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Investigating microearthquake finite source attributes with IRIS Community Wavefield Demonstration Experiment in Oklahoma

Wenyuan Fan, & Jeff J. McGuire

Published May 21, 2018, SCEC Contribution #8014

Earthquake rupture process can be kinematically described by rupture velocity, duration and spatial extent. These key kinematic source parameters provide important constraints on earthquake physics and rupture dynamics. In particular, core questions in earthquake science can be addressed once these key kinematic properties of small earthquakes are well resolved. However, these parameters of small earthquakes are poorly understood, often limited by available datasets and methodologies. The IRIS Community Wavefield Experiment in Oklahoma deployed $\sim$350 three component nodal stations within 40~${\rm km}^2$ for a month, offering an unprecedented opportunity to test new methodologies and resolve small earthquake finite source properties in high resolution. In this study, we demonstrate the power of the nodal dataset to resolve the variations in the seismic wavefield over the focal sphere due to the finite source attributes of a M2 earthquake within the array. The dense coverage allows us to tightly constrain rupture area using the second moment method even for such a small earthquake. The M2 earthquake was a strike-slip event and unilaterally propagated towards the surface at 90\% local S-wave speed (2.93~km/s). The earthquake lasted $\sim$0.019~s and ruptured 1000~${\rm m}^2$. With the resolved rupture area, the stress-drop of the earthquake is estimated as 7.3~MPa for Mw~2.3. We demonstrate that the maximum and minimum bounds on rupture area are within a factor of two, much lower than typical stress drop uncertainty, despite a suboptimal station distribution. The rupture properties suggest that there is little difference between the M2 Oklahoma earthquake and typical large earthquakes. The new three component nodal systems have great potential for improving the resolution of studies of earthquake source properties.

Fan, W., & McGuire, J. J. (2018). Investigating microearthquake finite source attributes with IRIS Community Wavefield Demonstration Experiment in Oklahoma. Geophysical Journal International, 214(2), 1072-1087. doi: 10.1093/gji/ggy203.

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