Spring 2020

Fridays at 12:00 PM


April 3, 2020

Speaker: Vashan Wright, UC Berkeley and WHOI

Title: New Insights into the Neotectonics of the Enriquillo-Plantain Garden Fault Zone and the Resistance of Sands to Earthquake-Triggered Deformation: The Science Behind Jamaica’s Under-Recognized Hazard

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Abstract: Fault activity and sediment strength characterizations are crucial for hazard assessment in diffuse continental strike-slip boundaries like the Enriquillo-Plantain Garden Fault Zone (EPGFZ). This left-lateral fault zone extends through Eastern Jamaica and Western Hispaniola, and has generated at least one large magnitude (> Mw 6) earthquake per century (e.g., the Mw 7 2010 Haiti earthquake) over the last five centuries. The three most recent significant earthquakes resulted in tsunamis, landslides, and ground fissures that exacerbated damage levels. In this talk, I provide new insights into the neotectonics (i.e., recent tectonics) of the EPGFZ in Jamaica and demonstrate that the age of sands is a critical factor controlling their resistance to earthquake-triggered geohazards. I will first argue that, contrary to previous interpretations, the EPGFZ extends into Kingston, the capital city of Jamaica, where two-thirds of the population (1.2 million people) lives. Evidence for my interpretation derives from marine seismic-reflection profiles and sediment cores, showing that one of the prominent strike-slip faults within the EPGFZ extends into the Harbor offshore Kingston and is currently deforming a latest-Pleistocene extensional basin. This newly identified fault system represents significant hazards to Kingston because the faults are active and could generate a magnitude 4.7-6.7 earthquake. Moreover, ground motions from a >Mw 5.2 earthquake are expected to trigger liquefaction and slope failures within Kingston, particularly along the Port Royal Beach, where there have been three cases of liquefaction within this century. Sidewall coring, seismic velocity, and rock physics modeling analyses indicate that sands within the upper 2 m of this beach experience an increase to their elastic moduli with time since deposition. These time-dependent elastic moduli increases occur due to microstructural grain re-adjustments (e.g., grain rotation and slippage) that are unaccompanied by statistically significant time-dependent changes to all measured compositional and bulk physical properties, including porosity and cementation. I argue that these observations represent the first coupled field and theoretical-based evidence for a newly discovered process within the sedimentary lithification process. My results, therefore, contradict long-standing predictions that mechanical compaction is the dominant process influencing the shear strength, porosity, microstructural fabric, and liquefaction resistance of relatively recently deposited (i.e., within the first 180 years) shallow sands.


April 10, 2020

Speaker: Yann Klinger, Institut de Physique du Globe

Title: What earthquake surface ruptures teach us about earthquake processes and fault geometry

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April 17, 2020

Speaker: Leigh Anne Reidman, UCSB

Title: Vase-shaped Microfossils and Apatitic biomineralization in the late Neoproterozoic

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April 24, 2020

Speaker: Joe O'Rourke, Arizona State University

Title: The Interior Structure and Dynamics of Venus

Abstract: Venus is often called Earth's evil twin. However, whether Venus was clement in the past is debated. Here I will discuss two major features that would illuminate the accretion and evolution of Venus. First, a thick basal magma ocean may exist today. Second, crustal remanent magnetism may await detection almost anywhere on the surface. These glaring unknowns highlight the pressing need to further explore Venus.


May 1, 2020

Speaker: Jason Barnes, University of Idaho

Title: NASA's Titan Rotorcraft Lander

Abstract: Dragonfly is NASA's most recently selected planetary mission. Its science is prebiotic chemistry, habitability, and a search for chemical biosignatures on Saturn's huge moon Titan. Titan's draw derives from its status as an Ocean World. Like Europa, Enceladus, and potentially other icy outer solar system objects, Titan sports a liquid water ocean beneath its icy outer crust. But unlike those sister Ocean Worlds, Titan's surface and atmosphere contain a large quantity and complexity of carbon compounds. When liquid water develops transiently on Titan's surface -- either from cryovolcanism or impact melt -- water mixes with that surface organic material. Dragonfly will explore the chemistry of the resulting mixture at 80-km-diameter Selk Crater where that water, though now frozen, shows pathways for prebiotic chemistry that may resemble the process through which life formed on Earth 4 billion years ago. In my colloquium, I will discuss the specific scientific experiments that the Dragonfly lander will enable, as well as the instrumentation and exploration strategies that the science team will use to answer our science questions once we land in 2034.


May 8, 2020

Speaker: Lars Hansen, University of Minnesota

Title: When rocks push back: Residual stresses in mantle rocks and their role in geodynamics

Abstract: Deformation of Earth's upper mantle controls a wide variety of geodynamic processes, including the buildup of stresses on seismogenic faults, the formation of new plate boundaries, and the uplift of the lithosphere after removal of ice sheets. Most models of deformation of upper mantle rocks solely consider the long-term viscous behavior, in which the viscosity can be considered a constant. Here I investigate the shorter-term, transient behavior, in which the viscosity rapidy changes as deformation progresses. Experiments conducted at low temperature and high pressure in a D-DIA housed at the Advanved Photon Source reveal that deformation in this regime is controlled by the stresses from interaction of defects in the crystal lattices (dislocations). Complimentary experiments conducted at the University of Oxford, reveal that the same physical process of dislocation interaction is reponsible for the transient behavior at high temperatures (1300 C). Thus, a wide range of large-scale geodynamic processes effectively relies on the small-scale interactions of crystallographic defects.

lars


May 15, 2020

Speaker: Tamara Jeppson, USGS

Title: Understanding seismic velocity in fault zones


May 22, 2020

Speaker: Emily Brodsky, UCSC

Title: Earthquakes as a volumetric deformation phenomenon


May 29, 2020

Speaker: Chloe Beddingfield, SETI

Title: Polygonal impact craters on icy bodies


June 5, 2020

Speaker: Harsha Bhat, Laboratoire de Géologie, Ecole Normale Supérieure

Title: Earthquakes as a volumetric deformation phenomenon

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