IGPP is pleased to invite you to join its Winter 2024 Seminar Series presentation featuring UC Riverside's Roby Douilly. Dr. Douilly's talk, "Effects of Asymmetric Topography on Rupture Propagation Across Fault Stepover: Case Study of the 2021, Nippes, Haiti Earthquake" will occur at 3pm TUESDAY February 20, 2024.
Time: 3:00 pm, Pacific Time
Location: Revelle Conference Room
Abstract: Complex fault systems, such as the Enriquillo Plantain Garden (EPG) fault system in Hispaniola, are often located in regions with asymmetric topography. This fault system has experienced several destructive earthquakes. A decade after the devastating 2010 earthquake, a M7.2 earthquake struck the western portion of the southern peninsula and led to more than 2,200 deaths. Space geodetic results show that this latest event is composed of both left-lateral strike-slip and thrust motion, but aftershock locations from a local shortperiod network are too diffuse to precisely delineate the segments that participated in this rupture. A few days after the mainshocks, in collaboration with several institutions, we installed 12 broadband stations in the epicentral area, and we precisely relocate aftershocks from August to December 2021. The majority of the aftershocks form three separate clusters with slightly different strike and dip, but the western cluster followed the surface trace of the Ravine du Sud fault, a parallel to the main EPG fault trace. The extensional stepover between the Ravine du Sud fault and the EPG fault has a width of 3-4 km and the 2021 rupture couldn’t propagate across this discontinuity. Previous rupture dynamic studies have investigated the effect of stepover widths on throughgoing rupture, but these studies didn’t examine the influence of topography on the rupture behavior. To investigate the effect of asymmetric topography on rupture dynamics at stepovers, I consider three cases: 1) a flat topography, 2) a positive (mountain) and 3) a negative (basin) topography on only one side of the fault system outside of the stepover. In each case, I use the 3D finite element method to compute the rupture dynamics of these fault systems. The results show a significant time dependent variation of the normal stress for the topography cases as opposed to the flat surface case, which can have an important impact on rupture propagation at the stepover. For a positive topography on the right of the rupture propagation, there is a clamping effect behind the rupture front that prevents the rupture to jump a wider extensional stepover. These results suggest that topography should be considered in dynamic studies with geometric complexities such as stepovers, and perhaps bends and branched fault systems.