1 / 17

Václav Vavryčuk , Fateh Bouchaala, Tom áš Fischer Institute of Geophysics, Prague

High-resolution fault tomography from accurate locations and focal mechanisms of swarm earthquakes. Václav Vavryčuk , Fateh Bouchaala, Tom áš Fischer Institute of Geophysics, Prague. West-Bohemia n earthquake swarm in 2008. Seismicity in West Bohemia, Czech republic. Data and methods.

satin
Download Presentation

Václav Vavryčuk , Fateh Bouchaala, Tom áš Fischer Institute of Geophysics, Prague

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. High-resolution fault tomography from accurate locations and focal mechanisms of swarm earthquakes Václav Vavryčuk, Fateh Bouchaala, Tomáš Fischer Institute of Geophysics, Prague

  2. West-Bohemian earthquake swarmin 2008

  3. Seismicity in West Bohemia, Czech republic

  4. Data and methods Data • 249 selected micro-earthquakes from the 2008 swarm • Magnitudes between 0.5 – 3.7 • Depth between 7 and 11 km • 18-22 local short-period seismic stations • Good focal coverage • Sampling rate 250 Hz • Epicentral distance up to 40 km Method • Double-difference location method • P and S wave arrivals obtained using cross-correlation • Frequency-domain waveform inversion for moment tensors • P waves • 1-D smooth model • Ray-theoretical Green’s functions

  5. Locations: map view main active fault main active fault 4 km 2 km

  6. Waveform inversion of P waves event X1613A

  7. Examples of focal mechanisms Waveform inversion of P waves good focal sphere coverage, slightly non-DC mechanisms

  8. Variety of focal mechanisms 249 most accurate focal mechanisms Nodal lines P/T axes o P axis, + T axis three basic types of focal mechanisms

  9. Locations & focal mechanisms: map view main active fault main active fault 4 km most frequent focal mechanism 2 km

  10. Fault segmentation: depth sections cross section 1 in-plane section 1 2 1 2 2 4 km 3 4 3 3 5 4, 5 4 5 4 km 2 km

  11. Foci clusterings & focal mechanisms cross section 1 1 + 2 2 + 3 + 5 5 3 4 + 4 + 2 km o fault normals from focal mechanisms, + fault normal from clustering of foci

  12. Inversion for stress: Angelier method (2002) Fit function SSSC criterion is maximized σ2 x Principal stress axes 1 and 2 are inclined σ3 o σ1 + Optimum stress:

  13. Definition of the fault stability Mohr’s circle diagram

  14. Fault instability & focal mechanisms Fault instability Fault instability& fault normals σ2 x misoriented faults optimally oriented faults σ3 o σ1 + optimally oriented faults 3 4 2 1

  15. Fault instability & Mohr’s diagrams Mohr’s diagrams optimally oriented faults misoriented faults low shear stress Fault instability σ2 σ3 σ2 σ1 x σ3 o σ1 + σ1 σ3 σ2 high shear stress optimally oriented faults σ3 σ2 σ1

  16. Conclusions main active fault • complex geometry of active faults • – rough and curved surface • – fault segments with a different orientation • clustering of foci almost exactly coincides • with focal mechanisms • two fault systems are optimally oriented • with respect to stress (principal faults) • misoriented faults segments with low • shear stress are also activated σ1 left-lateral 4 km right-lateral

More Related