Geophysics and Tectonics Seminar - spring-2022

March 30, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Justin Higa - UCLA

Understanding what controls landslide occurrence is essential for disaster preparedness. Although previous mechanistic models are moderately successful in predicting potential landslides, we still do not fully know what controls their exact location, size, depth, and timing. Importantly, it remains unclear how groundwater flow in weathered bedrock of the critical zone (CZ) will influence shallow landslides through groundwater exfiltration or lateral flow convergence. Here, we investigate how various CZ structures and rainfall histories interplay and influence landslide occurrences. We use an instrumented site and surrounding catchments (~0.1 km^2) near Coos Bay, Oregon, where studies documented the occurrence of shallow landslides in successive years. Here, workers measured the piezometric response at a landslide in 1996 named CB1 and obtained a 35 m borehole to constrain CZ structure. To construct and test the effect of theoretical CZ structures at this site, we first model soil thickness based on non-linear hillslope diffusion. Then, we create three weathered bedrock scenarios: 1) no weathered bedrock, 2) weathered bedrock from bedrock drainage, and 3) weathered bedrock from a topographic stress model, compared to the depth obtained at the borehole. With these structures, we predict saturation at the soil-weathered rock boundary for historical rainfall records using the hydrologic model GEOtop. Then, we model landslides induced by the predicted saturation using a multidimensional slope stability model. Preliminary analysis suggests that while soil thickness exerts a first-order control on the locations of shallow landslides, there are measurable differences in soil saturation and landslide distribution between various CZ structures. Our work implies that groundwater storage capacity in CZs modulate subsurface saturation and control the shallow landslide response to intense rainfall.

March 30, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Liuwei Xu - UCLA

The 21 May 2021 Mw 7.4 Maduo earthquake, one of the largest earthquakes in central Tibet, provides a unique opportunity to study the source process and physical properties of the central plateau. We utilize the slowness enhanced back projection (SEBP) and finite fault inversion (FFI) method which combines body waves, surface waves and 3D ground displacement data from a satellite to image the rupture process and slip distribution on the fault. Our results indicate a bilateral and shallow rupture with a total length of ~160km. We observe some deep slip patches at the deep part of the fault, and these deep slips could be either real slips or artifacts resulting from the inaccurate velocity model. Based on the large uncertainty of these deep slips and low-velocity middle crust from latest tomography studies, we are in favor of the idea that the source region’s real crust should have higher velocity and rigidity at shallow parts than the published models. The uncertainty analysis indicates the rupture front resolved by BP and shallow slips resolved by FFI are reliable. The consistency between large-slip patches and high-frequency radiators shows these patches are also sources of high-frequency signal. The inclusion of ground displacement in both range and azimuth directions helps better constrain the slip distribution on the junction of two east segments. It also helps explore how slip propagates from the main fault to branch fault. The decoupling between large slip patches and dense aftershock areas indicates that during the mainshock more stress is released on regions with larger coseismic slips.

April 6, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Gan Kuhasubpasin - UCLA

Seminar Description coming soon.

April 13, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Jie Deng - UCLA

The ocean accounts for only 0.02 percent of the Earth's total mass. It has long been speculated that the Earth's interior may host a significant amount of water. Previous experimental and theoretical estimates of the water content in the Earth’s mantle span a wide range, from 1 ocean mass to 7 ocean masses. Here, we investigate the water solubility in the two most dominant silicate phases in Earth and super-Earths, MgSiO3 bridgmanite, and post-perovskite. Specifically, we perform the large-scale two-phase molecular dynamics simulations of silicate and supercritical hydrous fluid at conditions relevant to the deep interiors of rocky planets, which are made possible by the machine learning potential of ab initio quality. The trajectories of hydrogen in these simulations directly inform the water solubility. In this talk, I will present my recent findings on the water solubility of bridgmanite and post-perovskite, and discuss the implications for the water storage of Earth and super-Earths.

April 20, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• David James - UCLA

Seminar Description coming soon.

April 20, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Matthew Bogumil - UCLA

Seminar Description coming soon.

April 27, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Krittanon (Pond) Sirorattanakul - CalTech

Seminar Description coming soon.

May 4, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Saeed Mohanna - UCLA

Seminar Description coming soon.

May 4, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Francis Dragulet - UCLA

Seminar Description coming soon.

May 11, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Yufan Xu - UCLA

Seminar Description coming soon.

May 11, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Cy David - UCLA

We present an experimental, theoretical, and numerical characterization of shallow layer magneto-Couette flow (SLMCF), in which applied electric and magnetic fields drive steady circulating flow of a thin electrolyte layer in an open annular channel. We provide an analytical solution in the low Reynolds number limit, for which we find excellent agreement with numerical simulations and laboratory experiments. The azimuthal flow varies inversely with radial distance except at sidewall boundary layers, which scale with the channel aspect ratios. The underlying viscous-Lorentz balance imbues the system with a remarkable property: our macroscopic low-Reynolds SLMCF system is kinematically-reversible, yet contains no moving mechanical parts; induced deformation may be undone by reversing the direction of the electric current. Further, the magneto-Couette system lends itself to useful extensions: introducing radial variation in the magnetic field or fluid depth may afford precise control over radial shear—potentially useful for macroscale rheological measurements, high-shear liquid-metal-mixing, or for experimentally-modeling astrophysical flows with (low-shear) Keplerian profiles.

May 18, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Xiyuan Bao - UCLA

Seminar Description coming soon.

May 25, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Tian Feng - UCLA

Seminar Description coming soon.

May 25, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Travis Gilmore - UCLA

Seminar Description coming soon.

June 1, 2022
noon - 1 p.m.
Geology 1707

Presented By:

• Stacy Larochelle - CalTech

Seminar Description coming soon.