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

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

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

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

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

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

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

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

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

John Hole, IRIS Active Source Workshop, 2014 several 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

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

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 Hz, to 4 km distance reflections in progress; <1 km depth Hz (on 4.5 Hz phones) to 600 m depth surface waves body waves

P PcP 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

P PcP 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

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

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

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

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

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

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

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

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

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

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

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