imaging with non-aliased seismic wavefields large n (and not just sensors) john hole, iris active...

Imaging with Non-Aliased Seismic WavefieldsLarge N (and not just sensors)

John Hole, IRIS Active Source Workshop, 2014

John HoleVirginia Tech

SPATIALALIASING

resolutionresolutionresolution

WAVEFIELDSNOT JUST WAVEFORMS


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


structure of the San Andreas fault zonecontext for $20M drill hole

1999:4.9 km straight line10 m shots, 1 kg5 m stations

2003: 46 km straight line0.5 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


SAFOD: Waveform Inversion

travel time tomography

waveform inversion

Bleibinhaus et al., 2007


requirements:- non-aliased stations- not/weakly aliased at shots- excellent starting model- low frequencies => dense spacing + long offsets => Large N

SAFOD: Waveform Inversion



SAFOD: Steep-Dip Migration


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


lithology!

SAF

SAF

SAFOD: Three Component Vp & Vs

Ryberg et al., 2012

requirements:- S waves, ideally from 3-component stations


SAFOD: Low-Fold Energy Stack


dense receiversmigrated shot gathers


SAFOD: Low-Fold Energy Stack

dense receiversmigrated shot gathers

much worse than multichannel

aliased shotscannot stack waveforms=> low-fold energy stack



several 30-50 km lines 2-4 km shots aliased100 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


Continuous Recording

continuous recording on Texans limited by power, RAM, to ~75 hours at 4 msallows flexibility to shoot when readyrecords ambient noise, including earthquakes

AIDA 2011

Shot Gather Receiver Gather

Surface waveSurface wave

P-waveP-wave


SSIP: Ambient Noisenoise 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 distancereflections in progress; <1 km depth

0.4-8 Hz (on 4.5 Hz phones) to 600 m depth

surface waves

body waves

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


P

PcP

0.1-1.0 Hzon 4.5 Hz geophones!

60 s

PmS

2555-station Texan array - vertical

correlation => signal

Davenport et al., 2013


IDOR: M7.7 Eastern Russia Earthquake

AIDA Virginia

Davenport et al., in press

148 stations 200-400 m spacing12x12 km array of lines

several thousand aftershocks


AIDA Virginia: Aftershocks

Davenport et al., in press

magnitude 2.0


1 km

0 s

0.10 s

0.05 s

0 s0 s

0.05 s0.05 s

0.10 s0.10 s

1 km 1 km

Wang et al., 2013


magnitude 3.7

source back-projection (3-D reverse time migration)

smallest point-source migrated: M(-2)


1 km

0 s

0.10 s

0.05 s

0 s0 s

0.05 s0.05 s

0.10 s0.10 s

1 km 1 km


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



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


IRIS’s current instrumentation and field procedures are 20+ years oldlimits the science that we can do

past decades have seen rapid improvements in technologyimproved instruments are possible

improving technology enables new science

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 methodsSPATIALALIASING

resolutionresolutionresolution

WAVEFIELDSNOT JUST WAVEFORMS

broadband ~$35k>100 kg3-6-hour deploymentsolar power

long periodhigh sensitivity3-componentlarge memoryGPS

Texan~$4k<2 kg3-minute deployment2 D cells power

high frequencymodest sensitivity1-componentsmall memoryinternal clock

combine the best of bothprobably some compromises

efficiency capacity




in IRIS’s FY2014-2018 NSF Cooperative Agreement:

continue providing existing instrument services

and

development of Large N



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 Keranenmarine, OBSIP: use recent workshop (Van Avendonk)

glossy white paper report: Scientific Potential=> NSF, DOE, DOD, USGS, Industry, …



Sources

sources are not in IRIS’s Large N…

budget is a major issuenon-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 budgetenables science that a PI-driven proposal cannot performa community facility, not just a community projecta virtual facility via standing contracts, rather than instrumentation

imaging with non-aliased seismic wavefields large n (and not just sensors) john hole, iris active...

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