• 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

………………….………………….………………….………………….………………….………………….………………….………………….………………….………………….………………….………………….

•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