Charles University PragueCharles University Praguepartner no. 16 (CUP)partner no. 16 (CUP)

J. Zahradník, J. JanskJ. Zahradník, J. Janský, V. Plickaý, V. Plicka

Deliverables

12 Data base for selected stations of CUP (WP1)

Plan:attention to “classical” issues(location, focal mechanisms, strong motions)as well as various transients possibly related to strain

Present status: 8 CUP instruments jointly operated with UPATRAS

at 4 sites

• 2 stand-alone (SERG, MAMO)

• 2 satellite (LOUT, PYLO)

• each one with CMG-3T and 5T (weak & strong)

SERG (Sergoula)

MAMO (Mamousia)

BB: MAMO not equal SERG

MAMO, D=94 km, A=66o

SERG, D=102 km, A=50o

M5.4 VartholomioDecember 2, 2002

at f < 0.1 we get rid of site effectsMAMO SERG

5T as good as 3T for M5.4

Both CMG-3T and CMG-5T are needed (even for small local

events):

Example: M3.8, 13 km (SERG)

3T problem at HF

5T problem at LF

3T almost clipped

Can we also contribute to studies of slow strain events ?

Example: December 3, 2002 (suggested by Pascal B.)

• lower thermal variation in winter

• velocity record supplemented by

“mass channel” (integrated velocity output)

CMG-3T 3 days “mass channel”: an anomaly superimposed on the

thermal variation

EW NS

Zooming anomaly on EW (1 day)

... and the corresponding velocity

increased noise ?

anomaly

M3.5earthquake

the anomaly consists of eqs. and 4-5 minute long pulses, 10-5 m/s

4 10-6 m/s

10-5 m/s

CMG3-T: 1 day (Dec. 3, 2002)

Just these 4-5 minute long pulses constitute the anomaly of the mass

channel.

M3.5

Dec. 323:42

and what happensduring eq. ?

Mass channel

Velocity: signature of a sudden local tilt

M3.510-20 km

Modeling a similar event

Corinth GulfM3, distance 10km

Normal instrument response of CMG-3T to abnormal input:

ACCELEROGRAPH 100-SEC VELOCIGRAPH

input

output

input

output

Modeling the CMG-3T response

we arrive at thehorizontal acceleration stepof 6.10-6 m/s2

tilt step 6.10-7

Note the undisturbed vertical component, typical for the tilt.

low pass f < 1 Hz:data

model response

Dec. 323:42

5 min !

Following the sudden tilt (< 100 sec), accompanying the earthquake,there is a slow “strain recovery” but its amplitude is 10-30 smaller than slow pulses accompanyingthe preceding burst of smaller eqs.

Database (V. Plicka)http:/seis30.karlov.mff.cuni.cz

Database (V. Plicka)http:/seis30.karlov.mff.cuni.cz

regional local transients

Deliverables

16 New software for source-parameter inversion (WP1)

Innovation:LF local waveforms (f < 0.1 Hz)moment tensor, uncertainty of non-DC, multiplicity in space and time synthetic and/or empirical Green fctn.

Zahradník, J., Janský, J., Sokos, E., Serpetsidaki, A.,Lyon-Caen, H., and Papadimitriou, P. :Modeling the ML4.7 mainshock of the February-July 2001earthquake sequence in Aegion, Greece. (J. of Seismology, 2004)

inversion ofthe amplitude spectra 0.1 - 0.2 Hz

Iterative deconvolution of regional waveforms

Zahradník, J., Serpetsidaki, A., Sokos, E., Tselentis, G-A.:Iterative deconvolution of regional waveforms anddouble-event interpretation of the 2003 Lefkadaearthquake, Greece (Bull. Seism. Soc. Am., in press)

M6 Lefkada earthquakeAug.14, 2003

5 BB stationsepic.distance<140 km

Method• moment-tensor inversion (minimization of the L2

waveform misfit by the weighted least-square method)

• optimization of the source position and time (maximization of the correlation by the space-time grid search)

• a single point source for f < 0.1 Hz, and multiple point sources for f < 0.3 Hz

Final solution: 2 main

subevents,40 km and 14 sec apart

explaining the two aftershock

clusters

Vartholomio (near Zakynthos)

Dec. 2, 2002

ETH-SED: Mw=5.7

DC%=55 !(HRV: DC%=58,

Mednet: DC%=44) Zakynthos

6 NOA stations, f=0.05 to 0.1 Hz

weights proportional to 1/A were applied

blue: datablack: syntheticsfor crustal model of Haslinger et al. (1999)

100% DC matches data also well(only 0.05 worse)

we cannot see the difference

Going into large details: Optimum correlation

is not compatible

with 100% DC

tria

l sou

rce

posi

tion

trial time shift

Very stablestrike-dip-rakebuthighly unstableDC percentage

DC%: 72 to 97 %cf. 55% (ETH)

Fixing the opt. source position and increasing frequency (f < 0.3 Hz): 3 subevents

2-sec time delay between sub 1 and 2; sub 3 is unstable

Subevents 1 and 2: similar strike and dip, but different rake

Consider sub 1 and 2 as 100% DC(but unequal !), and sum up theirmoment tensors:

Result: sub 1+ 2 provides DC%77 to 93%, analogous to the previous single-source study.

Multiplicity seems to explainthe non-DC mechanism.

Deliverables

95 New software for near-real time seismic alarms (WP8)

PEXT: perturbation and extrapolationfinite-extent fault, composite source modelingdeterministic envelopes and accel. spectral level,stochastic HF phase; perturbed HF radiation pattern

Colfiorito Mw 6.0 benchmark

(M. Cocco)

“Moderate” directivity

GTAD

CTOR

Athens 1999 - PGA modeling

Shake map

up to 20 Hz

in a few minutes

on a PC

Tuning maximum slip velocity against the attenuation relation

Athens - synth. versus real records

... another station

Charles University Prague (CUP) summary of the tasks

12 Data base for selected stations of CUP (earthquakes + transients)

16 New software for source-parameterinversion (moment tensor, multiplicity)

95 New software for near-real time seismic alarms (directivity, fast computations)

http:/seis30.karlov.mff.cuni.cz