TriMan: An interactive tool for modeling earthquakes, with applications to the 1992 Landers and 1999 Hector Mine, California earthquakes

Introduction......................................................................................................................... 1 TriMan software package ................................................................................................... 2 The numeric model ......................................................................................................... 3 Inverse modeling with TriMan ....................................................................................... 5 Construction of the inverse problem........................................................................... 5 Smoothing slip distribution......................................................................................... 6 Constrained slip estimates........................................................................................... 7 Estimating error .......................................................................................................... 9 Forward modeling with TriMan.................................................................................... 10 Calculating static stress change ................................................................................ 10 Other tools in TriMan ................................................................................................... 11 Manipulating fault surface models............................................................................ 11 Refining observation data ......................................................................................... 11 Applying TriMan to the Landers – Hector Mine earthquake sequence............................ 12 Geologic setting ............................................................................................................ 12 Model inputs ................................................................................................................. 14 Displacement data: Global Positioning System observations................................... 14 Fault geometry: the Community Fault Model .......................................................... 17 Modeling Landers slip distribution............................................................................... 19 Modeling Hector Mine slip distribution ....................................................................... 25 Modeling the interaction between the Landers and Hector Mine earthquakes............. 29 Discussion and further studies .......................................................................................... 32 Conclusions....................................................................................................................... 33 Acknowledgments............................................................................................................. 33 References cited ................................................................................................................ 34 Appendix A Inverse problem construction..................................................................... 37 Appendix B Smoothing slip distribution ........................................................................ 38 Appendix C Uncertainties in observation data ............................................................... 39 TriMan: An interactive tool for modeling earthquakes, with applications to the 1992 Landers and 1999 Hector Mine, California earthquakes Mark Dyson Senior Integrative Exercise Advisor: Sarah Titus 9 March, 2007 Abstract In this paper I present a suite of software tools, called TriMan, for interactive modeling of earthquake slip distribution and static stress changes in geometrically complex fault systems. The software uses Global Positioning System co-seismic displacement measurements and triangulated fault surface models, and allows users to quickly experiment with model parameters and easily test hypotheses. An application of TriMan to the 1992 Landers and 1999 Hector Mine earthquakes in southern California yields visual representations of the earthquakes’ slip distribution and Landers – Hector Mine stress interaction. The model shows that the Hector Mine slip distribution is correlated with a positive change in Coulomb failure stress on the Hector Mine rupture surface due to the Landers earthquake, a result consistent with many previous studies of the earthquake sequence.In this paper I present a suite of software tools, called TriMan, for interactive modeling of earthquake slip distribution and static stress changes in geometrically complex fault systems. The software uses Global Positioning System co-seismic displacement measurements and triangulated fault surface models, and allows users to quickly experiment with model parameters and easily test hypotheses. An application of TriMan to the 1992 Landers and 1999 Hector Mine earthquakes in southern California yields visual representations of the earthquakes’ slip distribution and Landers – Hector Mine stress interaction. The model shows that the Hector Mine slip distribution is correlated with a positive change in Coulomb failure stress on the Hector Mine rupture surface due to the Landers earthquake, a result consistent with many previous studies of the earthquake sequence.