| Abstrakt: |
The magnitude‐frequency distribution (MFD) describes the relative proportion of earthquake magnitudes and provides vital information for seismic hazard assessment. The b‐value, derived from the MFD, is commonly used to estimate the probability that a future earthquake will exceed a specified magnitude threshold. Improved MFD and b‐value estimates are of great importance in the central and eastern United States where high volumes of fluid injection have contributed to a significant rise in seismicity over the last decade. In this study, we recalculate the magnitudes of 8,775 events for the 2011 Prague, Oklahoma sequence using a relative magnitude approach that depends only on waveform data to calculate magnitudes. We also compare the distribution of successive magnitude differences to the MFD and show that a combination of the magnitude difference distribution (MDFD) and relative magnitudes yields a reliable estimate of b‐value. Using the MDFD and relative magnitudes, we examine the temporal and spatial variations in the b‐value and show that b‐value ranges between ∼0.6 and 0.85 during the aftershock sequence for at least 5 months after the M 5.7 mainshock, though areas surrounding the northeast part of the sequence experience higher b‐values (0.7–0.85) than the southwestern part of the Meeker‐Prague fault where b‐value is the lowest (0.6–0.7). We also identify a cluster of off‐fault events with the highest b‐values in the catalog (0.85). These new estimates of MFD and b‐value will contribute to understanding of the relations between induced and tectonic earthquake sequences and promote discussion regarding the use of b‐value in induced seismic hazard estimation. Plain Language Summary: The magnitude‐frequency distribution and the b‐value are statistical parameters that describe how earthquake magnitudes are distributed in a catalog. These parameters are vital for hazard estimation of induced seismicity in the central and eastern United States, but they are not well understood in this region due to reasons including, but not limited to, catalog incompleteness, magnitude uncertainty between different magnitude types, and variable injection history. In this study, we reevaluate the previously cataloged magnitude estimates using a relative magnitude method to estimate the temporal and spatial variation in b‐value for the 2011 Prague, Oklahoma sequence. With the relative magnitude method, we reestimate magnitude for 81% of the events in the Prague sequence which are then utilized for b‐value estimation. We demonstrate the presence of consistently low b‐values during the aftershock sequence for at least ∼5 months following the mainshock and identify a trend of decreasing b‐value along the Meeker‐Prague fault as distance from the mainshock increases. These observations allow us to compare spatial and temporal b‐value variations of induced sequences to those observed in tectonic sequences. Key Points: The relative magnitude method allows for recalculation of earthquake magnitude without requiring location or geological dataRelative magnitudes combined with the b+ estimator gives a reliable estimate of b‐valueWe identify patterns of spatial and temporal variations in b‐value that are consistent with tectonic sequences [ABSTRACT FROM AUTHOR] |
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