Illuminating faulting complexity of the 2017 Yellowstone (Maple Creek) earthquake swarm

David R. Shelly, & Jeanne L. Hardebeck

Submitted August 7, 2018, SCEC Contribution #8323, 2018 SCEC Annual Meeting Poster #062

The 2017 Maple Creek earthquake swarm was one of the most prolific swarms to occur in the Yellowstone region in the past decades, with more than 2000 earthquakes up to Mw 4.4 cataloged by University of Utah Seismograph Stations (UUSS) between June and September 2017. The swarm occurred just east of Hebgen Lake, within a zone of high seismicity (and previous swarms) extending northwest from the caldera. To gain insight into the mechanics and underlying mechanisms of this swarm, we performed a high resolution seismic analysis. Using the routinely cataloged earthquakes as waveform templates, we detected and precisely located nearly 16,000 earthquakes, about 6 times the number included in the routine catalog. We further utilized the cross-correlation measurements derived from this processing to determine relatively polarities for event pairs and to estimate focal mechanisms for this large population of events, following the technique proposed by Shelly et al. [2016].

The results illuminate a complex network of faults activated progressively during the swarm. The dominant set of faults strikes ENE, with a secondary set striking toward the NW, potentially forming a conjugate fault set. Short-term migration of hypocenters primary expands along ENE-striking faults, and longer-term migration activates new ENE-striking faults toward the NW and SE. Focal mechanisms indicate primarily strike-slip motion with a contribution of normal faulting. Based on these patterns and comparisons with past swarm activity in the area, we hypothesize that this complexity may arise from the diffusion of fluid pressure through a complex network of pre-existing, relatively permeable faults. Thus, fluid-driven earthquake sequences may naturally generate more complex faulting geometries compared to earthquake sequences dominated by stress transfer.

Key Words
earthquake swarms, fluids, relocation, focal mechanisms, fault mechanics

Shelly, D. R., & Hardebeck, J. L. (2018, 08). Illuminating faulting complexity of the 2017 Yellowstone (Maple Creek) earthquake swarm. Poster Presentation at 2018 SCEC Annual Meeting.

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