Scaling Relations of Source Parameters of Earthquakes Occurring on Inland Crustal Mega-Fault Systems

Abstract

We examined a new scaling relation between source area S and seismic moment M 0 for large crustal earthquakes on “mega-fault” systems, including earthquakes with magnitudes larger than M w7.4. We focused on earthquakes that occurred on inland crustal mega-fault systems, such as the 2008 Wenchuan and 2002 Denali earthquakes, and compiled the source parameters using 11 inland crustal earthquakes which analyses of source rupture processes by waveform inversion as well as investigation of surface ruptures via geomorphological surveys. We found that the maximum surface rupture displacement is two to three times larger than the average slip on the source fault, and the length of the surface rupture is equivalent to the length of the source fault. Furthermore, our compiled data shows the displacement of the surface rupture D saturates around 10 m when the length of the surface rupture L reaches 100 km. Assuming that the average width of the source fault W = 18 km (for Japanese inland crustal earthquakes) and the saturated surface displacement D = 10 m, we found that the scaling relations between rupture area S and seismic moment M 0 have three stages. For the first stage, S is proportional to M 0 2/3 for earthquakes smaller than M 0 = 7.5 × 1018 Nm. For the second stage, S ranges from M 0 1/2 to M 0 2/3 , depending on the thickness of the seismogenic zone. For the third stage, S is proportional to M 0 because of the saturation of the slip on the fault. From our compiled data, we derived the third scaling relation between source area S and seismic moment M 0 for inland crustal mega-fault systems to be S (km2) = 1.0 × 10−17 M 0 (Nm), where M 0 > 1.8 × 1020 (Nm).