Inconsistencies and lurking pitfalls in the magnitude-frequency distribution of high-resolution earthquake catalogs

Marcus Herrmann, & Warner Marzocchi

Published August 15, 2020, SCEC Contribution #10756, 2020 SCEC Annual Meeting Poster #087 (PDF)

Earthquake catalogs describe the distribution of earthquakes in space, time, and magnitude, which is essential information for statistical analysis, earthquake forecasting, and seismic hazard/risk assessment. With the availability of high-resolution (HR) catalogs arises the expectation of benefiting from the abundance of complementary microearthquakes in many aspects. Here we investigate whether these microearthquakes offer a better foundation for the statistical analysis of the magnitude-frequency distribution (MFD). We probe several HR catalogs such as of the 2019 Ridgecrest sequence, the 2009 L'Aquila sequence, and of whole Southern California. We explore whether the MFD of such catalogs is consistent with the scaling relation of Gutenberg-Richter (GR). The slope of the GR relation (b-value) is only meaningful when the magnitudes above the estimated completeness level, Mc, are distributed exponentially. We determine when the MFD departs from an exponential distribution with a statistical hypothesis test and use those departures to explore MFD inconsistencies. We find that HR catalogs do usually not preserve the exponential MFD toward low magnitudes. In fact, they depart at a similar Mc level as MFDs of conventional catalogs. These departures are mostly due to an improper mixing of different magnitude types, spatio-temporal incompleteness, or recording/processing issues; they are not detected by common Mc estimation methods. We conclude that the extrapolation of the exponential GR relation to lower magnitudes cannot be taken for granted, and that HR catalogs pose subtle new challenges and lurking pitfalls that may hamper their proper use. Our findings have implications for both HR catalog producers and modelers that use MFDs of such catalogs.

Key Words
statistical seismology,magnitude-frequency distribution,earthquake catalog,earthquake statistics,hypothesis testing,completeness

Citation
Herrmann, M., & Marzocchi, W. (2020, 08). Inconsistencies and lurking pitfalls in the magnitude-frequency distribution of high-resolution earthquake catalogs. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)