Toward a Regional 3D Velocity Model for the Fort Worth Basin Using Local and Regional Arrival Times and Converted Waves

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Earthquake catalogs for the Fort Worth Basin, developed since wastewater injection induced events began in 2008, rely on traditional 1-dimensional (1D) compressional and shear velocity models that broadly mimic the true 3-dimensional (3D) nature of the oil and gas basin. We report progress on efforts to combine the local and regional phase data to invert for regional 3D compressional and shear velocity with goals to improve location capabilities and map heterogeneity within the units directly perturbed by wastewater injection-related processes. Local earthquake catalogs like the North Texas Earthquake Study (NTXES) include thousands of P- and S-wave arrival times, but due to station configuration and the small magnitude (<3) of most events, the raypath data is primarily upgoing waves. Regional earthquake catalogs systematically include regional and hence downgoing waves. However, the Fort Worth Basin has only experienced 34 magnitude 3+ earthquakes, limiting the size of the regional phase dataset. Previous efforts to develop 3D velocity models in this basin using local earthquake double-difference tomography approaches relied solely on the NTXES catalog and were unsuccessful. Significant velocity and earthquake depth trade-offs could not be resolved due to a lack of downing waves and crossing paths. Two additional datasets now can be used: 1) shallow velocity independently constrained by ambient noise work and Vs30 data modify the starting 1D model; 2) additional regional phase data exists for smaller earthquakes recorded by TexNet. We present updated inversion results using local and regional phase data. The arrival times of a strong S-to-P converted phase, common to many sedimentary basins with induced earthquakes, can be incorporated in the joint inversion, and we present some ideas on how to use this phase to better constrain earthquake location.

Presenting Author: Heather R. DeShon

Authors