Exciting news! We're transitioning to the Statewide California Earthquake Center. Our new website is under construction, but we'll continue using this website for SCEC business in the meantime. We're also archiving the Southern Center site to preserve its rich history. A new and improved platform is coming soon!

The Effect of Slip Variability on Earthquake Slip-length Scaling

Jing Liu, & Thomas H. Heaton

Submitted 2002, SCEC Contribution #686

There has been debate whether average slip in long ruptures should scale with rupture length L, or with rupture width W. This scaling discussion is equivalent to asking whether average stress drop ɥɄ, which is sometimes considered an intrinsic frictional property of a fault, is approximately constant over a wide range of earthquake sizes. In this paper, we examine slip-length scaling relations using a simplified 1-D model of spatially heterogeneous slip. The spatially heterogeneous slip is characterized by a stochastic function with a Fourier spectrum , that decays as k-É—, where k is the wavenumber and É— is a parameter that describes the spatial smoothness of slip. We adopt the simple rule that an individual earthquake rupture consists of only one spatially continuous segment of slip (that is, earthquakes are not generally separable into multiple disconnected segments of slip). In this model, the slip-length scaling relation is intimately related to the spatial heterogeneity of the slip. That is, average slip scales with L 0.8É—-0.25 for 0.5ÑTÉ—ÑT1.5. In this simple class of models, linear scaling of average slip with rupture length only occurs when É— is about 1.5, which is a relatively smooth spatial distribution of slip. We investigate suites of simulated ruptures with different smoothness and we show that faults with large slip heterogeneity tend to have higher /L ratios than those with spatially smooth slip. The model also predicts that rougher faults tend to generate larger numbers of small earthquakes, whereas smooth faults may have a uniform size distribution of earthquakes. This simple 1-dimensional fault model suggests that some aspects of stress drop scaling are a consequence of whatever is responsible for the spatial heterogeneity of slip in earthquakes.

Liu, J., & Heaton, T. H. (2002). The Effect of Slip Variability on Earthquake Slip-length Scaling. Bulletin of the Seismological Society of America, (submitted).