Recent Studies in Earthquakes Slow and Fast Slip Events: How Could We Study Them??

1. Recent Studies in Earthquakes Slow and Fast Slip Events: How Could We Study Them?? • Kevin M. Brown • kmbrown@ucsd.edu: Scripps Institution of • Oceanography, University of California, San Diego, • La Jolla, CA 92093-0244, United States

2. Experimental Investigation of a Transition Between Stick-slip and Creep as Function of Temperature, Slip-Rate, and Normal stress A possible origin of slow slip events Erica Mitchell, Kevin Brown, Yuri Fialko Scripps Institution of Oceanography, UCSD AGU - T16

4. Effective Normal stress Transitions to Unstable Behavior in 3D Phase Space Complex Transition Zones Temp Fast a s Strain rate a Slow a - aseismic s - seismic

5. Novaculite T=200°C Normal Stress=4MPa Forcing Velocity=10-4mm/s T=25°C Normal Stress=1MPa Forcing Velocity=10-2mm/s Slip Time= < 0.1sStress Drop= 0.664MPaSlip Velocity= >>1mm/s Slip Time=4.8s Stress Drop=.01MPa Slip Velocity=2.5x10-4mm/s 1) 2) Increasing Instability T=200°C Normal Stress=4MPa Forcing Velocity=10-5mm/s Slip Time=90s Stress Drop=0.043MPa Slip Velocity=5.78x10-5mm/s 4) 3) T=500°C Normal Stress=8MPa Forcing Velocity= 10-3, 10-2, 3x10-2mm/s

6. Onset of Melting

7. Change in physics with slip velocity Peak Thermal Fabric/ localization Friction Coefficient Residual

8. Do Field Studies And Get Lucky!

10. We already know the Nicoya area of Costa Rica is dangerous (Mw 7.8, potentially tsunamogenic) and interesting What is partial plate coupling?? Geodetically coupled region does not appear to be related to smectite to illite transition (too cold) Newman

11. OBS, flowmeter box

12. Early micro-observatories ACDP Current meter Remotechambers Marine Hydrologic Instrumentation on a Cold Seep

13. Nicoya

14. Brown, Deshone Dorman, Schwartz, Tryon Correlations Between Flow and Noise • Correlation between noise and flow anomalies is clear. • Sites show flow anomalies of differing signs.

15. “Seismic Noise” Manifestations

16. Comparison of wind and noise A) Regional RMS noise average of 8 instruments B) Significant wave height off Costa Rica from meteorology using Tolman's WaveWatchIII program C) RMS records, and regional average noise. Note that site 5 stands out

17. See Dorman Poster Tremor or Many Micro Earthquakes?

18. Spectrogram of event 3 at site 3Record length is 12 hours See Le Roy Dormans poster

19. Spectrogram of event 3 at site 5Record length is 12 hours See Le Roy Dormans poster- From duel frequency studies-noise is similar too but not exactly like Julian 1994 tremor

20. Hydrologic Manifestations

21. The finite element model: Abacusa fully coupled model (LaBonte,Brown, Fialko) Costa Rica subduction zone geometry oceanic plate continental plate • Numerical calculation of: • displacement • pore pressure • fluid flow • (tilt and volumetric strain • also possible)

22. Flow patterns differ between Near/Far Field Earthquake - Depth > Rupture length The finite element model: Abacusa fully coupled model (LaBonte, Brown, Fialko) Near surface flow/pore pressure signals are a combination of poro-elastic effects and surface buckling/flexure effects

23. Updip Propagating Slow Slip c c c =1 =0.5 =0.05 flow rate time OUT FLOW AT SURFACE

24. Downdip propagating slow slip c flow rate c c =0.5 =0.05 =1 time

25. model Flow rate (mm/day) Days since event initiation Down dip propagation, = 0.4 Duration of slow slip event = 22days Site 2 is 6.5km distant from trench Maximum extent= 0.5km-15km Max. prop. velocity= 0.7km/day Min. dislocation distance= ~30cm

26. Updip propagation Downdip propagation c =0.2 flow rate c =0.5 time c =1 flow rate time

27. One Strategy for a Subduction Zone Earthquake Observatory Buoys- Marine Geodetics 2) Boreholes 3) Cables

28. 8 Locked to the trench 8 Locked to the trench 6 4 2 0 Stress episodically released near the toe Note on land geodetic measurements are not sensitive to offshore locking patterns only the down dip limit! Continuous marine geodetic measurements can determine where the up dip limit lies and how it stresses are released episodically

29. SeisCORK Concept • for time lapse VSPs and offset VSPs • - for monitoring micro-earthquake activity

30. DYNASEISE: Geodynamic and SeisCORK Observatories in the Central America Subduction System, Costa Rica GEOCE Buoys Kevin Brown, Ralph Stephen, Andrew Newman, Tom Pettigrew, Bob Petit, Kirk McIntosh, Sue Bilek, Nathan Bangs, LeRoy Dorman, Glen Spinelli, Susan Schwartz, Pete Lafemina

31. CRSZ-1

32. Hilton Fischer, Brown Gradient He Ra numbers Wedge mantle boundary

33. GEOCE BUOY

35. An ORION-Type Observatory s Multiple Components: Horizontal marine GPS (cm) Verticalseabed height changes (<1cm) oceanographic variability (internal density and dynamic height changes Absolute sea height Buoy GPS Communications (acoustic and radio/satellite)

38. GEOCE system 1) XYZ seabed displacement 2) Corrected for oceanic noise 3) Initial system engineering test is ongoing off SIO 4) Highest data retrieval rates will be obtained by line of sight wireless modem. 5) Really useful for slow slip and aseismic creep events

39. Conclusion • A very wide variety of methods and techniques are required to make progress!