Analysis of slip-weakening frictional laws with static restrengthening and their implications on the scaling, asymmetry and mode of dynamic rupture on homogeneous and bi-material interfaces

Dynamic simulations of homogeneous and heterogeneous fault rupture using the finite element method are presented giving rise to both crack-like and pulse-like rupture. We employ various slip-weakening frictional laws to examine their effect on the resulting earthquake rupture speed, size and mode. More complex rupture characteristics were produced with more strongly slip-weakening frictional laws, and the degree of slip-weakening had to be finely tuned to reproduce realistic earthquake rupture characteristics. Rupture propagation on a fault is controlled by the constitutive properties of the fault. A dynamic elasto-plastic constitutive law for the interface friction at the fault is formulated based on the Coulomb failure criterion and applied in a way analogous to non-associated elasto-plasticity. We provide benchmark tests of our method against other reported solutions in the literature. We demonstrate the applicability of our elasto-plastic fault model for modeling dynamic rupture and wave propagation in fault systems, and the rich array of dynamic properties produced by our elasto-plastic finite element fault model. These are governed by a number of model parameters including: the spatial and material heterogeneity of the fault, the fault strength, and not least of all the frictional law employed. Asymmetric bilateral fault rupture was produced for the heterogeneous case, where the degree of heterogeneity influenced the rupture speed in the different propagation directions

Identification of supershear transition mechanisms due to material contrast at bimaterial faults

Numerical modelling of dynamic rupture is conducted along faults separating similar and dissimilar materials. Supershear transition is enhanced in the direction of slip of the stiffer material (the negative direction) due to the bimaterial effect whereby a decrease in normal stress in front of the crack tip supports yielding ahead of the rupture. In the direction of slip of the more compliant material (the positive direction), an increase in normal stress ahead of the rupture tip delays or prevents the supershear transition, whereas the impact of the bimaterial effect on subshear ruptures is to promote rupture in the positive direction due to the tensile stress perturbation behind the rupture tip in this direction. We demonstrate that the material contrast and the parameter S control whether the transition from sub- to supershear velocity (supershear transition) is smooth or follows the Burridge–Andrews mechanism. Supershear transition along interfaces separating dissimilar materials is possible for higher values of the parameter S than supershear transition along material interfaces separating similar materials. The difference between pulse-like and crack-like rupture is small with regard to the supershear transition type

Stress heterogeneities in earthquake rupture experiments with material contrasts

We investigate significant heterogeneous stresses along bimaterial interfaces in laboratory and numerical experiments. These stresses, partially induced by model or experimental configuration, affect the supershear transition length and rupture speed, mode and directivity in uniaxial compression tests and dynamic rupture experiments with bimaterial interfaces. Using numerical simulations we show that normal and tangential stresses at the fault are distorted by the different stress-strain relationships of the materials. This distortion leads to altered supershear transition lengths, higher rupture potencies and amplifies the preference for rupture in the direction of slip of the slower and more compliant material. We demonstrate how this stress-distortion can be decreased in laboratory experiments by using larger specimen samples and in numerical models by using periodic boundary conditions

Recurrence interval statistics of cellular automaton seismicity models

The recurrence interval statistics for regional seismicity follows a universal distribution function, independent of the tectonic setting or average rate of activity (Corral, 2004). The universal function is a modified gamma distribution with power-law scaling of recurrence intervals shorter than the average rate of activity and exponential decay for larger intervals. We employ the method of Corral (2004) to examine the recurrence statistics of a range of cellular automaton earthquake models. The majority of models has an exponential distribution of recurrence intervals, the same as that of a Poisson process. One model, the Olami-Feder-Christensen automaton, has recurrence statistics consistent with regional seismicity for a certain range of the conservation parameter of that model. For conservation parameters in this range, the event size statistics are also consistent with regional seismicity. Models whose dynamics are dominated by characteristic earthquakes do not appear to display universality of recurrence statistics

Trends in seismicity in the CSG producing region of the Surat Basin in Queensland

The Australian continent is generally in a state of compressive stress. Australian earthquakes, for which focal mechanisms have been calculated, are generally reverse-faulting events, consistent with a predominantly compressive tectonic regime. Earthquakes of moderate intensity have been reported in Queensland since the first decades of European settlement; the first reported earthquake occurring in Cape York in 1866. The Central Burnett region, just to the north of the Surat Basin (and on different terrain), remains one of the most active regions of the State, the most recent notable earthquake being in 2015 (Eidsvold, M=5.2 main-shock). Aftershocks of this event continued to be recorded some four years subsequent. Since 1937, a growing number of entities have operated seismic networks within the State, for varying purposes and with equipment of varying instrumental design and capabilities. Campaigns of seismograph installations in the late 1970s and early 1980s improved the detection threshold down to M=3; and as low as M=2.5 in parts of south-eastern Queensland (Cuthbertson and Jaume, 1996). Whilst additional seismograph networks have been periodically installed and operated since that time, the detectability threshold for very small magnitude earthquakes has remained approximately constant. Large amounts of previously uninterpreted data has been used in this study. The study considers the location of sensors and examines the Gutenberg-Richter frequency magnitude relation for Queensland and for the Surat Basin since 1986. It also discusses detection and resolution limits and provides a baseline understanding of natural seismicity and likely rates thereof

Virtual rock laboratory - A grid portal enabling computational geoscience research

Virtual Rock Lab (VRL) is a secure web portal designed to enable users without programming skills to construct and execute ESyS-Particle simulations. The portal covers all steps of the work flow combining interfaces that allow users to create and edit input scripts through dialogues, submit jobs to a supercomputer connected to the AuScope Grid and browse a simulation journal to access past simulations and monitor active ones. Thus, authorised users need nothing more than a computer with a web browser to use the system and require no programming skills

Queensland Earthquake Felt report survey of the public for isoseismal mapping

10 L/metres of folders and chronologically dated paper archives locating Queensland earthquakes and documenting the felt effect of the earthquakes on the public and infrastructure

Validation of using Gumbel Probability Plotting to estimate Gutenberg-Richter seismicity parameters

The Gumbel Type I statistics of extreme events have been successfully used in the past to forecast various natural events such as annual exceedence of design flood level, and hall fall. Some attempts have been made to determine seismicity parameters using the annual maximum magnitude events in historic records. The results from these determinations have invariably been criticized for various reasons, including the perception that the methodology ignores important data, and that the method has no verification basis. This paper address both topics by discussing the principles of the reliably deducing the Gutenberg-Richer seismicity parameters of complete synthetic earthquake calendars, using only the annual maxim