Scaling of maximum observed magnitudes with geometrical and stress properties of strike-slip faults

Abstract

We test potential scaling between observed maximum earthquake magnitudes along 27 strike-slip faults with various properties including cumulative displacement, mapped fault length, seismogenic thickness, slip rates, and angle between fault strike and maximum horizontal stress. For 75-80% of the data set, the observed maximum scalar moment scales with the product of seismogenic thickness and either cumulative displacement or mapped fault length. Most faults from this population have slip rates >5 mm/yr (interplate faults), cumulative displacement >10 km, and relatively high angles to the maximum horizontal stress orientation. The remaining 20-25% population involves events at some distance from a plate boundary with slip rate <5 mm/yr, cumulative displacements <10 km, and ≈ 45° to the maximum horizontal stress. These earthquakes have larger magnitudes than the previous population, likely because of larger stress drops. The most likely interpretation of the results is that the maximum rupture length, and hence earthquake magnitudes, correlates with the cumulative displacement and the fault surface length. The results also suggest that progressive fault smoothing may lead to decreasing coseismic stress drops.