Larry D. Brown, Diego Quiros and Anastasija Cabolova Department of Earth and Atmospheric Sciences Cornell University, Ithaca, NY … and AIDA Virginia an AIDA Maine field teams

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 V p,s in 3D Reflection (cmp style) for structure Seismic interferometry, esp. body waves Objectives:

Field Experiments M 5.8 Mineral, Virginia August 23, 2011 M 4.0 Waterboro, Maine October 16, 2012

Z-component 3-component Non-AIDA Aftershocks Mw 5.8 Non-AIDA What is “dense”? Typical aftershock deployment: a few tens of instruments at  X ~ kms to 10’s of kms AIDA: 100’s of instruments At  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 ~ sps Uses standard D cell (2) Battery life ~ 3 days Procedures for changing battery while recording FlexArray Reftek Inc.

Deployment: AIDA VA Key limitations: Battery life Memory

Single event, single station EQ above, multiple stations Spectra 050 hz The Array Advantage 1 hour, multiple stations Chn Dipping Events: Vehicles Flat Events: EQs Single Station Earthquake Obvious from Moveout Chn Array

AIDA Detection Threshold Mw 1.8 USGS M w -0.7 Single Trace Chn 4 AmpdB k-40k High Q, low noise environment

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 Epicenters August 23, 2011 (Modified from C. Bailey) Aftershock zone geology: Piedmont Province crystalline thrust sheets Davenport, Hole et al

Crustal Reflections from Earthquake Sources PmP? P S  x = 200m sec 6 km PxP X Broadside arrivals From another EQ Midpoints EQ Crustal Reflections from Earthquake Sources

Modeling reflections Model with horizontal Reflector at 6 km P direct S direct P reflected A1 A2 A1 A2

Reflection Geometry Aftershocks are in essence a Reverse VSP survey Surface Array Virtual Well  eqk

VSP CMP Imaging Schuster, 2009 Yu and Schuster, 2006

Reverse VSP gather + NMO (t) NWSENE Upper Crustal Reflection P S INLINEXLINE

CRP Processing of rVSP Conventional CMP vs VSP-CRP: Reflection point is function of source AND reflector depths After Hardage, 2002 Single trace as recorded at surface Trace mapped to x, z Multiple sources Multiple recorders Reflection energy Binned and stacked

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 ? 7.5 km  x = 200m 100 ch 1000 ch 4000 ch North Anna

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 North Ana Nuclear Plant Fredericksburg Z-component 3-component

3 component EW NSZ Attenuation Measurements

Surface Waves from Ambient Noise Cross-Correlated with Station 5 Band Pass HzOffset Plot Velocity ~ 3500 ms -1 Processing: Band Pass-es Hz. Station 5 is virtual souce. 5 days stacked. 4.5 Hz phones!

Virtual Surface Seismic Profile (seismic interferometry) Yu and Schuster, 2006 Source location is not needed!

What about P, S from “Ambient Noise”? 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 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: hz

Conclusions Rapid, high density deployments are imminently feasible High precision  seismic locations, source properties High resolution imaging of local structure using Earthquakes as deterministic sources Tomographic P,S imaging (refraction) 3D reflection imaging S and well as P? Earthquakes as stochastic sources Seismic Interferometry Event location, time not required! Possibility of detailed 4D (e.g. time lapse) source region monitoring

Special Thanks to Geophysics Division: RAPID Grant Bruce Beaudoin, Patrick Bastien, Noel Barstow from PASSCAL Student volunteers from James Madison University and Washington and Lee University Vista Software

Areal Array Dx ~ 5 km Dense Linear Array Dx = 200m ME Aftershock 10/27/12 Quiros and Brown Cornell University 11/4/12 Zoom

Location Improvement AIDA Maine