Understanding Dynamic Triggers in Seismic Activity

1. ‘Triggering’ = a perturbation in the loading deformation that leads to a change in the probability of failure. How do we know it happens?

2. ‘Triggering’ = a perturbation in the loading deformation that leads to a change in the probability of failure. • How do we know it happens? • Measure or infer a loading perturbation, & observe a change in • seismicity rate (fault population or single fault recurrence), • possibly its spatial variation too.

3. The ‘Reference’ State Central California Ambient Seismicity

4. The Perturbation Coyote Lake Mainshock & Ambient Seismicity

5. The Perturbation & Response Coyote Lake Mainshock & Aftershocks

6. Dynamic loads: • Seismic waves (oscillatory, transient)

7. Dynamic loads: • Seismic waves (oscillatory, transient) • Aseismic slip (not oscillatory, may be permanent)

8. Dynamic loads: • Seismic waves (oscillatory, transient) • Aseismic slip (not oscillatory, permanent) • Solid earth tides and ocean loading (oscillatory, ongoing)

9. Dynamic loads: • Seismic waves (oscillatory, transient) • Aseismic slip (not oscillatory, permanent) • Tides (oscillatory, ongoing) • Surface/shallow: snow and ice, reservoir filling/draining, mining, ground water, fluid injection or withdrawal (localized) • Magma movement (temperature, pressure, and chemical changes too)

10. What’s unique about dynamic loads?

11. What’s unique about dynamic loads? They’re transient!

12. failure threshold shear stress time Static Load Change Dt

13. Static Load Change Dt failure threshold Dt shear stress time

14. failure threshold shear stress time Dynamic Triggering

15. Dynamic Triggering failure threshold Dt shear stress time

16. What’s unique about dynamic loads? They’re transient; the failure conditions must change! failure threshold Dt shear stress time

17. What’s unique about dynamic loads? They’re transient; the failure conditions must change! They’re oscillatory, but they only enhance failure probability (ASSUMPTION); no stress shadows.

18. What’s unique about dynamic loads? They’re transient; the failure conditions must change! They only enhance failure probability (ASSUMPTION); no stress shadows. Slower distance decay than static stress changes.

19. Dynamic Triggering Observations (by load type) • Seismic waves (transient, oscillatory) • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent • Quasi-seismic responses • Laboratory • Aseismic slip (slow, permanent) • Tides (oscillatory, ongoing) • Surface/Shallow: snow and ice, reservoir filling/draining, mining, ground water, fluid injection or withdrawal (localized)

20. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Seismicity rate increases following large earthquakes.

21. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Seismicity rate increases following large earthquakes.

22. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Seismicity rate increases following large earthquakes.

23. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Seismicity rate increases following large earthquakes. • Missing? rate increases.

24. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Correlation of spatial rate increase with directivity.

25. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Correlation of spatial rate increase with directivity. • Correlation of (no) rate change with co-located seismic & aseismic events. Pollitz & Johnston, 2007

26. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Correlation of spatial rate increase with directivity. • Correlation of (no) rate change with co-located seismic & aseismic events. Pollitz & Johnston, 2007

27. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Correlation of spatial rate increase with directivity. • Correlation of (no) rate change with co-located seismic & aseismic events. • Early excess of aftershocks. • Rate increases in stress shadows. Chi-Chi earthquake shadows start with 3-month rate increases. Ma et al., 2005 1998 1999 2000 2001 2002 1998 1999 2000 2001 2002

28. “Observed seismicity rate decreases in the Santa Monica Bay and along parts of the San Andreas fault are correlated with the calculated stress decrease.” Stein, 1999

29. “Observed seismicity rate decreases in the Santa Monica Bay and along parts of the San Andreas fault are correlated with the calculated stress decrease.” Stein, 1999 Time history of seismicity from Santa Monica Bay (Marsan, 2003).

30. “The [Stein, 1999] interpretation is made difficult by the fact that the transient activity modulation by the 1989 M5 Malibu earthquake was still ongoing….the quiescence observed after 1994 can be tracked back several months before Northridge, the latter main shock actually triggering seismicity in the region at the very short (i.e. days) timescale. Marsan, 2003

31. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Measured Linear Aftershock Densities Felzer & Brodsky, 2006

32. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Modeled Linear Aftershock Densities g constant! number of aftershocks at distance r number of potential nucleation sites per unit distance probability of nucleation

33. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view triggering fault D ‘Linear density’ = number of aftershocks within a volume defined by surface S everywhere at distance r and width Dr

34. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Modeled Linear Aftershock Densities

35. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Modeled Linear Aftershock Densities

36. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Modeled Linear Aftershock Densities

37. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Are dynamic deformations consistent with these probabilities?

38. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Are dynamic deformations consistent with these probabilities? Peak Velocities vs r, M5.5-7.0

39. Dynamic Triggering Observations (by loading type) Seismic waves Remote (many source dimensions) Near-field (few source dimensions) Distance-independent view Are dynamic deformations consistent with these probabilities? perhaps! Peak Velocities vs r, M5.5-7.0 Peak Velocities vs r/D, M5.5-7.0

40. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • ‘Low-frequency’ events Sumatra surface waves in Japan High-passed Sumatra surface waves in Japan Correlation with Rayleigh waves - Dilatation & Fluids Miyazawa & Mori, 2006

41. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • ‘Low-frequency’ events Sumatra surface waves in Japan Denali surface waves in Japan, Correlation with Love waves - Shear Load! High-passed Sumatra surface waves in Japan Correlation with Rayleigh waves - Dilatation & Fluids Miyazawa & Mori, 2006 Rubinstein et al., 2007

42. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • ‘Low-frequency’ events • Creep and tilt Response to Hector Mine waves on Imperial Fault (260 km) H H Glowacka et al., 2002

43. Dynamic Triggering Observations (by loading type) • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • Laboratory Granular surface quasi-static experiments. “Our results predict that a transient dynamic normal load during creep can strengthen a fault…gouge particles become compacted into a lower energy configuration.” Richardson and Marone, 1999

44. delayed failure • Dynamic Triggering Observations • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • Laboratory delayed failure Granite surface stick-slip experiments. Sobolev et al., 1996

45. delayed failure • Dynamic Triggering Observations • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • Laboratory delayed failure Vibration Clock-advances Failure Granite surface, shear vibration, stick-slip experiments. Sobolev et al., 1996

46. Dynamic Triggering Observations • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • Laboratory Granular surface, acoustic vibration, stick-slip experiments.

47. Dynamic Triggering Observations • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • Laboratory triggered ‘new’ seismic events triggered ‘new’ seismic events clock-delayed failure acoustic transient acoustic transient Granular surface, acoustic vibration, stick-slip experiments.

48. Dynamic Triggering Observations • Seismic waves • Remote (many source dimensions) • Near-field (few source dimensions) • Distance-independent view • Quasi-seismic responses • Laboratory triggered ‘new’ seismic events memory clock-delayed failure acoustic transient acoustic transient Granular surface, acoustic vibration, stick-slip experiments.

49. Dynamic Triggering Observations (by loading type) • Seismic waves • Aseismic slip • Earthquakes Hawaii Slow Slip & Earthquakes Number of earthquakes & displacement

50. Dynamic Triggering Observations (by loading type) • Seismic waves • Aseismic slip • Earthquakes • Tremor Cascadia Slow Slip & Tremor Geodetic Displacement (mm east) Tremor Activity (hrs in 10 days) Dragert et al., 2002