Objectives:
• 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
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
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Aftershocks
Mw 5.8
Non-AIDA
Anti-alias:
Dx < lmin/2 ~ 100m
Z-component
3-component
Non-AIDA
•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 days
Procedures for changing battery
while recording
FlexArray
Reftek Inc.
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
Key Question: Reactivation or New Fault
Aftershock zone
geology:
Aftershock
Epicenters
Piedmont Province
crystalline thrust
sheets
August 23, 2011
(Modified from C. Bailey)
Davenport, Hole et al
Crustal Reflections from Earthquake Sources
EQ
Midpoints
6 km
0
5
10
sec
Broadside arrivals
From another EQ
Dx = 200m
P
PxP
S
X
PmP?
Modeling reflections
A2
A1
P direct
A2
A1
P reflected
S direct
Model with horizontal
Reflector at 6 km
Reflection Geometry
Virtual
Well
Surface Array
meqk
Aftershocks are in essence a Reverse VSP survey
VSP CMP Imaging
Schuster, 2009
Yu and Schuster, 2006
CRP Processing of rVSP
 Conventional CMP vs VSP-CRP:
 Reflection point is function of source AND reflector depths
After Hardage, 2002
Reflection energy
Trace mapped Multiple sources
Single trace as
Multiple recorders Binned and stacked
recorded at surface to x, z
Mineral VA in 3D
rVSP + NMO (x,y,t)
VA 1 eqk (single fold)
Eqk Gather
VA Earthquake Reflection Image:
3D
Next CRP Stacking:
Mapview: 3 Earthquakes
Ideal
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
What is practical with existing technology?
Dx = 200m
North Anna
100 ch
1000 ch
4000 ch
7.5 km
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
Wait, there’s more….
AIDA 3-C
Fredericksburg
North Ana Nuclear Plant
Z-component
3-component
3 component
EW
Attenuation Measurements
NS
Z
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.
Virtual Surface Seismic Profile
(seismic interferometry)
Yu and Schuster, 2006
Source location is not needed!
What about P, S from “Ambient Noise”?
Virtual Shot Gather
EQ distribution non-isotropic
Virtual Source
Cross-Correlation with Station 13 (7 days)
Resembles EQ time-shifted to the surface
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
Needs for Crustal Imaging
Large numbers (1000’s)
Long lasting (months)
Easily deployable
Self locating
3C
Sensors: 0.1-100hz
ME Aftershock 10/27/12
Areal Array
Dx ~ 5 km
Quiros and Brown
Cornell University 11/4/12
Dense Linear Array
Dx = 200m
Zoom
Location Improvement
AIDA Maine