Absolute Hypocentral Location Improvements With 3D Velocity Model Optimization: Application to Duvernay, Western Canada
Date: 4/24/2019
Time: 08:30 AM
Room: Cascade I
The reliability of absolute hypocentral locations is of paramount importance as they form the basis for characterizing natural and induced seismicity. Apart from acquisition geometry and phase picking errors, velocity model errors are the main source of event location uncertainty, especially on local arrays, commonly used for induced seismic monitoring. We present a methodology for constructing and further calibrating/optimizing a 3D velocity model to reduce uncertainty in event locations recorded in the Duvernay Subscription Array (DSA) in Alberta, Canada. The method involves building an initial 3D velocity model by interpolating numerous P- and S-phase sonic logs from nearby wells. The model is constrained by structural horizon surfaces and formation tops obtained from surface seismic to ensure agreement with actual Earth’s subsurface velocities and their physical complexity. A combination of cross-validation driven outlier removal and a smoothing operator via an elliptical inverse distance weighted exponential function, help remove poor data and limit unrealistic velocity contrasts. We also calculate station statics and include them in a grid search location algorithm utilizing the new 3D model to relocate the existing event catalog in the DSA network that had initially been located using a simple 1D velocity model. The relocated events show higher precision as they result in tighter clusters with reduced RMS residuals and lower station phase residuals. They also show higher accuracy as they provide better agreement with common events in well-constrained microseismic catalogs. As expected for surface monitoring, the velocity model optimization affects the depths of the events more severely than their lateral positions, which are more stable. The azimuthal coverage and redundancy from addition of potential extra stations can further lower the location uncertainty caused by the configuration bias and arrival-time picking errors.
Presenting Author: Sepideh Karimi
Authors
Yoones Vaezi yoonesvaezi@nanometrics.ca Nanometrics Inc., Ottawa, Ontario, Canada Corresponding Author
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Aaron Booterbaugh aaronbooterbaugh@nanometrics.ca Nanometrics Inc., Ottawa, Ontario, Canada |
Mark Stacey markstacey@nanometrics.ca Nanometrics Inc., Ottawa, Ontario, Canada |
Sepideh Karimi sepidehkarimi@nanometrics.ca Nanometrics Inc., Ottawa, Ontario, Canada Presenting Author
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Dario Baturan dariobaturan@nanometrics.ca Nanometrics Inc., Ottawa, Ontario, Canada |
Absolute Hypocentral Location Improvements With 3D Velocity Model Optimization: Application to Duvernay, Western Canada
Category
From Drifting to Anchored: Advances in Improving Absolute Hypocenter Location Accuracy for Natural, Induced and Explosion Seismic Events