Fall 2021

Fridays at 12:00 PM
E&MS A340


September 24, 2021

Speaker: Valere Lambert, UCSC

Title: Absolute stress levels on mature faults: Bridging insight from the lab and field using physics-based modeling

valere


October 1, 2021

Speaker: Eben (Blake) Hodgin, UC Berkeley

Title: New age constraints from North America's Midcontinent Rift calibrate the timing of rift cessation and inversion, providing insights into far-field control on the geodynamics of rift failure

Eben


October 8, 2021

Speaker: Beck Strauss, NASA

Title: The Case of the Disappearing Dynamo: Constraining the decline of the Moon’s magnetic field through experimental analyses of Apollo samples

Beck


October 15, 2021

Speaker: Matt Wei, University of Rhode Island

Title: Earthquake cycle and segmentation on oceanic transform faults

Abstract: Oceanic transform faults are a significant component of the global plate boundary system and are well known for generating fewer and smaller earthquakes than expected. Detailed studies at a handful of sites support the hypothesis that an abundance of creeping segments is responsible for most of the observed deficiency of earthquakes on those faults. We test this hypothesis on a global scale. We relocate Mw≥5 earthquakes on 138 oceanic transform faults around the world and identify creeping segments on these faults. We demonstrate that creeping segments occur on almost all OTFs, which could explain the deficiency of earthquakes. We also find most of the creeping segments are not associated with any large-scale geological structure, such as fault step-overs, indicating that along-strike variation of fault zone properties may be the main reason of their existence. Synchronization behavior of large earthquakes (rupture of nearby faults close in time for many cycles) has been reported in many fault systems. The general idea is that the faults in the system have similar repeating intervals and are positively coupled through stress interaction. However, many details of such synchronization remain unknown. Here, we explore the static and viscoelastic interactions on oceanic transform faults using two numerical models, both consist of two seismic patches separated by a barrier patch on the fault. The simulation of pure elastic model showed that static stress transfer can lead to synchronization, opposite to the suggestion by Scholz (2010), which was based on results from a spring-slider model using rate-and-state friction. The viscous model consists of a elastic fault and a viscous mantle. The simulation showed that the effective mantle viscosity should be one magnitude lower than what was reported in Hirth & Kohlstedt, (2003) beneath Gofar to achieve synchronization.

Matt


October 22, 2021

Speaker: George Hilley, Stanford University

Title: Building Earth Structures from Earthquakes: Understanding Deformation within the Santa Cruz Mountains Across Space and Time

Abstract: How do earthquakes build mountains and geologic structures? This is an important fundamental question in earth sciences that has implications for hazards posed by motion along active faults. In this talk, I’ll present a decades’ worth of data collection from my group, which image the deformation, uplift, and erosion of the Santa Cruz Mountains over time-scales ranging from decades to millions of years. These myriad data are then used to address two questions — one applied and one fundamental. First, we ask whether topographic and thermochronologic data can be used to estimate the slip rate distribution along reverse faults that bound the western flank of Silicon Valley using models of crustal deformation and erosion. These structures are difficult to characterize directly, because they are either blind or do not preserve sediments that can be used to deduce their slip rates. We find that our methodology for inverting topography for fault slip rates yields estimates for plate-boundary motions and rock erodibilities that agree with published estimates. We infer that these faults are capable of producing a Loma-Prieta type earthquake every 300 years, and so constitute a substantial hazard to Silicon Valley given the proximity and geometry of these faults. Second, we ask whether a small modification to the traditional elastic earthquake-cycle model that allows crust to yield over geologic time-scales can reconcile conflicting information about deformation, uplift, and erosion of the Santa Cruz Mountains when measured over decades versus millions of years. We find that a crustal rheology that includes strain-hardening plasticity successfully bridges observations over these vastly different time-scales. Interestingly, the model implies that interseismic intervals build the mountains in the area, while elastic strain release during earthquakes lowers them, such that interseismic yielding allows the steady accrual of long-term uplift of the range. Our studies show that decadal time-scale measures of surface deformation cannot discriminate the appropriate rheology of the crust — it is only by including geologic observations that we can deduce this information. As such, geologic observations constitute a cornerstone of crustal deformation studies that seek to understand the rheology of Earth’s crust.


October 29, 2021

Speaker: Jessica Hawthorne, University of Oxford

Title: Inferences about fault processes from the sizes and timing of slow and fast earthquakes


November 5, 2021

Speaker: Stefania Soldini, University of Liverpool

Title: The Effect of "Mascons" Interior Mass Distribution onto the Dynamic Environment Around Asteroids


November 12, 2021

Speaker: Lior Rubanenko, Stanford University

Title: Global Morphometrics of Barchan Dunes on Mars Revealed by Artificial Intelligence

Abstract: Barchan dunes are crescentic windblown features that emerge when the sand supply is limited and the wind is approximately unidirectional. The complex morphology of barchan dunes is influenced by of the environmental conditions in which they form. For that reason, barchans are routinely used to investigate arid climates on both Earth and Mars. Motivated to understand how global trends in barchan morphology relate to global and local environmental conditions, we use a convolutional neural network to map and outline barchan dunes on Mars. Our trained model reviewed 137,111 Mars Reconnaissance Orbiter Context Camera (MRO CTX), detecting over a million instances of barchan dunes. From the dunes’ outlines, we derive morphometrics such as dune width, length and horn ratio - and provide an estimate for the dune volume. Our dataset reveals geospatial patterns related to frost coverage and sand supply and is used to infer dune migration directions on a global scale, which are a proxy for the direction of near surface winds.

Lior


November 19, 2021

Speaker: Cauê Borlina, MIT

Title: Understanding the Evolution of the Early Solar System through Paleomagnetism of Meteorites

caue


December 3, 2021

Speaker: Colin R. Meyer, Dartmouth

Title: A thermomechanical model for frozen sediments

Abstract: Ice-infiltrated sediment, known as a frozen fringe, leads to phenomena such as frost heave, ice lenses, and meters of debris-rich ice under glaciers. Understanding the dynamics of frozen fringe development is important as frost heave is responsible for damaging infrastructure at high latitudes; frozen sediments at the base of glaciers can modulate glacier flow, influencing the rate of global sea level rise; and frozen water ice exists within the sediments of the top several meters on Mars and in places on the Moon. Here we study the fluid physics of interstitial freezing water in sediments and focus on the conditions relevant for subglacial and planetary environments. We describe the thermomechanics of liquid water flow through and freezing in ice-saturated frozen sediments. The force balance that governs the frozen fringe thickness depends on the weight of the overlying material, the thermomolecular force between ice and sediments across premelted films of liquid, and the water pressure within liquid films that is required by flow according to Darcy's law. Our model accounts for premelting at ice-sediment contacts, partial ice saturation of the pore space, water flow through the fringe, the thermodynamics of the ice-water-sediment interface, and vertical force balance. We explicitly account for the formation of ice lenses, regions of pure ice that cleave the fringe at the depth where the interparticle force vanishes.

colin