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

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

6. Onset of Melting

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

8. Do Field Studies And Get Lucky!

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

11. OBS, flowmeter box

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

13. Nicoya

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

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. Tremor or Many Micro Earthquakes? See Dorman Poster

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

19. Spectrogram of event 3 at site 5 Record 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: Abacus a fully coupled model (LaBonte,Brown, Fialko) Numerical calculation of: displacement pore pressure fluid flow (tilt and volumetric strain also possible) Costa Rica subduction zone geometry oceanic plate continental plate

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

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

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

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

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

27. One Strategy for a Subduction Zone Earthquake Observatory 1)Buoys- Marine Geodetics 2) Boreholes 3) Cables

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

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 Kevin Brown, Ralph Stephen, Andrew Newman, Tom Pettigrew, Bob Petit, Kirk McIntosh, Sue Bilek, Nathan Bangs, LeRoy Dorman, Glen Spinelli, Susan Schwartz, Pete Lafemina GEOCE Buoys

31. CRSZ-1

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

33. GEOCE BUOY

35. An ORION-Type Observatory s Multiple Components: 1)Horizontal marine GPS (cm) 2)Verticalseabed height changes (<1cm) oceanographic variability (internal density and dynamic height changes 4)Absolute sea height Buoy GPS 5)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!