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Geomechanical Insights Into the Recent Mw 5+ Earthquakes in the Delaware Basin, West Texas

Description: 

The northern Delaware Basin (NDB) in West Texas has undergone decades of shallow and deep wastewater injection by 1200+ wells. Meanwhile, seismicity in the area started proliferating in 2019, with > 300k detected earthquakes so far, including three M_w 5+ ones. Injection-induced pore pressure diffusion and poroelastic stressing are two common mechanisms driving seismicity. In the NDB, however, their relative importance remains unknown, partly due to difficulties in modeling the complicated injection system. Also, unraveling the contributions of the two injection zones to seismicity is an open question specific to the area. Here, relying on our latest hydro-geomechanical modeling method, we offer insights into these two questions via targeted analysis of the three M_w 5+ earthquakes. Both hydraulic diffusivity and focal depth are crucial but poorly constrained. We thus address the uncertainties by sampling various shallow and deep diffusivities and tracking the Coulomb stress (CS) from the epicenters down to 12 km deep to cover a wide focal range. We disaggregate the CS by mechanism into pore pressure and poroelastic components and by source into shallow injection- and deep injection-induced components. By mechanism, we find that in-zone far-field and out-of-zone poroelastic stress far exceeded in-zone pore pressure in driving all three events, with the poroelastic component always making up > 80% of the CS at their origin time, irrespective of diffusivity and focal depth, and nearing 100% at their reported depths. By source, shallow and deep injection respectively dominated the CS at shallower and deeper depths, as expected; surprisingly, within the basement between 6 and 7+ km deep, there exists a crossover depth below which shallow injection outweighs the deep injection again. This crossover depth increases with deep diffusivity but is less sensitive to shallow diffusivity. Based on our modeling and the reported depths, all three events were likely mainly driven by shallow injection. However, considering uncertainties in focal depths, we cannot rule out deep injection as the main driver of these events.

Session: Mechanistic Insights into Fluid-induced Earthquakes from the Laboratory to the Field - I

Type: Oral

Date: 4/15/2025

Presentation Time: 02:45 PM (local time)

Presenting Author: Lei

Student Presenter: No

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