1. Imaging with Non-Aliased Seismic Wavefields Large N (and not just sensors) John Hole, IRIS Active Source Workshop, 2014 John Hole Virginia Tech SPATIAL ALIASING resolution WAVEFIELDS NOT JUST WAVEFORMS

2. John Hole, IRIS Active Source Workshop, 2014 Non-Aliased Seismic Wavefields seismic reflection uses non-aliased wavefields since the 1950’s continuity of arrivals => unwrap statics problem, cycle skips data redundancy improves S/N => “fold” enables wavefield imaging (stacking, migration, etc.) need for both shots and receivers to be non-aliased rest of this presentation: - imaging examples using non-traditional wavefield imaging - description of IRIS’s Large N initiative

3. John Hole, IRIS Active Source Workshop, 2014 structure of the San Andreas fault zone context for $20M drill hole 1999: 4.9 km straight line 10 m shots, 1 kg 5 m stations 2003: 46 km straight line 0.5 km shots, 25 kg dense, but aliased 50 m stations (3-component telemetered MEMS) not funded: 3-D multichannal + VSP proposed ($2.7M) rejected due to cost SAFOD

4. John Hole, IRIS Active Source Workshop, 2014 SAFOD: Waveform Inversion travel time tomography waveform inversion Bleibinhaus et al., 2007

5. John Hole, IRIS Active Source Workshop, 2014 requirements: - non-aliased stations - not/weakly aliased at shots - excellent starting model - low frequencies => dense spacing + long offsets => Large N SAFOD: Waveform Inversion Bleibinhaus et al., 2007

6. John Hole, IRIS Active Source Workshop, 2014 SAFOD: Steep-Dip Migration Bleibinhaus et al., 2007 Hole et al., 2001 requirements: - non-aliased stations - not/weakly aliased at shots - wide-angle offsets and times - excellent velocity model => dense spacing + long offsets => Large N Hole et al., 1996

7. John Hole, IRIS Active Source Workshop, 2014 lithology! SAF SAFOD: Three Component Vp & Vs Ryberg et al., 2012 requirements: - S waves, ideally from 3-component stations

8. John Hole, IRIS Active Source Workshop, 2014 SAFOD: Low-Fold Energy Stack Bleibinhaus et al., 2007 dense receivers migrated shot gathers

9. John Hole, IRIS Active Source Workshop, 2014 SAFOD: Low-Fold Energy Stack dense receivers migrated shot gathers much worse than multichannel aliased shots cannot stack waveforms => low-fold energy stack Bleibinhaus et al., 2007

10. John Hole, IRIS Active Source Workshop, 2014 several 30-50 km lines 2-4 km shots aliased 100 m stations not sufficient for multi-channel reflection => low-fold energy stack in progress maybe(?) sufficient for waveform inversion, but only where surface geology is very uniform => in progress perhaps(??) sufficient for steep-dip pre-stack migration => only line-segment migration to date SSIP

11. Batholiths 2009 SSIP 2011 IDOR 2012 John Hole, IRIS Active Source Workshop, 2014 Continuous Recording continuous recording on Texans limited by power, RAM, to ~75 hours at 4 ms allows flexibility to shoot when ready records ambient noise, including earthquakes AIDA 2011

12. Shot Gather Receiver Gather Surface wave P-wave John Hole, IRIS Active Source Workshop, 2014 SSIP: Ambient Noise noise sources: - geothermal plants (surface and pumping) - 2 highways, 1 railroad - micro-earthquakes (tectonic and induced) - agricultural operations - waves in Salton Sea Sabey et al., 2013 excellent information about shallow subsurface but does not replace active sources for deeper imaging 10-50 Hz, to 4 km distance reflections in progress; <1 km depth 0.4-8 Hz (on 4.5 Hz phones) to 600 m depth surface waves body waves

