Research projects

Hi! This is the project I’ve just started for my postdoc. We’re using seismic reflection data from previous studies to investigate the Taltal seismic gap in northern Chile and the region affected by the Maule earthquake in central–southern Chile. Stay tuned for results!

Here you can read about the work that my colleagues have done in the area using pressure sensors (~seafloor GPS) and oceanographic moorings with multiple instruments: LINK

Like in many other subduction zone systems, in south Chile the obliquity of the subduction transfers stress to the continent that is partitioned as compression and shear stress. The shear stress is parallel to the trench and creates strike-slip systems in the overriding plate. In south Chile, this strike-slip system is known as the Liquiñe-Ofqui fault zone. 

One problem in mapping the Liquiñe-Ofqui fault zone is that south Chile has a lot of vegetation, rainy weather, and sections underwater, so geophysics comes in handy. Our efforts are currently focused on interpreting seismic reflection data collected in the Gulf of Ancud in 2002.

Our preliminary observations reveal deformation within the fluvial and glaciomarine sediments that compose the shallow layers of the basin. The trace of the Liquiñe-Ofqui fault shows a negative flower structure, encompassed by extensional deformation evident through normal faulting. These faults extend to the surface and look fresh, indicating recent activity and an ongoing active system.

Plain Language Summary
The outer layer of the Earth is broken into tectonic plates. The top part of these plates is the crust. In this work, we study the crust of an oceanic plate to understand how plates sink into the mantle—known as subduction. The thickness of the oceanic crust affects how difficult it is for the plate to sink, since thicker, low-density crust floats more in the mantle. People think that the subducting plate can be so buoyant that it fails to sink at a normal rate and, in the mantle, maintains a flat geometry—called a flat-slab.

Oceanic crustal thickness varies significantly, and it is easier to measure before subduction begins. The challenge is that, to study its effect on buoyancy, we need measurements of crust that is already deep in the mantle. In this study, we provide the first estimate of the oceanic plate’s crustal thickness within the mantle beneath Perú and Chile.

We find that crustal thickness measurements before and after subduction are generally similar. However, in flat-slab regions, thickened crust extends across broad areas. Thus, we propose that understanding flat-slab dynamics requires studying (1) crustal thickness within the already subducted plate and (2) the spatial extent of thickening.

(This is my CIDER project!)

When I began studying earthquakes, I only knew about the stick-slip model, and that was it. Now, we know that fault slip occurs across a broad range of rates, encompassing regular earthquakes to slow slip events (SSEs). Researchers have developed computational earthquake cycle models to investigate slip rates along the megathrust. They manage to replicate slow slip by incorporating heterogeneous friction and low effective normal stress due to high pore fluid pressure.

Questions

We recognized that factors such as temperature and lithology dependence of frictional properties, as well as their distribution, remain underexplored in SSEs modeling.

• Can we model the recurrence and size of SSEs by changing the lithology and distribution of heterogeneities? 

• What if we can replicate slow-slip through adjustments in frictional properties and distribution, without necessarily requiring high pore fluid pressure? and, if it turns out that we do indeed need pore pressure, do we truly need the high levels that other models employ?

Approach

Using the code HBI from Ozawa et al., 2023, we simplify the subduction interphase into a matrix with patches of different lithology. Based on the exhumed subduction rock record and laboratory experiments, we constrained the interface's structure, lithology, and temperature dependence of frictional properties.

For our study, we are focusing on the Cascadia margin. We plan to vary possible interface patch/matrix lithologies and compare model results to existing seismic and geodetic data to assess the reproducibility of SSE spatial and temporal variability using this heterogeneous interface. 

We expect to have results by the end of the year. My collaborators will be presenting this work as a poster at the AGU fall meeting, 2023.