The magnitude‐frequency distribution (MFD) describes the relative proportion of earthquake magnitudes and provides vital information for seismic hazard assessment. The
This content will become publicly available on December 12, 2024
 Award ID(s):
 2315814
 NSFPAR ID:
 10533634
 Publisher / Repository:
 AGU
 Date Published:
 Format(s):
 Medium: X
 Location:
 San Francisco, CA
 Sponsoring Org:
 National Science Foundation
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Abstract 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 andb ‐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 ofb ‐value. Using the MDFD and relative magnitudes, we examine the temporal and spatial variations in theb ‐value and show thatb ‐value ranges between ∼0.6 and 0.85 during the aftershock sequence for at least 5 months after theM 5.7 mainshock, though areas surrounding the northeast part of the sequence experience higherb ‐values (0.7–0.85) than the southwestern part of the Meeker‐Prague fault whereb ‐value is the lowest (0.6–0.7). We also identify a cluster of off‐fault events with the highestb ‐values in the catalog (0.85). These new estimates of MFD andb ‐value will contribute to understanding of the relations between induced and tectonic earthquake sequences and promote discussion regarding the use ofb ‐value in induced seismic hazard estimation. 
A precise understanding of earthquake magnitudes is vital for accurate calculations of magnitude exceedance probabilities and seismic hazard assessment. However, characterization of earthquake magnitude, particularly for small events, is complicated by differences in network capabilities and procedures. Furthermore, the use of differing magnitude scales for events of various sizes introduces additional challenges and produces disparate magnitude estimates for the same events. To address the need for a consistent magnitude estimation procedure that can accurately estimate magnitude across a wide magnitude range and in diverse tectonic environments, we investigate the use of the relative magnitude method. This approach utilizes amplitude ratios of highly correlated waveforms among numerous interlinked event pairs to compute magnitude for a group of events. While the relative magnitude method is advantageous because it can be applied uniformly in various regions and does not require distance or attenuation corrections, there are several parameters that currently require human decision which may introduce bias. These include acceptable thresholds for signaltonoise ratios and crosscorrelation, filtering procedures, sampling windows, and station selection. Our research focuses on computing new relative magnitudes for events in southern California, including the 2019 Ridgecrest sequence. We investigate the uncertainty that human decision may impose on the resulting magnitudes and compare our results to other magnitude estimation methods. Finally, we present our recommendations for routine procedures that minimize uncertainty and variability in the relative magnitude method, aiming to enhance the utility of this method for future users.more » « less

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