The Mw 6.3 Movri The Mw 6.3 Movri Mountain earthquake, Mountain earthquake, June 8, 2008, GreeceJune 8, 2008, Greece

Sokos E.1, Serpetsidaki A. 1, Tselentis G. 1, Gallovic F. 2, Krizova D. 2, Plicka V. 2, Zahradnik J. 2

1Department of Geology, Seismological Laboratory, University of Patras, Greece

2 Charles University in Prague, Czech Republic

The M6 event of the 2008 ‘storm’ of strong earthquakes in Greece

Papadopoulos, G. A., V. Karastathis, M. Charalambakis, A. Fokaefs (2009). A Storm of Strong Earthquakes in Greece During 2008, Eos Trans. AGU, 90, 425–426.

ITSAK: http://www.itsak.gr/news/categories/24

•Significant event•Extensive damage•Two victims•Hundreds of injuries

DAMAGING EFFECTS

Strike slip

Depth ~ 20km

Relatively rare eventof this size (Mw 6.3)in NW Peloponnese

REGIONAL FRAMEWORK

CMT - http://www.globalcmt.org/CMTsearch.html

GEOLOGY - TECTONICS

• Μain geological formations are flysch and limestone; parts of Pindos and Gavrovo isopic zones

• The main tectonic feature is the ~NS trending Scolis thrustKoukouvelas et al., 2009, IGR

•Epicenter located between villages Dafni and Michoi

•The activated zone clearly proves the SW-NE fault plane

•Similar results obtained by Ganas, et.al 2009, JEE.

•No clear relation of fault plane to mapped surface faults (blind event, depth ~20 km)

(Red lines are co-seismic ruptures, Koukouvelas et al., 2009, IGR)

INITIAL LOCATION

RELOCATION OF THE SEQUENCE (HYPODD)

RELOCATION OF THE SEQUENCE (HYPODD)FIRST DAY SEISMICITY

SW NE

RELOCATION OF THE SEQUENCE (HYPODD)

Two clusters

North: M < 4.4~30 events M3within 13 hoursafter mainshock

RELOCATION OF THE SEQUENCE (HYPODD)

Two clusters

North: M < 4.4~30 events M3within 13 hoursafter mainshock

South: M < 3.3first M>3 only13 hours aftermainshock

PSLNET BB and SM (SER, MAM, LTK, PYL co-operated by Charles Univ.)

ITSAK SM NOA BB

Near-regional stations

Frequency < 0.2 Hz

SOURCE INVESTIGATION (MAINSHOCK)

CENTROID AND HYPOCENTER

HC

Centroid position as a part of the CMT solution(ISOLA software; Sokos and Zahradnik, 2008)

C at about 8 km from Htoward NE

Indicationof the rupture propagationtoward NE

• ISOLA code modified to prevent a highly concentrated slip (Zahradnik et al., JGR, in press)

• a new technique (Gallovic et al., GRL 36, L21310, 2009), iterative back-propagation of the waveform residuals by the conjugate gradients technique

The two methods do not need

prior knowledge of the nucleation point and rupture velocity.

SLIP INVERSION: TWO METHODS

TWO METHODS – SIMILAR RESULTS

Color: the new iterative back-propagation method

Green circles: ISOLA modified for distributed slip

TWO METHODS – SIMILAR RESULTS

Color: the new iterative back-propagation method

Green circles: ISOLA modified for distributed slip

Caution: Time versus Distance(a 1D model, not 2D)

TWO METHODS – SIMILAR RESULTS

Predominant unilateral rupture propagation

along strike (toward NE)

Two-three main patches, mutually delayed by almost

5 seconds

Delay of the first patch with respect to origin time

(inversion assuming Vr=const from H would fail !) Possible temporary rupture arrest.

H

Examples of slip models equally well matching real waveforms (variance reduction 0.7)

Black circles: an (assumed) patchused to initializethe inversion.

More details in oral presentation by Zahradnik and Gallovic (session ES5, Thursday morning)

CAUTION ! The result is inherently non-unique.

LINE SOURCE MODEL AND ITS RELATION TO AFTERSHOCKS

Recallthe two aftershock clusters.

LINE SOURCE MODEL AND ITS RELATION TO AFTERSHOCKS

Recallthe two aftershock clusters.

Main slip released betweenthe two clusters.

LINE SOURCE MODEL AND ITS RELATION TO AFTERSHOCKS

Recall also different propertiesof the two clusters –

related to the predominant rupture propagationtoward NE

CONCLUSIONS

Accurate relocation, combined with the near-regional, low-frequencyslip inversion explained rough history of the mainshock and the sequence.

Accurate relocation, combined with the near-regional, low-frequencyslip inversion explained rough history of the mainshock and the sequence.

Relatively large depth (~20 km) hampered resolution of the slip along fault dip(other authors published the 2D slip, e.g. . Konstantinou et al., BSSA 2009).

Line-source model (along strike) proved sufficient to recognize main featuresof the rupture propagation.

CONCLUSIONS

Accurate relocation, combined with the near-regional, low-frequencyslip inversion explained rough history of the mainshock and the sequence.

Relatively large depth (~20 km) hampered resolution of the slip along fault dip(other authors published the 2D slip, e.g. . Konstantinou et al., BSSA 2009).

Line-source model (along strike) proved sufficient to recognize main featuresof the rupture propagation.

The earthquake led to development of two inversion methods, independent of the prior knowledge of the nucleation point and rupture velocity.

The source model indicated a few patches with mutual delays; they might have important implication for strong ground motions (a special study needed).

CONCLUSIONS

Accurate relocation, combined with the near-regional, low-frequencyslip inversion explained rough history of the mainshock and the sequence.

Relatively large depth (~20 km) hampered resolution of the slip along fault dip(other authors published the 2D slip, e.g. . Konstantinou et al., BSSA 2009).

Line-source model (along strike) proved sufficient to recognize main featuresof the rupture propagation.

The earthquake led to development of two inversion methods, independent of the prior knowledge of the nucleation point and rupture velocity.

The source model indicated a few patches with mutual delays; they might have important implication for strong ground motions (a special study needed).

Importance of the NE source directivity for hazard assessment of Patras.

CONCLUSIONS