Winter 2018

January 12, 2018

Speaker: Alexandre Schubnel, Ecole Normal Superior, Paris

Title: Rupture Processes During Laboratory Earthquakes

January 19, 2018

Speaker: Clara Yoon, Stanford

Title: Big data analytics for finding small earthquakes

January 26, 2018

Speaker: James Keane, Caltech

Title: The Wibbly Wobbly Moon: the Rotational Dynamics of the Moon Over Time

February 2, 2018

Speaker: Eduardo Bendek, NASA Ames

Title: Space Telescopes design for direct imaging and mass measurement of exoplanets

Abstract: Exoplanet detection and characterization of single and multiple planetary systems around nearby stars require different observational techniques. Performing simultaneous high-contrast imaging and astrometry observations of stars allows solving exoplanet orbits and masses faster and more precisely than using imaging or astrometry data separately. To perform both, direct imaging and astrometry observations of earth-like planets, a telescope utilizes a coronagraph capable of reaching 10-10 contrast, and a wide-field camera that can provide a sub-micro arc second astrometry. These instruments require optics that can deliver better than l/1000 wavefront accuracy using deformable mirrors, and cameras equipped with distortion stability calibration capability.  In this talk, we present the key optical design challenges of state-of-the-art exoplanet detection instrumentation exoplanet and challenges for future flagships missions such as HabEX and LUVOIR.

February 9, 2018

Speaker: Noel Bartlow, University of Missouri

Title: Insights into Slow Slip Events in Cascadia and New Zealand from a variety of geodetic data sources

February 16, 2018

Speaker: Tom Rockwell, San Diego State University

Title: Architectural Characteristics of Fault Zones in Southern California:
Physical Damage, Chemical Transformations and Implications for Dynamic Rupture

February 23, 2018

Speaker: Jessie Dotson, NASA Ames Research Center

Title: The NASA Ames Asteroid Threat Assessment Project

March 2, 2018

Speaker: William Frank, USC

Title: A multidisciplinary investigation of the slow grind of tectonic release

Absract: With the recent discovery of slow transient deformation at the roots of plate boundaries, there are many new fundamental questions about how these slow slip phenomena modify our understanding of how tectonic convergence is accommodated along plate interfaces. Geodetic data have been able to directly constrain the largest slow slip events, suggesting a slow rupture smooth in both time and space. On the other hand, seismology provides indirect observations of slow slip in the form of tectonic tremor and repeating low-frequency earthquakes that highlight a rough and intermittent evolution of slip on the plate interface. I will try to reconcile these contradictory observations by exploiting the time history of this slow seismicity to uncover new geodetic constraints that force us to reconsider the consensus model of slow deformation dynamics.

First, I will describe how GPS records between previously identified slow slip events do not represent continuous convergent motion and can in fact be decomposed into two distinct regimes of tectonic loading and release. This intermittent slip that was previously hidden within the noise demonstrates that the plate boundary where slow slip occurs can be as strongly coupled as the seismogenic zone and undergoes cyclic stress build-up and release over a wide range of time scales. I then investigate the short-period dynamics at the plate interface during a large slow slip event. I show that while the long-period surface displacements as recorded by GPS suggest a six month duration, motion in the direction of tectonic release only sporadically occurs over <60 days and its surface signature is attenuated by rapid relocking of the plate interface. These results demonstrate that our current conceptual model of slow and continuous rupture is outdated and is an artifact of low-resolution geodetic observations of a superposition of small, clustered slip events.

March 9, 2018

Speaker: David Goldsby, UPenn

Title: Experimental Constraints on the Ice Flow Law: Implications for Glaciers, Ice Sheets, and Icy Moons

March 16, 2018

Speaker: Thorne Lay, UCSC

Title: Resolving the up-dip extent of slip in large subduction zone earthquakes and its influence on aftershock distributions

Abstract: Slip distributions during large underthrusting earthquakes on subduction zone plate boundaries are now commonly determined using seismic, geodetic, and/or tsunami observations. A persistent challenge has been to constrain the up-dip extent of rupture, or how close to the trench coseismic sliding occurs. This issue is important for several reasons. Assessing the potential for shallow tsunami earthquakes that rupture the megathrust near the trench requires knowledge of whether prior deeper ruptures have extended to the trench. This is illustrated by the 2010 Mentawai tsunami earthquake, which ruptured up-dip of the 2007 Sumatra event. Earthquake slip at shallow depth also characterizes the frictional properties of the shallow megathrust and its seismogenic potential. On-land geodetic observations have little resolution of rupture if it occurs relatively far off-shore, as was demonstrated by analyses of the great 2011 Tohoku earthquake. Seismological observations alone also may have quite limited resolution of very shallow faulting on the up-dip portion of the megathrust. New approaches using water reverberations in the P coda hold promise of improving seismological resolution. Off-shore seafloor geodetic observations (GPS-Acoustic or ocean-bottom pressure sensors) significantly improve the determination of trenchward rupture extent, as shown for the 2011 Tohoku event, but only a few regions currently have sufficient instrumentation. For a number of recent large earthquakes, joint analysis of seismic and tsunami observations, in some cases including on-shore and off-shore geodetic data, appears to provide reliable estimates of up-dip slip extent (corroborated by direct imaging of seafloor offsets for 2010 Maule, Chile and 2011 Tohoku earthquakes). For the tsunami data to be best interpreted, corrections for path effects that have commonly been ignored must be included.