What does an 'average' large subduction earthquake look like?

Men-Andrin Meier, Jean-Paul Ampuero, & Thomas H. Heaton

Submitted August 15, 2017, SCEC Contribution #7705, 2017 SCEC Annual Meeting Poster #063

When we study individual earthquakes we often notice and report 'peculiarities', or unexpected rupture behavior. This implies that there is a 'normal' or average earthquake behavior from which such events deviate. From an observational perspective, however, this normal behavior is not well constrained. Rather, our expectations are typically driven by conceptual models, such as those of self-similar pulses and cracks. In this study we try to establish the average temporal behavior of large subduction zone earthquakes. We use three data sets of inferred earthquake source time functions (STFs) with Mw>=7. We find that - despite the large variability of individual events - such large ruptures share a typical universal behavior. The typical STF is nearly triangular and symmetric. We compare STFs in a range of magnitude bins and find that, after re-scaling, the median STFs are nearly identical. This scalability, however, does not imply 'physical similarity' in the sense of Aki 1967. In fact, the observed linear moment rate growth stands in contrast to the quadratic growth predicted by self-similar pulse and crack models. This discrepancy suggests that these large events behave differently from the smaller Mw<7 events for which self-similar scaling is well established with abundant data. Furthermore, the deviations from the median STF behavior are multiplicative rather than additive, i.e. they are directly proportional to the STF amplitudes and, consequently, larger for larger events. Smaller and larger earthquakes are statistically indistinguishable until the smaller events reach peak moment rates. We discuss how these observations provide constraints for various aspects of earthquake rupture physics, and the implications they have for earthquake early warning efforts.

Key Words
Earthquake rupture evolution, scalability, predictability

Meier, M., Ampuero, J., & Heaton, T. H. (2017, 08). What does an 'average' large subduction earthquake look like?. Poster Presentation at 2017 SCEC Annual Meeting.

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