Charles University Prague partner no. 16 (CUP) J. Zahradník, J. Janský, V. Plicka

Deliverables 12Data 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)

Deliverables 31 new vault for re-installation of CUP BB stations (WP1; UPATRA) Plan: SERG, 3-4 m deep excavation, pillar at the bottom, thermal insulation.

CMG-3T: 9 days in June, velocity no vault amplitude of the order of m/s

the same site after adding simple polystirin insulation improvement factor of 2

before and after thermal variation obvious, better insulation needed

Vartholomio earthquake Dec.2, :58 M=5.4 (PATNET)

BB: MAMO not equal SERG MAMO, D=94 km, A=66 o SERG, D=102 km, A=50 o M5.4 Vartholomio December 2, 2002

MAMO versus SERG MAMO, D=94 km, A=66 o SERG, D=102 km, A=50 o

at f < 0.1 we get rid of site effects MAMO 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)

Local event recorded at SERG Dec.10, :47 M 3.8 SERG: D=13 km A=84 o

3T problem at HF 5T problem at LF 3T almost clipped

Local M3.8 event: 3T needed to get f < 0.1 Hz M 3.8 recorded at D=13 km

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; 9 days “mass channel”, SERG

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 M3.5 earthquake

the anomaly consists of eqs. and 4-5 minute long pulses, m/s m/s 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. 3 23:42 and what happens during eq. ?

Mass channel

Velocity: signature of a sudden local tilt M km

Modeling a similar event Corinth Gulf M3, 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 the horizontal acceleration step of m/s 2 tilt step

The collocated CMG-5T accelerograph has the tilt pulse below its instrumental noise ! Anyway, CMG-5T is also needed for other purposes: Example: M3.8, 13 km (SERG)

Note the undisturbed vertical component, typical for the tilt. low pass f < 1 Hz: data model response

How about STS-2 (120-sec) ? STS-2, temporarily operated at the same station SER recorded some 300 local events, and 3 of them have had an analogous disturbance

Dec. 3 23:42

Mass channel

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

P. Bernard: The strain pulse of Dec. 3, 2002 is below the CMG-3T noise strain 10 -8, 10 km, 500 s m/s noise > m/s not too far !

Faster strain change can be seen easily right now “faster” ( < < 100 sec) = “sudden” for CMG-3T sudden strain increase = accel. step

Database (V. Plicka)

regional local transients

Deliverables 16New 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 M L 4.7 mainshock of the February-July 2001 earthquake sequence in Aegion, Greece. (J. of Seismology, 2004)

Zahradník, J., Janský, J., Sokos, E., Serpetsidaki, A., Lyon-Caen, H., and Papadimitriou, P. : Modeling the M L 4.7 mainshock of the February-July 2001 earthquake sequence in Aegion, Greece. (J. of Seismology, 2004) amplitude-spectra inversion Hz

Zahradník, J., Janský, J., Sokos, E., Serpetsidaki, A., Lyon-Caen, H., and Papadimitriou, P. : Modeling the M L 4.7 mainshock of the February-July 2001 earthquake sequence in Aegion, Greece. (J. of Seismology, 2004) inversion of the amplitude spectra Hz

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

M6 Lefkada earthquake Aug.14, BB stations epic.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

Two sources explain the Lefkada earthquake better than one black: one subevent red: two subevents SERG

Matching data by synthetics (4 subevents) and checking stability stability check: repeatedly removing 1 station

Checking stability of subevents (repeatedly removing one station) mom1=mom2=0.5e18 Nmmom3=mom4=0.2e18 Nm sub 4 is lesscertain

DC or non-DC ? Note that the two largest subevents have a slightly different focal mechanism. Their tensorial sum can mimic an apparently non-shear event. We have no indication about a true departure from 100% DC.

PROBLEMATIC NON-SHEAR MECHANISM OF MODERATE EARTHQUAKES IN WESTERN GREECE (ESC, Potsdam 2004) J. Zahradník, E. Sokos

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: data black: synthetics for 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 trial source position trial time shift

Repeating inversion with station removals: uncertainty assessment green: DC-percentage (with red ‘error bars’) blue: correlation

Very stable strike-dip-rake but highly unstable DC 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 their moment tensors: Result: sub 1+ 2 provides DC% 77 to 93%, analogous to the previous single-source study. Multiplicity seems to explain the non-DC mechanism.

The new trial fault plane is given by the patch (point 3) and the known strike (303 o ) old epicenter patch 5 trial source positions at each depth (16,17, and 18 km) the old epicenter now appears slightly off the plane (location error)

the subevent time separation is stable (2 + 2 sec), and the focal mechanism as well, incl. sub sec

The optimized “fault plane” stabilized the solution a lot. Sub 1,2,3 are not separated more than ~2 km from each other, but the delay is 2+2 seconds. = small distance, large delay. Rupture propag. with arrest ? A multiple event ! trial vertical plane 8 x 2 km removed station RLS VLS ITM EVR JAN KEK

RLS station: unfiltered data velocitydisplacement data model both NS, EW explained by an accel. step m/s 2 tilt

Restoration of normal seismic motion: = data minus model response green = blue - red data model response

Validation of the restored record through forward source modeling normalized displacement, band passed sec before removal after removal !! Only now the record can be used to study seismic source !! restored data synth. data

Near-fault seismic displacement has a static offset. Calculate it for nearby points, and get the strain and tilt. Example: RLS station (40 km from the M5 Vartholomio earthquake) the synthetics yield: permanent tilt = acc. step = m/s 2 but we observed the accel. step 3 orders of magnitude larger... SYNTHETIC TEST

Deliverables 95New software for near-real time seismic alarms (WP8) PEXT: perturbation and extrapolation finite-extent fault, composite source modeling deterministic envelopes and accel. spectral level, stochastic HF phase; perturbed HF radiation pattern

Colfiorito Mw 6.0 benchmark (M. Cocco)

forward station

... and backward station

“Moderate” directivity GTAD CTOR

Macroseismic observations: Alonnisos motion << Skyros motion (V. Karakostas)

Modeling strong motion based on weak-motion source model rupture propagation towards SE and the corresponding directivity effect

Athens 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 12Data base for selected stations of CUP (earthquakes + transients) 16 New software for source-parameter inversion (moment tensor, multiplicity) 95New software for near-real time seismic alarms (directivity, fast computations)