1. Repeating Earthquakes Olivier Lengliné - IPGS Strasbourg Cargese school

2. Please interrupt Questions / remarks

3. 1 – Review of Repeating earthquake observations & interpretations 2 – Two examples of application

4. Observations - Waveforms Nadeau & Johnson, 1998

5. Parkfield, California – Mw6.0 USGS Bakun et al., 2005 De Bilt, The Netherlands

6. Uchida et al., 2012 Time (s) Off Kamaishi, Japan – M4.9

7. Chen et al., 2008 Chihshang fault, Taiwan

8. Time (s) 9 events 13 events 19 events Soultz-Sous-Forêts geothermal reservoir, France BRGM

9. San-Andreas Fault Schaff & Beroza, 1998 Rubinstein et al., 2012

10. u(t) = Source * Path * Station

12. Station is the same Change in medium property, [e.g Poupinet et al., 1984] Change in source properties, [e.g. Lengliné & Got, 2011]

13. Poupinet et al., 1984 Lengliné and Got, 2011 Directivity Velocity variations

14. u(t) = Source * Path * Station Station the same Change in medium property, [e.g Poupinet et al., 1984] Change in source properties, [e.g. Lengliné & Got, 2011] ! Homogeneous medium  waveform similarity

15. Observations - Locations Waldhauser et al., 2004

16. Murray & Langbein, 2006 Parkfield

17. Off Kamaishi Okada et al., 2002 Relative moment released normalized by each maximum value Moment release distribution

18. Earthquake relative relocation  Uncertainties P-wave picks  Uncertainties of the velocity model

19. Earthquake relative relocation  Uncertainties P-wave picks  Uncertainties of the velocity model  More precise data: time delays estimated from cross-correlation  Ray geometry – rotation  Do not correct absolute position

20. Earthquake relative relocation  Uncertainties P-wave picks  Uncertainties of the velocity model  More precise data: time delays estimated from cross-correlation  Ray geometry – rotation  Do not correct absolute position From cross-correlation  centroid location Got et al., 1994 Waldhauser & Ellsworth, 2000

21. Earthquake relative relocation  Uncertainties P-wave picks  Uncertainties of the velocity model  More precise data: time delays estimated from cross-correlation  Ray geometry – rotation  Do not correct absolute position From cross-correlation  centroid location Got et al., 1994 Waldhauser & Ellsworth, 2000 See Tutorial this afternoon for Methods

22. Lengliné & Marsan, 2008 Size = Assumed stress drop + circular crack + moment – magnitude relation

23. Bourouis & Bernard, 2007 Chen et al., 2008 Soultz-sous-Forêts Taiwan Radius estimated from corner frequency

24. Murray & Langbein, 2006 Rau et al., 2007 Clusters of co-located, similar waveforms earthquakes, appears at the transition between fully locked and fully creeping areas

25. Waldhauser & Schaff, 2008 Example from Northern-California Parkfield Is it related to fault slip velocity ?

26. Rubin et al., 1999 San Andreas Fault Streaks of microearthquakes – along slip direction Rheological / frictional / geological / geometrical transition ?

27. Observations - Timing

28. YearNumber 18571 18812 19013 19224 19345 19666 20047 μ Δt = 24.5 yr σ Δt = 9.5 yr COV = 0.37 Time (years) Earthquake number Parkfield

29. Repeaters off Kamaishi Repeating interval = 5.35 +/- 0.5 yrs Time (years)

30. Waldhauser et al., 2004 Distance along strike (km) Year San-Andreas fault at Parkfield

31. Waldhauser et al., 2004 Distance along strike (km) Year Periodic repeating ruptures

32. Rubinstein et al., 2012 Quasi-periodic behavior of the slip activity

33. Aseismic slip No interacting asperity The simplest model A locked seismic patch embedded in a fully creeping zone

34. Slip on the creeping part Slip on the seismic asperity Time Slip

35.  Aseismic slip on the fault = seismic slip Time Slip d seis

36.  Aseismic slip on the fault = seismic slip  Elastic solution for a circular crack

37.  Aseismic slip on the fault = seismic slip  Elastic solution for a circular crack

38.  Aseismic slip on the fault = seismic slip  Elastic solution for a circular crack  Constant stress drop

39. Chen et al., 2007

40. 1st Hypothesis The constant stress drop hypothesis is not correct Empirical fit to the data then suggests in order to have T r ~ M 0 1/6 Implies that the stress-drop is higher for small events. Stress levels reach 2 GPa for the smallest events (more than 10 times laboratory strength) This result is at odds with estimates based on seismic spectra Relation not consistent with established scaling relations for large earthquakes.

