1. Larry D. Brown, Diego Quiros and Anastasija Cabolova Department of Earth and Atmospheric Sciences Cornell University, Ithaca, NY 14853 … and AIDA Virginia an AIDA Maine field teams

2. High resolution imaging of the sources More precise hypocenters More detailed V models (see below) Lower detection threshold Rupture histories by back projection High resolution imaging with the sources Refraction (tomography) for V p,s in 3D Reflection (cmp style) for structure Seismic interferometry, esp. body waves Objectives:

3. Field Experiments M 5.8 Mineral, Virginia August 23, 2011 M 4.0 Waterboro, Maine October 16, 2012

4. Z-component 3-component Non-AIDA Aftershocks Mw 5.8 Non-AIDA What is “dense”? Typical aftershock deployment: a few tens of instruments at  X ~ kms to 10’s of kms AIDA: 100’s of instruments At  x ~ 200 m Anti-alias:  x < min /2 ~ 100m ………………….

5. RT125 “Texan” 4.5 Hz vertical geophone 4.5 Hz 3C geophones (+ 3 Texans) Fast deployment (~5 min) Designed for controlled source (windowed recording) Can record continuously ~10 days @ 100 sps Uses standard D cell (2) Battery life ~ 3 days Procedures for changing battery while recording FlexArray Reftek Inc.

6. Deployment: AIDA VA Key limitations: Battery life Memory

7. Single event, single station EQ above, multiple stations Spectra 050 hz The Array Advantage 1 hour, multiple stations Chn 1 30 59 Dipping Events: Vehicles Flat Events: EQs Single Station Earthquake Obvious from Moveout Chn 1 30 59 Array

8. AIDA Detection Threshold Mw 1.8 USGS M w -0.7 Single Trace Chn 4 AmpdB 0-10040k-40k High Q, low noise environment

9. Aftershock Hypocenters using AIDA Locations for >200 aftershocks from Aug 27-Sept 9, 2011 Strike ~26° Dip ~52° SE Data misfits < 40ms, ~200m in given velocity model Davenport, Hole et al

10. Key Question: Reactivation or New Fault Aftershock Epicenters August 23, 2011 (Modified from C. Bailey) Aftershock zone geology: Piedmont Province crystalline thrust sheets Davenport, Hole et al

11. Crustal Reflections from Earthquake Sources PmP? P S  x = 200m 0 10 5 sec 6 km PxP X Broadside arrivals From another EQ Midpoints EQ Crustal Reflections from Earthquake Sources

12. Modeling reflections Model with horizontal Reflector at 6 km P direct S direct P reflected A1 A2 A1 A2

13. Reflection Geometry Aftershocks are in essence a Reverse VSP survey Surface Array Virtual Well  eqk

14. VSP CMP Imaging Schuster, 2009 Yu and Schuster, 2006

15. Reverse VSP gather + NMO (t) NWSENE Upper Crustal Reflection P S INLINEXLINE

16. CRP Processing of rVSP Conventional CMP vs VSP-CRP: Reflection point is function of source AND reflector depths After Hardage, 2002 Single trace as recorded at surface Trace mapped to x, z Multiple sources Multiple recorders Reflection energy Binned and stacked

17. Mineral VA in 3D rVSP + NMO (x,y,t) VA 1 eqk (single fold) Eqk Gather

18. VA Earthquake Reflection Image: 3D

19. Next CRP Stacking: Mapview: 3 Earthquakes

20. Ideal

21. Why not 5000 stations? True 3D/3C Example: Oyo GSR 1 month at 500 sps GPS onboard Cell QC, programmable > 4000 channels deployed in oil exploration

22. What is practical with existing technology ? 7.5 km  x = 200m 100 ch 1000 ch 4000 ch North Anna

23. Location Improvement: AIDA Maine (incl Weston Obs. Stations in blue and 10/23 epicenter as red icon) Quiros and Brown Cornell University 11/4/12

24. Wait, there’s more….

25. AIDA 3-C North Ana Nuclear Plant Fredericksburg Z-component 3-component

26. 3 component EW NSZ Attenuation Measurements

27. Surface Waves from Ambient Noise Cross-Correlated with Station 5 Band Pass 0.01-1.6 HzOffset Plot Velocity ~ 3500 ms -1 Processing: Band Pass-es 0.001-6 Hz. Station 5 is virtual souce. 5 days stacked. 4.5 Hz phones!

28. Virtual Surface Seismic Profile (seismic interferometry) Yu and Schuster, 2006 Source location is not needed!

29. What about P, S from “Ambient Noise”? Virtual Source EQ distribution non-isotropic Cross-Correlation with Station 13 (7 days) Resembles EQ time-shifted to the surface Virtual Shot Gather

30. Applications: Aftershocks 3D seismic structure Volcano seismicity 3D magmatic structure Induced microseismicity 3D P and S refraction&reflection Noisy environment? Detection threshold? Adv/Disadv vs borehole? 4D

31. Needs for Crustal Imaging Large numbers (1000’s) Long lasting (months) Easily deployable Self locating 3C Sensors: 0.1-100hz

32. Conclusions Rapid, high density deployments are imminently feasible High precision  seismic locations, source properties High resolution imaging of local structure using Earthquakes as deterministic sources Tomographic P,S imaging (refraction) 3D reflection imaging S and well as P? Earthquakes as stochastic sources Seismic Interferometry Event location, time not required! Possibility of detailed 4D (e.g. time lapse) source region monitoring

33. Special Thanks to Geophysics Division: RAPID Grant Bruce Beaudoin, Patrick Bastien, Noel Barstow from PASSCAL Student volunteers from James Madison University and Washington and Lee University Vista Software

34. Areal Array Dx ~ 5 km Dense Linear Array Dx = 200m ME Aftershock 10/27/12 Quiros and Brown Cornell University 11/4/12 Zoom

35. Location Improvement AIDA Maine