Post on 11-Jan-2016
• 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:
Z-component3-componentNon-AIDA
AftershocksMw 5.8Non-AIDA
Typical aftershock deployment: a few tens of instruments at X ~ kms to 10’s of kms
AIDA: 100’s of instrumentsAt x ~ 200 m
Anti-alias:x < min/2 ~ 100m
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•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 daysProcedures for changing battery while recording
FlexArray
Reftek Inc.
Aftershock Hypocenters using AIDA
Locations for >200aftershocks from Aug 27-Sept 9, 2011
Strike ~26°Dip ~52° SE
Data misfits < 40ms, ~200m in given velocity model
Davenport, Hole et al
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
PmP?
PS
x = 200m
0
10
5se
c
6 km
PxP
XBroadside arrivals From another EQ
Midpoints
EQ
Modeling reflections
Model with horizontalReflector at 6 km
P direct
S direct
P reflected
A1
A2 A1 A2
Aftershocks are in essence a Reverse VSP survey
Surface ArrayVirtual
Well
eqk
Schuster, 2009
Yu and Schuster, 2006
Conventional CMP vs VSP-CRP: Reflection point is function of source AND reflector depths
After Hardage, 2002
Single trace asrecorded at surface
Trace mapped to x, z
Multiple sourcesMultiple recorders
Reflection energyBinned and stacked
rVSP + NMO (x,y,t)VA 1 eqk (single fold)
Eqk Gather
Mapview: 3 Earthquakes
Example:
Oyo GSR
1 month at 500 spsGPS onboardCell QC, programmable
> 4000 channels deployed in oil exploration
7.5 km
x = 200m
100 ch
1000 ch
4000 ch
North Anna
Quiros and BrownCornell University 11/4/12
North Ana Nuclear Plant
Fredericksburg
Z-component3-component
EW NS Z
Attenuation Measurements
Surface Waves from Ambient Noise
Cross-Correlated withStation 5
Band Pass 0.01-1.6 Hz Offset PlotVelocity ~ 3500 ms-1
Processing: Band Pass-es 0.001-6 Hz. Station 5 is virtual souce. 5 days stacked.
4.5 Hz phones!
Yu and Schuster, 2006
Source location is not needed!
Virtual Source
EQ distribution non-isotropic
Cross-Correlation with Station 13 (7 days) Resembles EQ time-shifted to the surface
Virtual Shot Gather
Applications: Aftershocks
3D seismic structureVolcano seismicity
3D magmatic structure Induced microseismicity
3D P and S refraction&reflection
Noisy environment?Detection threshold?Adv/Disadv vs borehole?
4D
Needs for Crustal ImagingLarge numbers (1000’s)Long lasting (months)Easily deployableSelf locating3CSensors: 0.1-100hz
Areal ArrayDx ~ 5 km
Dense Linear ArrayDx = 200m
Quiros and BrownCornell University 11/4/12
Zoom
AIDA Maine