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Aftershock Imaging with Dense Arrays (AIDA):

Aftershock Imaging with Dense Arrays (AIDA):. 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

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Aftershock Imaging with Dense Arrays (AIDA):

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  1. Aftershock Imaging with Dense Arrays (AIDA): • 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 Vp,s in 3D • Reflection (cmp style) for structure • Seismic interferometry , esp. body waves Objectives:

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

  3. AIDA Recording Hardware • 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 RT125 “Texan” 4.5 Hz vertical geophone 4.5 Hz 3C geophones (+ 3 Texans) Reftek Inc. FlexArray

  4. 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

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

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

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

  8. Reflection Geometry Virtual Well Surface Array meqk Aftershocks are in essence a Reverse VSP survey

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

  10. 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 Reflection energy Binned and stacked Trace mapped to x, z Multiple sources Multiple recorders

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

  12. VA Earthquake Reflection Image: 3D

  13. Next CRP Stacking: Mapview: 3 Earthquakes

  14. Ideal

  15. 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

  16. What is practical with existing technology? Dx = 200m North Anna 100 ch 1000 ch 4000 ch 7.5 km

  17. 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

  18. Wait, there’s more….

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

  20. Attenuation Measurements 3 component EW NS Z

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

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

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

  24. 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

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

  26. ME Aftershock10/27/12 Areal Array Dx ~ 5 km Dense Linear Array Dx = 200m Zoom Quiros and Brown Cornell University 11/4/12

  27. Location Improvement AIDA Maine

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