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Regionalization of ML and Its Relation to Mw

The specification of seismicity rates for Probabilistic Seismic Hazard Analysis often relies on an empirical relation between ML and Mw for small (M < 4) earthquakes, but this requires a consistent definition of ML that accounts for regional differences in wave propagation. The IASPEI ML definition is ML = log10 (A) + 1.11 log10 R + 00189 R - 2.09, where A is the peak horizontal amplitude of a simulated Wood-Anderson seismometer in nm, and R is the hypocentral distance in km (within 1000 km). The first and second distance terms are interpreted as corrections for geometrical spreading and anelastic attenuation, respectively, To regionalize, we propose that events with the same A at short distance (e.g., 10 km) have the same ML, and that only the anelastic attenuation term varies. Given sufficient observations, a plot of the IASPEI ML vs R will exhibit a linear trend, which is sufficient to modify the anelastic attenuation term. The benefits of this approach is that one can always define an ML, even in a relatively aseismic region, if there are sufficient observations with distance. In more seismic regions, similar processing of many events leads to a well determined regional anelastic attenuation correction.

A systematic study of events with M > 3.5 since 2010 has led to the determination of the appropriate anelastic attenuation coefficient for parts of North America. Still there are large regions for which these coefficients are not available because of a lack of earthquakes. We examine the utility of using independently determined Lg-Q values to fill in these gaps. Finally using a database of over 2,500 regional moment tensor inversions for which ML was estimated, the relation between regional ML and Mw is examined for robustness.

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned - V

Type: Oral

Room: Tubughnenq’ 5

Date: 5/2/2024

Presentation Time: 02:45 PM (local time)

Presenting Author: Robert Herrmann

Student Presenter: No

Additional Authors