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Double-difference location method: principles and application to microseimic data

Double-difference location method: principles and application to microseimic data . Fateh Bouchaala. Algorithm (F. Waldhauser & W L. Ellsworth). Standard approach. : Travel time from hypocenter i to seismic station k. : Spatial coordinates of hypocenter i. : Origin time of event.

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Double-difference location method: principles and application to microseimic data

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  1. Double-difference location method: principles andapplication to microseimic data Fateh Bouchaala AIM project, Prague

  2. Algorithm (F. Waldhauser & W L. Ellsworth) Standard approach : Travel time from hypocenter i to seismic station k : Spatial coordinates of hypocenter i. : Origin time of event. : Residual time : Perturbation AIM project, Prague

  3. Algorithm (F. Waldhauser & W L. Ellsworth) Doubledifference G : Matrix containing the partial derivaties; size Mx4N (M number of pairs; N number of hypocenters) m : Vector containing the changes in hypocentral parameters, size, 4xN. d : Vector containing double difference , size M. AIM project, Prague

  4. Algorithm (F. Waldhauser & W L. Ellsworth) Station k Station l y x depth event j event i AIM project, Prague AIM Project

  5. Advantages of the method • The travel time differences can be related with high accuracy to the offsets between hypocenters • It allows the use of difference time computed from cross correlation • The common mode errors can be neglected, as those related to the receiver-side structure • Can be used for high number of events • Free software (hypoDD). Application examples of the method • Northern Hayward Fault, North California earthquakes, 1984-1998 (F. • Waldhauser & W L. Ellsworth. 2000). • Southern California earthquakes, 1984-2002 (E.Hauksson and P.Shearer. 2005) AIM project, Prague

  6. Method application (West Bohemia) 50.4°- • West Bohemia Seismic Network (WEBNET) : • 13 permanent and 10 mobile stations • Swarm 2008 • Magnitude < 3.8 • Dense distribution 50°- http://www.ig.cas.cz 12° 12.4° 12.8° AIM project, Prague

  7. دعاء القلق

  8. HYPODD software (F. Waldhauser & W L. Ellsworth) Initial location + Structure Model N Pair eventsselection Some conditions Pair events iscancelled Y Pair eventsis saved Initial location + P or/and S wave + Catalog or/and correlated data Events relocation AIM project, Prague

  9. Computation Time M (number of events) : 478 Number of station : 23 N (number of pair-events) : more than 500000 pairs Data RAM : 2.0 GB Computer characteristics Processor : intel(R) Corel(TM)2.40 GHZ System : Linux Time consuming : less than 1 hour AIM project, Prague

  10. Results (478 events are relocated) N Cross correlation data, P and S waves are used. E W S AIM project, Prague

  11. Results (478 events are relocated) Cross correlation data, P and S waves are used. East AIM project, Prague

  12. Results (478 events are relocated) Cross correlation data, P and S waves are used. East AIM project, Prague

  13. Results (478 events are relocated) Cross correlation data, P and S waves are used. East AIM project, Prague

  14. Results (478 events are relocated) Cross correlation data, P and S waves are used. East AIM project, Prague

  15. Results (478 events are relocated) N Comparison relocated and initial location : E W S AIM project, Prague

  16. Results (478 events are relocated) Comparison relocated and initial location : East AIM project, Prague

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  29. Conclusion • DD method improves the event location accuracy • The use of this method has resulted in a reduced dispersion of hypocenters, which leads to a better identification of fault segments • Fault plane activated in West Bohemia in 2008 is complex with several segments • The fault complexity is proved by focal mechanisms AIM project, Prague

  30. Perspective • To relocate the West Bohemia earthquakes recorded in 2009 to study the deeper part of the fault • To relocate microseismic data in other regions (e.g., the Dobra Voda area) • To relocate data recorded at laboratory experiments provided by project partners 29.09.2011 AIM project, Prague 30

  31. Acknowledgements I thank Josef Horálek, Alena Boušková and other colleagues from the WEBNET group for providing me with the data from the 2008 swarm activity and for kind help with their preprocessing. 29.09.2011 AIM project, Prague 31

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