Research & Projects

Our goal is to calibrate a distinct element method (DEM) model that effectively represents the styles and patterns of coseismic deformation in the near-surface for a range of soil and sediment properties.

We aim to run a large suite of DEM models that evaluate the influence of fault dip, sediment depth, and sediment strength mechanics on the resultant ground surface deformation.

We aim to construct robust statistical relationships of model parameters to patterns of ground surface deformation that will help us support Probabilistic Fault Displacement Hazard Assessments (PFDHA).

Publications

Chiama, K., Chauvin, B., Plesch, A., Moss, R., Shaw J. H. (2023) Geomechanical modeling of ground surface deformation associated with thrust and reverse‐fault earthquakes: A distinct element approach. Bulletin of the Seismological Society of America; 113(4), 1702–1723. doi: https://doi.org/10.1785/0120220264.

Animations

We use Particle Flow Code (PFC2D, version 6.00 & 7.00) to construct our models from Itasca.

This gif depicts one of our dense, 10 m deep, homogeneous sediment models on a 20º fault.

Each sedimentary layer is 1 m deep and has the same sediment mechanics throughout. A backthrust forms from the tip of the fault seed.

This gif depicts the same model as above but shows the shear bands propagating from the fault towards the surface. We bond our particles using the parallel bond contact model from Itasca with cohesion and tensile strength for the sediment mechanics. Red depicts bonded particles, navy are bonds broken in tension, purple are bonds broken in shear, and light blue are entirely broken contact bonds.

DEM Model Calibrations

Cole & Lade (1984)

Figure from Chiama et al. (2023) BSSA.

We calibrated our 2D DEM model and sediment mechanics to the analog sandbox fault model from Cole & Lade (1984). This allowed us to identify a range of DEM micro-parameters that replicate natural phenomenon.

Bransby et al. (2008) and Garcia & Bray (2018)

Figure from Chiama et al. (2023) BSSA

We performed a second calibration to the analog sandbox fault model from Bransby et al. (2008) and the 3D DEM model from Garcia & Bray (2018). This allowed us to calibrate the porosity and density of our sediment assemblage.

Fig. 11 from Chiama et al. (2023) published in BSSA.

Fault Scarp Classifications

A large suite of 2D DEM models allows us to explore the influence of fault dip angles, sediment strength mechanics, and sediment depth on the resultant fault scarp morphology.

We found that there are 3 main classes of fault scarp morphology in our experiments:

Monoclinal Scarps,
Pressure Ridge,
Simple Scarps.

Each of these classes has a case where the scarp is modified by hanging wall collapse.

The scarp class is dependent on the accumulation of slip on a fault, the fault dip angle, and the sediment strength mechanics.

Fig. 12 from Chiama et al. (2023) published in BSSA.

Scarp Class and Surface Deformation Characteristics

We can evalaute the scarp class and ground surface deformation characteristics throughout the slip on the 2D DEM models.

Each of the 3 main scarp classes has a unique set of characteristics such as fault scarp vertical displacement, deformation zone width, and scarp dip angle. The vertical displacement in this figure is represented as the uplifted top of scarp (Us) minus the vertical displacement at depth (Ud).

This will allow us to develop predictive relationships of ground surface deformation for estimated earthquake magnitudes for a given field site. We are working in conjuction with PFDHA to supplement current datasets of fault displacement hazards.

For more DEM models and animations, see DEM tab!

DEM model animations

Project 2

Organized & led the Harvard University, Dept. of Earth and Planetary Sciences Graduate Student Field Trip - Iceland 2023.

Objectives

Organized and led a Harvard University, Dept. of Earth and Planetary Sciences graduate student field trip to Iceland in Summer 2023.

Support department bonding in a rich geological environment that incorporated field work, volcanology, glaciology, atmospheric dynamics, climatology, and tectonics.

Results

This was the first, large field trip that the department had hosted since the start of the COIVD-19 pandemic. 42 students attended the trip to Iceland from August 10th - 19th and traveled all over the southern coast of the island, including to the Westman Islands. Each student researched a topic on either Icelandic culture or within their scientific field to present on the trip and foster discussions. Students reported feeling much more comfortable returning to the office after the trip and were enthusiastic about the relationships they developed with one another.

Student organizers included (left to right): Andrea Salazar, Kristen Chiama, Robert Welch.

Check out some of our trip photos!

We visited sites such as:

the 2023 Litli-Hrútur eruption,
the 1973 Eldfell eruption in the Westman Islands,
Eyjafjallajökull,
Þakgil,
Thórsmörk,
Vatnajökull,
Þingvellir,
Blue Lagoon,
Carbfix for insights into carbon sequestration and geothermal energy in Iceland,
And tons of other interesting places!

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