Spring 2017

April 7, 2017

Speaker: Zack Spica, Stanford

Title: The power of higher-order cross-correlations (C3) to image the Earth from the crust to the core

Abstract: The ambient noise correlation technique allows retrieving the Green's function between pairs of synchronous seismic sensors by correlating long time series of seismic noise (C1). While the method is widely used to map the seismic velocity in the crust and upper mantle with surface waves, recent works highlighted the possibility to retrieve teleseismic body waves, offering a better sampling geometries to image the Earth's core. However, the method relies on the availability of synchronous networks, which considerably limits the ray-paths coverage and therefore the resolution of the resulting tomographic images.  
My point is to show that performing higher-order correlations (C3) makes it possible to bridge all the seismic networks in time and space, and therefore significantly enhance the resolving power of the ambient noise tomographies. I will discuss the feasibility and the potential of the method for Rayleigh waves retrieval, and present its first application to obtain a high-resolution tomographic image of Mexico and south US. In addition, I will show that the method can also be extended to retrieve teleseismic body waves such as reflections on the core mantle boundary. I will present a spatial analysis of the differential travel time of the ScS phase along the Meso America Subduction Experiment (MASE) array and discuss the strong influence of the shallow surface on such measurements.

April 14, 2017

Speaker: Thomas Bristow, NASA Ames

Title: Exploration of Ancient Habitable Environments on Mars

April 21, 2017

Speaker: Tobias Keller, Stanford

Title: Modelling magma transport from source to surface

April 28, 2017

Speaker: Peter Gao, NASA Ames

Title: Cloud Physics in the Age of Exoplanets (and Brown Dwarfs)

May 5, 2017

Speaker: Johanna Nevitt, USGS

Title: Impacts of compliant zones and elastoplasticity on the mechanics of near-surface faulting

May 12, 2017

Speaker: Leif Karlstrom, University of Oregon

Title: Long-term controls on short-term patterns of magmatism, from crustal thickening to volcanic eruption cycles

May 19, 2017

Speaker: Jörn Davidsen, University of Calgary

Title: From rock fracture in the lab to induced seismicity and aftershocks

May 26, 2017

Speaker: Katherine Kretke, Southwest Research Institute

Title: From Pebbles to Planets

Abstract: In recent years there has been a radical shift in the thinking about small-body and planet formation.  Particles with stopping times comparable to their orbital times, often called "pebbles" (although they may range from sub-centimeter to almost meters in size), interact with gaseous protoplanetary disks in very special ways.  This allows them to not only directly produce the planetesimal building blocks of planetary systems, but also later to accrete on to these planetesimals, potentially solving long standing mysteries about the Solar System's formation: the low mass and mixed composition of the asteroid belt, Mars's small size, and the very existence of Jupiter and Saturn.  In this talk I will review these recent developments and discuss the promises of using pebbles to solve many problems in the formation of our own, and other, planetary systems.

June 2, 2017

Speaker: Luca Malatesta, UCSC

Title: Formation of waterfalls by intermittent burial of active faults

Abstract: Waterfalls commonly exist near bounding faults of mountain ranges, where erosional bedrock catchments transition to depositional alluvial fans. We hypothesize that aggradation on alluvial fans can bury active faults, and that the faults accumulate slip in the subsurface to produce a bedrock scarp. Following entrenchment of the alluvial fan, the scarp can be exposed as a waterfall. To explore this hypothesis, we derive a geometric model for waterfall height which depends on alluvial fan length and the relative timescales of 1) tectonic uplift, 2) a forcing for cycles of fan aggradation and entrenchment, and 3) a response of fan aggradation to changes in sediment flux. We find that the model is consistent with observations at Gower Gulch, Death Valley, CA, where a man-made drainage capture event in 1941 caused rapid fan incision and exposed a waterfall at the canyon-fan transition. We also compare the model to 62 waterfalls in 18 catchments of the Death Valley area, and find that at least 15 of the waterfalls are best explained by the fault burial mechanism. Using field measurements of grainsize and channel geometries, we show that the fault-burial mechanism can produce the observed waterfall heights, measuring 4 to 19 m, under a uniform climatic forcing requiring variations of 20% in precipitation during the Late Pleistocene. The fault burial mechanism, through the creation of upstream propagating waterfalls, may allow catchment-fan systems to experience frequent cycles of enhanced erosion in catchments and deposition on fans, that likely convolve tectonic and climatic signals.

June 9, 2017

Speaker: Greg Stock, Yosemite Park

Title: Measuring glacier loss in Yosemite National Park

June 16, 2017

Speaker: Jean-Arthur Olive, Lamont

Title: Controls on the seafloor exposure of detachment fault surfaces