THIS FRIDAY: Physical Fault Models: Using Rubber Earthquakes to Understand Seismological Stress Drops and Earthquake Nucleation

**** THIS WEEK ****

FRIDAY MARCH 3, 2023 @ 1P PT
Physical Fault Models: Using Rubber Earthquakes to Understand Seismological Stress Drops and Earthquake Nucleation
Will Steinhardt, UC Santa Cruz

Many geophysical systems, including faults, ice sheets, and hill slopes, are predominantly stable, but become unstable catastrophically, with severe societal consequences when they do. The behavior of these systems is often difficult to predict because they involve extreme spatial and temporal scales, accumulating stresses over decades or centuries, but nucleating failure processes in fractions of second, which start at the micron scale but can lead to kilometers of deformation. To explore these systems, I utilize techniques from applied physics to build scaled-down experiments that behave like “physical models”, where a wide range of system properties can be actively tuned to and otherwise impossible observations made. I will describe a scaled, transparent laboratory fault that shares many similarities to traditional biaxial friction experiments, but studies slip events on a fault made out of a transparent rubber instead of rocks. While rubber may seem like an odd material for studying faults, the measured events display the scaling behaviors of natural earthquakes and slow slip events, and using transparent rubber offers a number of unique experimental advantages and possibilities, including: direct imaging of slip at the frictional interface, active control over normal stress heterogeneity, and ruptures that are fully contained within the edges of the fault area. I will show that slow slip events in our system follow earthquake-like scaling, and demonstrate how finite fault effects alter the stress drop of events. In addition, I will discuss preliminary results from this system on the earthquake nucleation process. [more info] [register]

Thursday, March 9, 2023 @ 2P PT
Effective Strategies for Writing Proposal Work Plans for Research Software
Chase Million, Million Concepts

Effective research proposals must persuade review panels that the project objectives can be achieved and that the requested resources are reasonable and sufficient resources for doing so. A clear, plausible work plan is central to this persuasive process. Despite the fact that many research projects require a great deal of software development, the true costs of software development tasks are often underappreciated and underestimated by both proposers and reviewers. Accurately judging and communicating these costs leads to better proposal and project outcomes. We will quickly survey software project scoping, requirements elicitation, and estimation methods appropriate for the pre-proposal phase, then explain how these can be used to generate a strong and convincing work plan. Topics will include vision and scope, concept of operations, and requirements specification documents; work breakdown structures; requirements / task matrices; and Gantt charts. Strategies for maximizing the impact of these artifacts within a research proposal will be discussed, with suggestions for further reading. [more info] [register]

FRIDAY MARCH 10, 2023 @ 1P PST
Fault strength evolution during the seismic cycle: Insights from the laboratory
John Bedford, University of Liverpool

Geophysical evidence suggests that some faults are frictionally strong, in agreement with laboratory measurements of quasi-static frictional strength (μ ≈ 0.6-0.8) for many crustal materials; whereas others studies have found that some faults are weak when compared to laboratory friction values (μ < 0.5). It has also been well documented that fault materials undergo a significant dynamic reduction in frictional strength when the sliding velocity accelerates to earthquake slip rates (on the order of meters per second). In this talk I will review our current understanding of fault strength evolution during the seismic cycle, then I will present results from two recent laboratory studies where we attempt to elucidate some of the dominant controls on fault strength both before and after an earthquake has occurred. Firstly, I will present results from a study where we investigate how geological heterogeneity in fault zones affects fault strength and stability; we find that heterogeneous faults are considerably weaker and more frictionally unstable than compositionally identical faults with an initially homogeneous structure. Then I will present results from some high-velocity friction experiments where we investigate how faults recover their strength after experiencing dynamic weakening during a seismic slip event. Our findings show that fault strength recovery (healing) occurs rapidly after high-velocity slip, which has important implications for our understanding of rupture dynamics and earthquake recurrence. [more info] [register]

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