DYNAMICALLY TRIGGERED EARTHQUAKES AND THEIR RELATION TO FLUID INJECTION IN THE CENTRAL UNITED STATES

Earthquake triggering is divided into two mechanisms: Static triggering, caused by near-field static stress changes after fault slip, and dynamic triggering, resulting from stress changes due to seismic waves which can act at large distances. While triggering phenomena have been extensively studied in various seismically active regions, limited attention has been given to the Central United States, where several regions have been susceptible to pore pressure changes and induced earthquakes. This study aims to investigate the impact of major teleseismic earthquakes with magnitudes exceeding 6.5 on seismicity rates in the New Madrid Seismic Zone and Oklahoma region.

To explore high-frequency local triggered events in the study regions, we analyze continuous 24-hour waveform data (12 hours before and after the wave arrival) of teleseismic events. To achieve our objectives, two main approaches are employed: Firstly, we compare seismicity rates before and after the arrival of the teleseismic surface wave. An increased seismicity rate following the teleseismic event, compared to the baseline seismicity, could indicate dynamically triggered events. For event detection, we use two separate methods: 1) STA/LTA and 2) machine learning algorithms (PhaseNet, GPD, EQTransformer). Secondly, we calculate the ratio of high-frequency energy before and after the teleseismic wave arrival. Energy ratios above a certain threshold indicate likely triggered events at a station. Sub-samples of waveform data from the study area are manually examined to ensure consistency with characteristics earthquake seismograms. Additionally, we measure Peak Ground Acceleration (PGV) values to examine the potential relation between triggered events and PGV values at each station. This investigation may uncover the triggering threshold and reveal the stress state of subsurface faults in the study area. Determining the triggering threshold will significantly contribute to hazard mitigation planning in seismic zones.