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The Occurrence of Persistent Seismicity in a Hydraulic-Fracturing Dominated Area During Operational Shutdown

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip IV

Type: Oral

Date: 4/20/2021

Presentation Time: 05:30 PM Pacific

Description: 

Seismicity in NE British Columbia is usually attributed to ongoing resource development, due to its characteristic temporal and spatial clustering. However, for the first time we have been able to detect seismicity not directly related to these operations, due to the global pandemic of COVID-19 where there was an extended period of anthropogenic quiescence. A total of 389 events were detected from April to August 2020 within the Kiskatinaw area of British Columbia, encompassing a period of no hydraulic-fracturing operations during a government-imposed lockdown. During this time period, observed seismicity had a maximum magnitude of M_L 1.2 but lacked temporal clustering that is often characteristic of hydraulic-fracturing induced sequences. Hypocenters occurred within a corridor orientated NW-SE, similar to previous years, with focal depths near the target Montney formation or shallower (<2.5 km). Based on the Gutenberg-Richter relationship, we estimate that a maximum of 21% of the detected events during lockdown may be attributable to natural seismicity, with a further 8% possibly due to dynamic triggering of seismicity from teleseismic events. However, the remaining ~70% of events cannot be attributed to a primary activation process (e.g. tectonic forces, fluid injection) and has no obvious trigger (e.g. enhanced pressurization at the onset of seismicity). We deem this to be latent seismicity, which shows an unusually long delay following an activation processes. We can exclude direct pore-pressure diffusion from the most recent fluid injection, as there is no clear pattern of temporal or spatial seismicity migration. If elevated pore pressure from previous injections became trapped in the subsurface, this could explain the localization of seismicity within an operational corridor, but it does not explain the latency of seismicity on a timescale of months. Aseismic creep on weak surfaces such as faults, in response to tectonic stresses, in addition to trapped elevated pore-pressure could play a role in stress re-loading to sustain the observed pattern of seismicity.

Presenting Author: Rebecca O. Salvage

Student Presenter: No

Authors