Subduction zones are regions where one tectonic plate dives underneath another. At the contact between the two plates, large thrust faults (megathrust faults) pose major seismic risks to nearby populations. The magnitude of earthquakes and the time between them depends on how the rocks grind past one another along the faults, as well as how this movement varies over time and space. Some of the rock movements can be transmitted within the continental plate through adjacent tectonic faults. Therefore, to better assess the earthquake hazards associated with subduction zones, one needs to study the plate boundary region as a system of key faults. Here the researchers analyze the earthquakes and ground movements associated with the subduction zone located on the west coast of Mexico. This plate boundary has experienced three large earthquakes (magnitude > 7.0) in the last decade. Key portions of the megathrust fault lie under land and at relatively shallow depths. This makes the fault particularly threatening for the population, yet easier to study than in other locations. To unveil the complex tectonics of the region, the team uses high-precision GPS and seismic recordings collected over two decades. The researchers measure the fault strength and identify patterns in space and time in the distribution of small earthquakes. They also investigate slow ground movements and track the interactions of the subduction zone with intracontinental faults. Outcomes of this project improve the understanding of subduction zone tectonics. They also improve seismic hazard assessment in Mexico and other regions threatened by megathrust faults, as in Alaska and the northwestern US. The project fosters a collaboration between The College of New Jersey and Miami University, as well as international collaboration with Mexico. It provides support for an early career female scientist, a graduate student, and training for undergraduate students notably from groups underrepresented in Science.
This research furthers our understanding of subduction megathrust environments. It takes advantage of decadal-long time series in Mexico as well as sophisticated analytical and modeling techniques, such as event template matching and 3D finite-element modeling. It also accounts for recent discoveries, as the observed correlated slow slip episodes (SSEs) and seismicity occurring on a crustal sliver fault that accommodates the partitioning of oblique convergence in Mexico. The Mexico subduction zone presents a shallow slab angle which brings seismogenic and slow-slip source regions close to and beneath land. The study benefits from this geometry which allows for accurate data acquisition. Moreover, SSEs and megathrust earthquakes in Mexico have short recurrence intervals. This enables studying multiple cycles of elastic rebound. The project has three main goals: 1) Investigate temporal variations in interseismic coupling along the Mexican megathrust and potential correlations with seismicity; 2) examine spatial-temporal relationships between SSEs and megathrust earthquakes in 2012, 2014, and 2018; 3) develop a modeling strategy to resolve SSEs and strain accumulation on both the megathrust and a crustal sliver fault. Results from each of these goals have important implications for seismic hazard and risk assessment, and on whether one can quantify how those hazards are changing over time.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
