Geometry of Strike-Slip faults through Multiple Earthquake Cycles – GeoSMEC

field geology
numerical modeling
fracture experiences

still to come

still to come

NA

The project “ Geometry of Strike-slip faults through Multiple Seismic Cycles ” aims at better understanding how strike-slip fault geometry evolves, from first initiation of cracks to long time scale involving several successive earthquake cycles. A central point of GeoSMEC is to promote a strong cooperation between earthquake geologists, who have a deep knowledge of field observations (earthquake surface rupture, fault geometry), numerical modelers, who master methods to model fault evolution at different time-scales, and the fracture mechanic community, which is studying crack and seismic rupture propagation from both theoretical, experimental and numerical points of views.
One goal of this project is to produce a detailed dataset of field observations about geometry of large magnitude strike-slip earthquakes, including slip distribution and recurrence time. Because large strike-slip events are not frequent, one challenge of GeoSMEC is to document large past ruptures. This dataset will complement existing data and will serve as input for the several modeling approaches proposed in GeoSMEC to tackle issues such as fault nucleation and geometry stability at various time scales. Most of the data currently available do not have the resolution to be used for this purpose. Hence, in GeoSMEC we plan to document 2 to 3 large events (magnitude >7). To do so, we will take benefit of the new high-resolution optical satellite images (sub-metric pixel) to map old ruptures. Preliminary work has shown that under favorable climatic conditions, surface rupture trace can be preserved for thousands of years. Field work will be done in parallel to cross-check our mapping and open paleoseismological trenches to establish time series of earthquakes on the same fault.
Several approaches will be followed, using these data as input.
We will look at the initiation phase of cracks from approaches mixing theoretical and experimental views and also numerical views (discrete element models). At the end, one wants to test if the initial phase of cracking leaves some imprint that is preserve in the geometry of the fault during its further development. Some simple scaling laws between fault geometry and bulk properties of the medium will also be tested at this stage.
Quantifying how much a seismic rupture could promote fault geometry changes, through accumulation of damage for example, is the next step in GeoSMEC. Field observations of earthquake ruptures show that ruptures are not always perfectly localized and that some areas show high density of cracks, suggesting immature fault segments that could evolve through multiple earthquakes and, eventually, change the fault geometry. This effect will be quantified numerically (using BIEM and SEM methods). A challenge will be to successfully implement simultaneously methods that allow to deal with both dynamic aspect of the rupture and with the long time scale of inter-seismic period and multiple ruptures.
Eventually, a kinematic approach will be used to consider the stability of the geometry of large fault systems, depending on the boundary conditions. One specific point of interest is to quantify the ratio of localized versus diffuse deformation when the fault is not optimally oriented relatively to the boundary conditions. Indeed, large quantity of diffuse deformation would impact the quantity of deformation that could be recognized and measured in the field, and consequently the estimation of the rate of deformation.