Fall 2015

September 18, 2015

Speaker: Rebecca Fischer, Smithsonian Institute

Title: Earth's accretion, core formation, and core composition

September 25, 2015

Speaker: Megan Bruck Syal, LLNL

Title: Asteroid and comet impacts: planetary defense at Earth and water delivery at Mercury and the Moon

October 2, 2015

Speaker: Zachary Ross, USC

Title: Applying automatic techniques to large seismic datasets for comprehensive studies of regional and fault zone environments

Abstract: The amount of recorded seismic data is rapidly increasing and it is often unfeasible to manually perform basic tasks such as earthquake detection and location. The development of robust, automated techniques for handling these types of tasks, however, has significantly lagged behind the rate of data acquisition. We discuss a collection of algorithms for earthquake detection, real-time P- and S-wave arrival picking, and fault zone head and trapped wave identification for local earthquakes in fault zone environments. We show that together, these techniques are capable of producing self-consistent databases in automatic fashion with a level of quality rivaling that of a permanent seismic network. The algorithms are applied systematically to large seismic datasets recorded in the San Jacinto fault zone, Parkfield, and Taiwan, which span months to years. We demonstrate significantly enhanced detection rates and location accuracies, and objectively quantify uncertainties against arrival picks made by permanent network analysts. The resulting databases are used to perform high-resolution imaging of fault zone structures, study regional tectonics, and measure crustal shear-wave anisotropy.


October 9, 2015

Speaker: Julian Lozos, USGS

Title: A Case for Historic Joint Rupture of the San Andreas and San Jacinto Faults

October 16, 2015

Speaker: Rob DeRosa, UC Berkeley

Title: The Gemini Planet Imager Exoplanet Survey

Abstract: Measuring the frequency and distribution of extrasolar planetary systems provides crucial context to understand the formation of our own Solar System. While ongoing radial velocity and transit surveys are beginning to have sensitivity to terrestrial planets at separations similar to those within our own Solar Systems, wider Jovian-mass planets remain out of reach. Direct imaging provides a complementary detection technique, being sensitive to the thermal emission from young gas giants in wide (>10 AU) orbits around nearby (<100 pc) stars. Using a high-order adaptive optics system, an apodized pupil coronagraph, and an integral field spectrograph, the recently commissioned Gemini Planet Imager (GPI) was designed to directly image such planetary systems. Our team is currently undertaking an 890-hour campaign — the Gemini Planet Imager Exoplanet Survey (GPIES) — to search for planetary-mass companions in wide orbits (4-40 AU) around a sample of 600 nearby, young (<300 Myrs) stars. I will discuss the current status of the survey, which began in late 2014, and highlight several of the early science results, most notably the discovery of the cool exoplanet 51 Eridani b.


October 23, 2015

Speaker: Cedric Twardzik, UCSB

Title: Constraining the physical parameters of source dynamics by inversion of seismic waveforms

October 30, 2015

Speaker: Jeremy Tregloan-Reed, NASA Ames Research Center

Title: Oxidation of Earth-like Exoplanets through Weathering – Through a Purely Abiotic Process

November 6, 2015

Speaker: Tom Parsons, USGS

Title: Earthquake rupture process in model fault zones

November 13, 2015

Speaker: Mark McClure from UT-Austin

Title: Applying Bayes' theory to assess statistical significance of potentially induced seismicity due to wastewater injection in Oklahoma and California

November 20, 2015

Speaker: Aomawa Shields, UCLA/Harvard

Title: Exoplanet Climatology: The Next Era of Habitable-planet Hunting

Abstract: The identification of an exoplanet receiving the amount of incident
radiation from its host star to lie within the star’s habitable zone has
been the primary step taken in classifying a planet as "potentially
habitable". However, recent research and the history of our own planet have
shown that many factors and processes can affect climate and planetary
habitability. Discovering a planet in the habitable or "Goldilocks" zone is therefore
but a first step in the process of finding the next planet where life can
survive. To identify habitable worlds beyond our solar system, it is important to
understand how both orbital and atmospheric properties affect the climate
of exoplanets, and how these climatic effects might change for different
stellar and planetary environments. I will share results from work performed using a
hierarchy of models to simulate planets orbiting stars of different spectral types
and with varied orbital architectures, and discuss the implications of
these results for planetary climate and habitability. My methods will help
assess the possible climates of potentially habitable planets as they are
discovered. This work ushers in a new era of utilizing observational data
and theoretical techniques together to target the next planet where life
exists.


November 27, 2015

THANKSGIVING BREAK



December 4, 2014

Speaker: Martin Schoenball, USGS

Title: Differentiating Induced and Natural Seismicity Using Space-Time-Magnitude Statistics Applied to the Coso Geothermal Field

Abstract: A remarkable characteristic of earthquakes is their clustering in time
and space, displaying their self-similarity. It remains to be tested
if natural and induced earthquakes share the same behavior. The Coso
Geothermal Field is one of the most seismically active areas in
California and features an abundance of natural seismicity due to
active tectonics and a large number of induced earthquakes resulting
from geothermal power production since 1987. We study natural and
induced earthquakes comparatively in the same tectonic setting at the
Coso Geothermal Field. Covering the pre- and co-production periods
from 1981 to 2013, we analyze inter-event times, spatial dimension,
and frequency-size distributions for natural and induced earthquakes.
Individually, these distributions are statistically indistinguishable

Determining the distribution of nearest-neighbor distances in a
combined space-time-magnitude metric lets us identify the triggering
relationship of an earthquake pair. Nearest-neighbor pairs naturally
fall into two populations that are categorized as either clustered
(triggered) or background (independent) events.

At Coso, induced earthquakes feature a larger fraction of background
seismicity compared to natural earthquakes. Furthermore, they contain
a population of independent pairs at large magnitude-rescaled times
and small magnitude-rescaled distances. This implies that unlike
tectonic processes, stress changes induced by the field operations
occur on much smaller time scales and appear to be large enough to
drive small-scale faults through several seismic cycles during
relatively short observation period. As a result, we record events
close to previous hypocenters that occur up to a year after the
preceding earthquake.


December 11, 2014

Speaker: Seth Jacobson, Obs. Cote d'Azur

Title: The last giant impact on Earth