Ource Parameters And Seismogenic Analysis Of Earthquakes In Oklahoma

Earthquake source parameters (Focal depth, strike, dip, rake of faults) are of vital importance for the seismogenic analysis of earthquakes.For moderate earthquakes magnitude ranging from M5.0to M6.0,the point source approximation is effective.Especially for earthquakes of smaller than M5.0whose telesismic waveform records have low signal-noise ratio (SNR), the focal depth can be determined by local depth phases such as sPL,and HYPO2000method can also be used when dense local stations available. While for earthquakes of～M6.0,the telesismic waveform records have high SNR which can be observed in global networks to make up the lack of near-stations and then used to invert focal depth and focal mechanism. In1994, Zhao and Hemlberger proposed CAP (Cut And Paste) method based on waveform is applied to invert focal mechanism and focal depth. For small-to-moderate earthquakes with well-distributed stations and high SNR waveform records, local waveform is used to invert focal depth and mechanism. For lager earthquakes, telesismic waveform is used for its high-SNR.In this study,17earthquakes with magnitude ranging from M3.0to M5.7in2010-2013in Oklahoma are studied. Based on local waveform records, CAP method is applied to invert focal depth and mechanism and the result indicates that most of these earthquakes are shallow strike-slip earthquakes along with some thrust events, and the depth is between3km and13km. The M5.6earthquake in Nov,06th2011, the largest earthquake in Oklahoma since last century, caused some loss for local residents. Local and teleseismic waveform are used to invert focal depth and mechanism and the result shows that the M5.6earthquake is strike-slip earthquake and the focal depth is5km. Moreover, we applied HYPO2000method and sPL depth phase to verify the accuracy of focal depth result of CAP inversion for some events. The focal depth result of sPL depth phase and HYPO2000method is consistent with CAP inversion, which demonstrates that most of earthquakes studied in this study are shallow earthquakes.Many researchers proposed that earthquakes in Oklahoma are "induced" earthquakes, which are related to waste-water injection. Based on previous study, a series of earthquakes in Jan,2011maybe triggered earthquakes.The waveform of these earthquakes has some different characteristics from other earthquakes in this area. The P-wave amplitudes are relatively weak and the coda is strong, which is consistent with the characteristics found in this paper. Moreover, the result shows that most of earthquakes in Oklahoma are shallow strike-slip events and the depth is within6km, which is consistent with the depth range of waste-water injection wells. And then we suggest thatmost of these earthquake studied in this paper are shallow strike-slip events and may be related to waste-water injection during shale gas exploration.