1. Disputable non-DC components of several strong earthquakes Petra Adamová Jan Šílený

2. Motivation  For some strong events a large non-DC component is reported by agencies  This component is often questionable (large events, tectonic origin)  it can be false due to source finiteness (strong event is modeled as point source)

3. Introduction to second degree moments Standard moment tensor Point source: couple of planes  a ‘dot’

4. Introduction to second degree moments “Finite source” parameters from point source approximation Detailed modeling of slip on the fault plane: - costly - often data not available (near the fault) 2 nd degree moments are advantageous alternative geometry of the source duration of the source process average slip on the fault spatial and temporal centroid rupture velocity vector  Inside the ‘dot’

5. Theory Moments till degree 2, Doornbos (1982) Temporal centroid Spatial centroid Source ellipsoid Rupture propagation Source process duration Zero degree moment tensor (standard MT)

6. Inverse scheme: full waveform inversion exclusion of the non-physical solutions  inversion is faster Standard MT Estimation of second degree moments

7. Applications: Location of earthquakes

8. Standard focal mechanisms zero degree moments

9. Jack-knife test - Izmit and Kobe

10. Kobe – 2 nd degree moments Ide et al. (1996) 10 km

11. Example of seismogram fit Black: observed seismograms Red: synthetic seismograms

12. Izmit – 2 nd degree moments Clevede et al. (2004)

13. Synthetic experiment: Estimate of error due to noise for the Izmit earthquake 5 samples of random noise of 20% and 30% of maximum amplitude superimposed on the records   Level 20%: stable solution, small deviation, for source ellipsoid orientation – max. deviation 5 degrees Level 30%: unstable solution, large deviation for source ellipsoid orientation – max. deviation 17 degrees Black ellipsoid: extreme deviation with 20 % noise Blue ellipsoid: extreme deviation with 30 % noise

14. Focal mechanisms Standard MT Standard MT without second degree effects computing standard MT estimation of 2 nd degree moments removing 2 nd degree moments from the data computing new standard MT

15. Conclusions Second degree moments bring additional information above standard MT: source ellipsoid, duration of the source process, average rupture velocity Neglect of source finiteness, which remains in the data even after an essential low-pass filtering may originate spurious non-DC components in the mechanism. The procedure suggested reduces spurious non-DC components substantially