Fall 2017

September 29, 2017

Speaker: Jing Luan, UC Berkeley

Title: Enceladus: three-stage limit cycle and current state

Abstract: Enceladus is one of the most popular worlds that might accommodate life outside our own earth. We study its evolutionary path, especially focus on the physical processes that drive Enceladus to its current state. I will also discuss possible applications of these physical processes to other bodies in our solar system. Below is a brief summary of the evolution path for Enceladus.

Eccentricity (e) growth as Enceladus migrates deeper into mean motion resonance with Dione results in increased tidal heating. As the bottom of the ice shell melts, the rate of tidal heating jumps and runaway melting ensues. At the end of run-away melting, the shell's thickness has fallen below the value at which the frequency of free libration equals the orbital mean motion and e has damped to well below its current value. Subsequently, both the shell thickness and e partake in a limit cycle. As e damps toward its minimum value, the shell's thickness asymptotically approaches its resonant value from below.  After minimum e, the shell thickens quickly and e grows even faster.  This cycle is likely to have been repeated multiple times in the past.

Currently, e is much smaller than its equilibrium value corresponding to the shell thickness. Physical libration resonance resolves this mystery, it ensures that the low-e and medium-thickness state is present for most of the time between consecutive limit cycles. It is a robust scenario that avoids fine tuning or extreme parameter choice, and naturally produces episodic stages of high heating, consistent with softening of topographical features on Enceladus.

October 6, 2017

Speaker: Philip Carter, UC Davis

Title: Collisional modification of planetary compositions

Abstract: Models of planet formation help bridge the observational gap between protoplanetary discs and fully formed planetary systems. Our solar system provides key benchmarks for planet formation theories, particularly via detailed compositional information both from the Sun and from meteorites. As observations of exoplanets improve it becomes increasingly important to understand how accretion shapes the compositions of planets. Collisional erosion during the accretion of terrestrial planets has been suggested as an important mechanism for altering planetary compositions, which might explain observed differences between Earth and chondrites. I will present the results of simulations of terrestrial planet formation which include imperfect accretion and track compositional information, and simulations of planetary embryo collisions which trace planetary crusts. I will show that the accretion process during the intermediate growth phase can naturally lead to changes in the bulk compositions of planetary bodies, and discuss measurable consequences of two contrasting planet formation models.

October 13, 2017

Speaker: Baptiste Rousset, UC Berkeley

Title: Searching for slow slip events hidden in the noise of GPS and InSAR time series

October 20, 2017

Speaker: Alicia Hotovec-Ellis, USGS

Title: Slips, Screams, and Migrating Things: Repeating earthquakes as a toolbox to understand and monitor volcanoes

Abstract: Repeating earthquakes are a nearly ubiquitous feature of the seismicity at active and erupting volcanoes worldwide. A seismic source is persistently reactivated, producing nearly identical waveforms that can be identified and clustered by cross-correlation methods. Changes in the timing, location, and waveforms of these earthquakes can be informative about ongoing and evolving processes within a volcano. In this talk, I'll highlight several different examples of the utility of repeating earthquakes to understand a "screaming" volcano in Alaska, changes in the shallow velocity structure of Mount St. Helens, and swarms of deep migrating earthquakes under Mammoth Mountain.

October 27, 2017

Speaker: Gwanghyeok Ju, Director of the Lunar Exploration Research Division Korea Aerospace Research Institute (KARI)

Title: Korean Lunar Program Status

Abstract: KARI is developing the Korean Pathfinder Lunar Orbiter (KPLO) as part of Korean Lunar Exploration Program under the collaboration framework with NASA.

While KARI is leading KPLO project management and its design and implementation for the obiter spacecraft, other Korean institutions are working on different types of payloads in parallel. After the announcement of opportunity (AO) for the first Korean lunar mission was officially released by NASA HQ in September 2016, one NASA-side scientific instrument called ‘ShadowCam’ was added to four Korean scientific payloads, LUTI, KGRS, PolCam, KMAG, under development in late April 2017. It is known that ShadowCam will map the reflectance within the permanently shadowed regions to search for evidence of frost or ice deposits and observe the PSRs monthly to detect seasonal changes and measure the terrain inside the craters, including the distribution of boulders.

On the other hand, KARI is leading the pre-phase A study for 1st Korean lunar landing mission in parallel with the KPLO mission. KARI has led the lunar landing site working group with domestic scientists and engineers as part of preparatory activities for the lunar lander mission.

In this talk, an updated status of the KPLO is explained with respect to evolution in mission design, spacecraft design change, domestic & foreign instrument’s accommodation and so on.  The recent update of design status for Korean lunar science instruments is also presented in terms of specifications, preliminary design, pursuing lunar science, etc. In addition, the guidelines for landing site selection criteria are suggested for prospective Korean lunar landing mission. Potential landing sites can be analyzed with respect to resource-bearing, scientific impact, demonstration of accurate landing capability, etc.

November 3, 2017

Speaker: Asaf Inbal, UC Berkeley

Title: Sources of deep episodic slip and the weak seismic wavefield near Anza, CA  

November 17, 2017

Speaker: Jerome Neufeld, Cambridge University

Title: Fluid deformation of the solid Earth: Bending and breaking rock and ice

Abstract: The propagation of magma forming dykes and sills, and the drainage of supraglacial lakes are examples of fluid-driven surface deformation.  An understanding of these processes relies crucially on the coupling of fluids and elastic solids.  This talk will explore the buildup and drainage of supraglacial lakes along the margins of the Greenland ice sheet, and their role in the transient and long-term lubrication of the Greenland ice sheet, and the fracturing of rock during the emplacement of sills and laccoliths.  Drawing on laboratory experiments and field data, it will show the crucial role that physical processes at the fracture front play in the emplacement of geological fluids in these different settings.

December 1, 2017

Speaker:  Thomas Kruijer, LLNL

Title: Timescales of Jupiter’s growth inferred from isotopic analyses of meteorites

December 8, 2017

Speaker: Nana Yoshimitsu, Stanford

Title:  Toward the robust stress drop estimates for induced earthquakes in Oklahoma

Abstract: Stress drop is important factor for a better understanding of ground motion intensity. Precise estimation of the stress drop is important to understand the behavior for induced seismicity; however, published estimates of stress drop are both strongly variable and subject to large uncertainties. In this study, we focus on assessing the fit to the data across the measurable frequency range to understand the trade-offs among the parameters of the theoretical model.

We gathered co-located events within 1 km from large (Mw >= 4) events in Oklahoma, using relocated highly accurate event list from May 2013 to November 2016 (Schoenball and Ellsworth, 2017). We formed spectral ratios of S wave (5.12 seconds) at 100 sps waveforms, between a large and eGfs event pair by stacking all available stations. The best model was estimated using least square grid search by fitting Brune spectral model to the data over a frequency range of 1 to 40 Hz. We evaluated the trade-off among three unknown parameters, two corner frequencies and the moment ratio, from the confidence intervals obtained during the 1000 times bootstrap trials. We discarded event pairs with a large trade-off between any of two parameters. In addition, we assessed the distribution of the residual and the slope of the residual.

After assessing the suitability of the eGf with above procedures, the spectral ratios which have irregular shapes were ignored. Standard deviation of the estimated stress drops of large earthquake reduced in all clusters. Considering these results, we conclude that event selection using trade-off, residual distribution, and residual slope increases stress drop estimation accuracy.