D=13 km

• A=209o

Nov. 26, 2002M 3.5

at UNIV(13 km)

Nov. 26, 2002M 3.5

at UNIV(13 km)

GPS problem

Local event recorded at UNIV

• Apr. 18, 2003

• 12:49

• M 2.5

• UNIV:

D=5 km

A=126o

April 18, 2003 M 2.5

at UNIV (5 km)

GPS recovered “itself”

April 18, 2003 M 2.5

at UNIV(5 km)

HF instrumental noise in 3TLF instrumental noise in 5T(complementary)

Conclusion

• joint deployment of 3T BB and 5T SM revealed problems of both instruments

• HF noise peak (30 Hz) on horiz. comp. of 3T

• white accel. noise of 5T

• occasional disturbances on horiz. 3T (tilt ?)

• temporary timing (GPS, digitizer) problems

Instrumentally “corrected” records are rarely correct

to every detail.

Joint deployment of

the 3T (BB) and 5T (SM) helps to reveal problems, and the instruments

complement each other.

All data available fromhttp://seis30.karlov.mff.cuni.cz

Thank you !