13. P PcP 0.5-5.0 Hz 60 s PmS 29-station broadband array - vertical IDOR: M7.7 Eastern Russia Earthquake Stanciu et al., 2013 John Hole, IRIS Active Source Workshop, 2014

14. P PcP 0.1-1.0 Hz on 4.5 Hz geophones! 60 s PmS 2555-station Texan array - vertical correlation => signal Davenport et al., 2013 John Hole, IRIS Active Source Workshop, 2014 IDOR: M7.7 Eastern Russia Earthquake

15. AIDA Virginia Davenport et al., in press 148 stations 200-400 m spacing 12x12 km array of lines several thousand aftershocks John Hole, IRIS Active Source Workshop, 2014

16. AIDA Virginia: Aftershocks Davenport et al., in press magnitude 2.0 John Hole, IRIS Active Source Workshop, 2014

17. 1 km 0 s 0.10 s 0.05 s 0 s 0.05 s 0.10 s 1 km Wang et al., 2013 AIDA Virginia: Aftershocks magnitude 3.7 source back-projection (3-D reverse time migration) smallest point-source migrated: M(-2) John Hole, IRIS Active Source Workshop, 2014

18. 1 km 0 s 0.10 s 0.05 s 0 s 0.05 s 0.10 s 1 km AIDA Virginia: Aftershocks Wang et al., 2013 magnitude 3.7 source back-projection (3-D reverse time migration) smallest point-source migrated: M(-2) smallest slip propagation resolved: M2.5 John Hole, IRIS Active Source Workshop, 2014

19. Current Status of (Onshore) Academic Community seismographs: 2-D not aliased (thanks to the Texans) 3-D 10’s of stations x 10’s of stations => usually aliased 3-C a few hundred stations => usually aliased sources: => horribly aliased

20. John Hole, IRIS Active Source Workshop, 2014 IRIS’s current instrumentation and field procedures are 20+ years old limits the science that we can do past decades have seen rapid improvements in technology improved instruments are possible improving technology enables new science IRIS’s Large N Initiative

21. John Hole, IRIS Active Source Workshop, 2014 IRIS’s Large N Initiative “Large N” = arrays recording non-aliased wavefields instruments: - much less expensive - much simpler to deploy & retrieve - much simpler to retrieve useful data (dirt to desktop) - high quality signals - broadest possible range of applications, from 1 m to 10,000 km transform how we acquire data to enable wavefield imaging methods SPATIAL ALIASING resolution WAVEFIELDS NOT JUST WAVEFORMS

22. broadband ~$35k >100 kg 3-6-hour deployment solar power long period high sensitivity 3-component large memory GPS Texan ~$4k <2 kg 3-minute deployment 2 D cells power high frequency modest sensitivity 1-component small memory internal clock combine the best of both probably some compromises efficiencycapacity John Hole, IRIS Active Source Workshop, 2014 IRIS’s Large N Initiative

23. John Hole, IRIS Active Source Workshop, 2014 in IRIS’s FY2014-2018 NSF Cooperative Agreement: continue providing existing instrument services and development of Large N IRIS’s Large N Initiative

24. John Hole, IRIS Active Source Workshop, 2014 Large N Working Group (chair: John Hole) task: compile… What new science could be enabled by Large N? not the focus: technical instrument needs series of online workshops February-April 2014 single seismic community per workshop controlled-source: February, hosted by Katie Keranen marine, OBSIP: use recent workshop (Van Avendonk) glossy white paper report: Scientific Potential => NSF, DOE, DOD, USGS, Industry, … IRIS’s Large N Initiative

25. John Hole, IRIS Active Source Workshop, 2014 Sources sources are not in IRIS’s Large N… budget is a major issue non-aliased shots are too expensive during NSF review process  the last onshore deep reflection survey was CD-ROM (1999)  marine seismic reflection is currently at risk possible solution: a facility that removes the source cost from the PI budget enables science that a PI-driven proposal cannot perform a community facility, not just a community project a virtual facility via standing contracts, rather than instrumentation