1 / 29

Small-aperture array at Dobrá Voda: first records of local earthquakes

Small-aperture array at Dobrá Voda: first records of local earthquakes. Jiří Málek, Milan Brož and Jaroslav Štrunc Institute of Rock Structure and Mechanics AS CR, Prague, Czech Republic, malek@irsm.cas.cz. Second annual meeting Advanced Industrial Microseismic Monitoring AIM

arabela-eddery
Download Presentation

Small-aperture array at Dobrá Voda: first records of local earthquakes

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. Small-aperture array at Dobrá Voda: first records oflocal earthquakes Jiří Málek, Milan Brož and Jaroslav Štrunc Institute of Rock Structure and Mechanics AS CR, Prague, Czech Republic, malek@irsm.cas.cz Second annual meeting Advanced Industrial Microseismic Monitoring AIM Prague 29-30.9.2011

  2. Contents • Small-aperture seismic arrays (SSA) for microseismic monitoring • SSA Dobrá Voda • Tests - records of distant earthquakes • Records of local earthquakes • Examples from other SSA operated by IRSM • Future plans

  3. Small-aperture seismic array (SSA) for microseismic monitoring • Detection of very weak earthquakes: local shallow earthquakes M>-1.5 can be detected • Detection of (non-volcanic) tremors, recognition from industrial noise • Recognition of new phases on the seismograms of local earthquakes • Measurements of rotational components of seismic waves • Volcanic seismology – seismic antennas

  4. Small-aperture seismic array (SSA) for microseismic monitoringSpecial features: • High frequencies (10 – 30 Hz) • Small aperture (50 – 120 m) • Only several stations (IRSM – 4 stations 3C)

  5. SSA’s built by IRSM AS CR • OSTA – Eastern Bohemia – Hronov-Poříčí Fault (2005) • NKCA – Western Bohemia – Seismic swarms (2007) • PROA – Provadia (Bulgaria) – Induced seismicity (2009) • LAZA – Western Bohemia – Seismic swarms(2011) • DOVA – Little Carpathians – (2011) – AIM project

  6. Optimal dimensions • Signals have to be coherent – small aperture • Time differences between stations should be significant – bigger aperture • Our recommendation: aperture is equal to wave-length / 4 of the typical signal Va=8 km/s, F= 20 Hz => A=100 m

  7. P-wave group, NKCA, shifted seismogramsOptimal azimuth (130°) and apparent velocity (15 km/s)

  8. P-wave group, NKCA, shifted seismogramsWrong azimuth (310°) and apparent velocity (15 km/s)

  9. Linear and non-linear stacking of coherent signals • To determine azimuth and aparent velocity f-k analysis is normally applied • Alternatively, we use optimization of stacked seismograms in time domain. • Linear or non-linear filters can be used • A new method GAS (Generalized Average Method) was developed and applied

  10. Generalized average of signals

  11. Dobrá Voda Array (DOVA) was built around the DOV (MKNET) station at the main epicentral zone of the Malé Karpaty region • DOVA consists of 3 short-period three-component stations: D1V, D2V, D3V • Distance between stations is 120 m • Central station Guralp-5s (sampling 100 Hz), other stations Le3D-1s (sampling 250 Hz) • Registration started on May17, 2011

  12. Test 1, Fiji, h=599km, mb=5.8 PKIKPVa > 100 km/s DOVA

  13. Test 2, Japan, mb=6.2 P DOVA

  14. Test 2, Japan, mb=6.2 P DOVA Rotational components ?

  15. New Portable Mechanical Sensor System for Rotational Seismic Motion Measurements 2nd IWGoRS Workshop, Prague, 10 – 13 October 2010 Rotaphone - basic features: Brokešová et al. 2010 It consists of highly sensitive geophones, measuring reliably in the range 2 – 100Hz, connected to a common recording device (amplifier, transducer, etc.); The geophones are mounted in diametrical pairs to a rigid ground-based undeformable (metal) skeleton; The distance separating the geophones in the given pair is much smaller than l but sufficiently large to allow the differential motions to be detected; The instrument provides records of translational seismic motions together with rotations; Rotation rate is determined by more than one geophone pair, which allows to perform 'in situ' calibration of the geophones simultaneously with the measurement.

  16. Local Earthquake N from Piestany, 20.7.2011 18:31:00.9 48.65 N17.89 E Depth: 2kmML=1.8 (GFU SAV)

  17. DOVA P S

  18. Earthquake N from Piestany, 20.7.2011 18:31:00.9P wave Difference from real backazimuth 5°

  19. Earthquake N from Piestany, 20.7.2011 18:31:00.9S wave Difference from real backazimuth 7° Vp/Vs = 1.92

  20. Earthquake Dobrá Voda, 20.7.2011 23:52:14 48.61 N17.54 E Depth: 5kmML= -0.9Not detected by other seismic stations DOVA

  21. Earthquake Dobrá Voda, 20.7.2011 23:52:14P wave High apparent velocity 23.1 km/s

  22. Earthquake Nový Kostel, ML=1.6, Near epicenter Z NKCA

  23. Earthquake Nový Kostel, ML=3.3, Epic.Dist. 22 km Z LAZA

  24. Induced E.Provádia, ML=1.6, Near epicenter Z PROA

  25. Conclusions • Small-aperture seismic array DOVA started operation in May 2011 • Local events ML > -1 are recognized • Coherency for local earthquakes is weak comparing to other SSAs – DOVA is too large • Rotational components could be important – we suggest direct measurement using Rotaphone • We want to implement an automatic evaluation of DOVA data next year

  26. Generalized average of complex numbers p>0

  27. Generalized average of complex numbersxi = crosses, yp = dots

  28. Generalized average of signals 3

  29. Phase-weighted stack (Schimmel and Paulssen, 1997)

More Related