accuracy and uncertainty of texnet absolute...
TRANSCRIPT
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Accuracy and Uncertainty of TexNet Absolute Seismic Event Location in West Texas
Anthony Lomax ALomax Scientifc
Mouans-Sartoux, France [email protected]
Alexandros SavvaidisBureau of Economic Geology
The University of Texas at [email protected]
2019 Annual Meeting23-26 April 2019, Seattle
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6km
Where are the earthquakes?
critical to monitoringand explaining
human-inducedseismicity
P, S
P, SP, SP, S
P, S
Problems: stations only at surface + velocity model error
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modelerror model
error
stations
Problem: stations only at surface → horizontal rays at depth
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ray paths?
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stations
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ray pathsmodelerror model
error
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Problem: velocity model error → incorrect times and rays
stations
ray paths modelerror
Surface stations + model error → large hypocentral error
modelerror
stations
West Texas, Delaware Basin study area
Delaware Basin
An increase in induced seismicity inthe central U.S. since 2009 led to
establishment of the TexNet seismic-monitoring program in Texas.
One of the largest petroleumproducing areas in the U.S.
→ Hydraulic fracturing→ Waste water disposal
PB02
West Texas, Delaware Basin study area
TexNet seismicity 2017-2018M = 0.3 → 3.7
PB3D model (Huang et al., 2019)
12km
25km
25-50km
Delaware Basin
PB02
West Texas, Delaware Basin study area
TexNet seismicity 2017-2018M = 0.3 → 3.7
PB3D model (Huang et al., 2019)
12km
25km
Deepening of hypocenterswith distance from stations!
Delaware Basin
~4+ kmepicentershift
Single event absolute errors – Diferent models, station sets
PB02
Random N/2 stations excluded in turn, PB02 may be excluded25-50km station spacing
4 km
PB02
~4+ kmepicentershift
PB02
~5+ kmdepth shift
Single event absolute errors – Diferent models, station setsRandom N/2 stations excluded in turn
4 km 6km
25-50km station spacing
6km
Best: calibration with ground-truth sources
explosion
dense, nearbynetwork
→ P, S Station Corrections
6km
Best: calibration with ground-truth sources
explosion
dense, nearbynetwork
→ P, S Station Corrections
6km
Assume hydraulic fracturing may cause earthquakes
→ Probabilistic, Proxy Ground-Truth(PPGT) Station Corrections
→ Proxy Ground-Truth
12km
Probabilistic, Proxy Ground-Truth corrections from fracturing
PB02
~1000 events near PB02
distancetime
Based on literature + absolute error analysisParameters optimized with grid search
hydraulic fracturing wells
Association likelihood
Probabilistic, Proxy Ground-Truth corrections from fracturing
~900 associations fracturing jobs→events
12km
distancetime
PB02
Association likelihood
Association likelihood
12km
supports assumption: fracturing may cause earthquakes
test reverse time: earthquake→fracturing (a-causal)
Probabilistic, Proxy Ground-Truth corrections from fracturing
→ always fewer a-causal associations✓
6km
Assume fracturing may cause earthquakes → Proxy ground truth
→ PPGT Station Corrections
P, SP, S
Proxy ground truth corrections from fracturing wells Probabilistic, Proxy Ground-Truth corrections from fracturing
Referencelocations
PPGTcorrections
SSSTcorrections
12km
25kmPB02
TexNet seismicity 2017-2018, PB3D model
Referencelocations
wastewater injectionfracturing
Distance from PB02 (km)
Distance from PB02 (km)
Distance from PB02 (km)
Dept
h (k
m)
Dept
h (k
m)
Dept
h (k
m)
count
count
count
Proxy ground truth corrections from fracturing wells Probabilistic, Proxy Ground-Truth corrections from fracturing
Referencelocations
PPGTcorrections
SSSTcorrections
12km
25kmPB02
TexNet seismicity 2017-2018, PB3D model
Referencelocations
wastewater injectionfracturing
Distance from PB02 (km)
Distance from PB02 (km)
Distance from PB02 (km)
Dept
h (k
m)
Dept
h (k
m)
Dept
h (k
m)
count
count
count
Proxy ground truth corrections from fracturing wells Probabilistic, Proxy Ground-Truth corrections from fracturing
Referencelocations
PPGTcorrections
SSSTcorrections
12km
25kmPB02
TexNet seismicity 2017-2018, PB3D model
Referencelocations
wastewater injectionfracturing
Distance from PB02 (km)
Distance from PB02 (km)
Distance from PB02 (km)
Dept
h (k
m)
Dept
h (k
m)
Dept
h (k
m)
count
count
count
Proxy ground truth corrections from fracturing wells Probabilistic, Proxy Ground-Truth corrections from fracturing
Referencelocations
PPGTcorrections
SSSTcorrections
12km
25kmPB02
TexNet seismicity 2017-2018, PB3D model
Referencelocations
wastewater injectionfracturing
Distance from PB02 (km)
Distance from PB02 (km)
Distance from PB02 (km)
Dept
h (k
m)
Dept
h (k
m)
Dept
h (k
m)
count
count
count
✓
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Accuracy and Uncertainty of TexNet Absolute Seismic Event Location in West Texas
Anthony LomaxALomax Scientifc
Mouans-Sartoux, France [email protected]
Alexandros SavvaidisBureau of Economic Geology
The University of Texas at [email protected]
Conclusions: ● Accurate absolute location of seismic events isdifcult but critical to monitoring and explaininghuman-induced seismicity. ● For the Delaware Basin, western Texas, relocationusing diferent velocity models and station subsetsshows 4–5 km absolute epicentral and depth error. ● We associate fracturing and seismicity to developProbabil ist ic Proxy, Ground-Truth stationcorrections to improve absolute event locations. ● Always fewer a-causal associations: supportsassumption fracturing may cause earthquakes. ● Spatial patterns and statistics of west Texasseismicity relocated with PPGT corrections suggestimprovements in absolute location accuracy.
2019 Annual Meeting23-26 April 2019, Seattle
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