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Roles of Aseismic Slip and Earthquake Interactions in the Evolution of Induced Earthquake Sequences

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

Type: Oral

Date: 4/19/2021

Presentation Time: 05:30 PM Pacific

Description: 

In July 2014, an induced earthquake sequence occurred near Guthrie, Oklahoma following rapidly increased injection at a nearby injection well (Chen et al., 2018). The sequence occurred from early 2014 to late 2015 with over 600 earthquakes between M2 and M4. Rapid fault activation in July 2014 led to diffusive migration. The largest earthquake (M4) occurred in April 2015, towards the end of the sequence. Chen & Abercrombie (2020) performed detailed source parameter analyses using a stacking approach, and found that earthquakes near the beginning of the sequence had lower stress drop. Here we integrate new results from statistical modeling, detailed analyses of rupture directivity and source radius to interpret the roles of aseismic slip and earthquake interactions in the spatiotemporal evolution of the induced earthquake sequence. ETAS (Epidemic-Type-Aftershock-Sequence) modeling indicates three major states of aseismic forcing. The first two stages of aseismic forcing occurred at the beginning of the sequence following rapid increase in injection rate, likely due to fluid induced stress changes. However, the third stage of aseismic forcing occurred during a period with decreased injection rate. High resolution location indicates linear migration along the main fault during the third stage. Rupture modeling suggests several isolated M3 earthquakes (with their own aftershocks) along the linear migration path. These results suggest that an aseismic slip episode likely occurred during this stage. Aseismic forcing rate significantly decreased after the third stage. The largest (M4) earthquake occurred during the time period with low aseismic forcing rate, its early aftershock locations are consistent with rupture directivity to SE. We use empirical Green’s function (EGF) analysis to calculate source time functions and hence rupture directivity of other events (M2-M4) to investigate the roles of earthquake interactions in the sequence evolution. Overall, our integrated analyses suggest that multiple triggering processes are involved in induced earthquake sequences.

Presenting Author: Xiaowei Chen

Student Presenter: No

Authors