资源环境科技发展态势分析平台

We demonstrate the complex source process of a potentially induced Mw 4.0 earthquake near Guthrie, Oklahoma. Relative source time functions (RSTFs), retrieved using a time domain empirical Green's function (EGF) deconvolution method, show clear evidence of rupture complexity with the presence of multiple pulses and systematic azimuthal variations. Directivity analysis reveals a well-defined rupture propagation at similar to 120 degrees toward the southeast. Detailed modeling of the RSTFs results in a four-subevent model spanning similar to 1 s in time and similar to 1.5 km in space, in which the earthquake ruptured four successive slip episodes unilaterally to the southeast. Multiple EGF spectral ratio analysis also shows significant complexity as evidenced by azimuth-dependent deviations from the omega-square (Brune) model. The observations of the concentration of early aftershocks at the periphery of the inferred rupture model along the rupture direction and amplified ground motions at stations to the southeast can both be well explained by the directivity effect.

Plain Language Summary To better understand the rupture growth and development of induced earthquakes in Oklahoma, we provide a comprehensive analysis of the rupture process of an Mw 4.0 earthquake from an earthquake sequence near Guthrie, Oklahoma, that was previously found to show correlation with nearby wastewater injection activity. Using advanced techniques in both the time and frequency domains, we show that this earthquake ruptured four successive slip patches located progressively toward the southeast along the NW-SE-trending fault plane. The source complexity of this earthquake reflects the heterogeneity of fault zone stress, and/or material properties, which may also have prevented the generation of larger earthquakes in this area. The inferred unilateral rupture model also agrees well with the asymmetric distributions of aftershocks and high-frequency ground motions caused by directivity effects. Our results suggest that complexity in source processes scales down to low-magnitude earthquakes for induced earthquakes Oklahoma, implying that geological factors such as geometric or stress heterogeneity in the fault zone might be of primary importance in controlling the rupture growth and development of induced earthquakes.