41. Imanishi & Ellsworth, 2006

42. Chen & Lapusta, 2009

43. But not the estimated plate velocity – streaks close to locked section  reduced velocity ?

44. Slip on the creeping part Slip on the seismic asperity Time Slip Seismic slip

45. Uchida, 2014 Off Kamaishi repeating sequence following Tohoku, 2011, Mw9 earthquake

46. Lengliné & Marsan 2008 Schaff & Beroza, 1998

47. Following Parkfield, 2004, Mw6 event

48. Response of a velocity strengthening area to a stress-step Marone, 1991 The Omori like decay of RES is well rendered by the slip evolution of the creeping area following a stress step

49. Nadeau & McEvilly, 1999

51. Bourouis & Bernard, 2007

52. Bouchon et al., 2011

53. Kato & Nakagawa, 2014 Kato et al., 2012

54. Repeating earthquake are local (sparse) creep-meter at depth Difficult to quantify if the seismic slip reflects the surrounding aseismic loading

55. Time after 01/01/1984 (years) Number of earthquakes Complications to the idealized picture Repeating sequence of small micro-earthquakes at Parkfield

56. Time after 01/01/1984 (years) Number of earthquakes Complications to the idealized picture Repeating sequence of small micro-earthquakes at Parkfield

57. Interactions from nearby small events Chen et al., 2013 More isolated events = more periodic

58. Vidale et al., 1994 How can strength of the interface build up so quickly between 2 events ? Healing of the interface

59. What is an asperity ? (geometrical/frictional/geological …) What is the lifetime of an asperity ? In which case do we observe periodicity ? (density of asperity) Are repeating LFE earthquakes obeying a similar mechanism ? Questions

60. 2 examples of use of repeating earthquake sequences -Earthquake detection and time activity (with P. Ampuero) -Variation of source properties (with L. Lamourette, L. Vivin, N. Cuenot, J. Schmittbuhl)

61. Parkfield

63. Landweber deconvolution Example for one pair at one station

64. Landweber deconvolution All pairs at all stations

65. Sparse deconvolution 54 new detected events in the first 20s following a repeating earthquakes

66. Stack aftershock sequence Typical rupture duration

68. Wang et al., 2014

69. Omori’s law extended almost up to the rupture duration Implies a very low c-value and thus a very large stress changes in the R&S Dieterich framework Seismicity rate Time (t/t a ) No flatenning of the earthquake rate at early times Is this particular to the repeating earthquakes ?

70. Station surface sites 150 Hz sampling frequency 2010 11 months long circulation test 411 earthquakes recorded Largest magnitude event M2.3

71. 4 groups of similar events Relocation suggest a similar location Each group have at least one event larger than 1.4 4/6 of the largest events of the circulation are included in these groups

72. SVD analysis (Rubinstein & Ellsworth, 2010 ) Up to a factor x 300 of moment ratio

73. SVD analysis (Rubinstein & Ellsworth, 2010 ) Up to a factor x 300 of moment ratio

74. For the largest event of each group

75. Corner frequency of the largest event of each group f c ~ [10-20] Hz

76. Wiener filter (equivalent to spectral ratio) Same rupture area

78. The difference of seismic moment reflects a difference of seismic slip/ stress drop Increase of pore pressure lowers the normal stress on the fault plane 2 effects: Shear failure promoted (reach the Coulomb enveloppe) Stabilizes the slip Several instances of aseismic movements have been suggested in the Soultz reservoir We are observing a transition from unstable to stable slip on the interface Bourouis & Bernard, 2007

79. Thank you