Fall 2019

Fridays at 12:00 PM

E&MS A340

September 27, 2019

Speaker: Ariel Lellouch, Stanford

Title: Seismic velocity estimation and earthquake detection using downhole optical fiber sensing (DAS) - examples from SAFOD


October 4, 2019

Speaker: Nicholas van der Elst, USGS

Title: Orphaned aftershocks and the duration of aftershock sequences

October 11, 2019

Speaker: Kathryn Steakley, NASA Ames Research Center

Title: Testing the Impact Hypothesis for Warming Early Mars


October 18, 2019

Speaker: Diogo Lourenço, UC Davis

Title: The influence of melting and viscosity on the thermo-chemical evolution of Earth and other rocky planets


Abstract: In this presentation I will firstly show results from numerical simulations of global mantle convection to explore the effects of melting on the thermo-chemical evolution of terrestrial bodies. I applied the models to investigate (i) how does melting-induced crustal production affects the interior state and surface behavior of an Earth-like planet, and (ii) the effects of intrusive versus extrusive magmatism on the surface tectonics and mantle cooling of a terrestrial planet. Results show that (i) melting-induced crustal production helps plate tectonics on Earth-like planets by strongly enhancing the mobility of the lid; (ii) high intrusion efficiencies (i.e. dominance of intrusion versus extrusion) lead to a new tectonic regime, named “plutonic-squishy lid” characterized by a set of strong plates separated by warm and weak regions generated by plutonism, and can cool the mantle more efficiently than volcanic eruptions for planets with no subduction in their history.
In the second part of the talk I will focus on the present-day structure and dynamics of the Earth. Seismic images of Earth’s mantle have revealed changes in mantle structure between 400-1000 km depth. The structures at these depths appear to be different in nature from the lowermost mantle or the lithosphere. I demonstrate that the changes in structure are driven primarily by the reduced rate of sinking of subducted oceanic plate material in the western Pacific basin. Next, I use numerical models of mantle convection to demonstrate that the observed structures can be best explained by a relatively large increase in mantle viscosity between the upper mantle and lower mantle at 660 km depth or perhaps somewhat deeper, near 1000 km.

October 25, 2019

Speaker: Matija Ćuk, SETI Institute

Title: Early Dynamics of the Moon's Core


November 1, 2019

Speaker: Michael Oskin, UC Davis

Title: Earthquake Gates of the Altyn Tagh Fault: Linking Rupture Length to Geologically Constrained Dynamics of Fault Complexity

November 8, 2019

Speaker: Heda Agic, UCSB

Title: Fossils and paleoecology of Earth's earliest complex life


November 15, 2019

Speaker: Elizabeth Cochran, USGS

Title: Evolution of induced earthquake sequences in response to local wastewater disposal in southern Kansas


November 22, 2019

Speaker: Thorne Lay, UCSC

Title: The December 22, 2018 Krakatau Eruption-Landslide-Tsunami: How Could Early Warning Have Been Given

December 6, 2019

Speaker: Behrooz Ferdowsi, Princeton

Title: A granular-physics-based view of fault friction experiments

Abstract: Rate- and State-dependent Friction (RSF) equations are commonly used to describe the time-dependent frictional response of fault gouge to perturbations in sliding velocity. Among the better-known versions are the Aging and Slip laws for the evolution of state. Although the Slip law is more successful, neither can predict all the robust features of lab data. RSF laws are also empirical, and their micromechanical origin is a matter of much debate. Here we use a granular-physics-based model to explore the extent to which RSF behavior, as observed in rock and gouge friction experiments, can be explained by the response of a granular gouge layer with time-independent properties at the contact scale. We examine slip histories for which abundant lab data are available, and find that the granular model (1) mimics the Slip law for those loading protocols where the Slip law accurately models laboratory data (velocity-step and slide-hold tests), and (2) deviates from the Slip law under conditions where the Slip law fails to match laboratory data (the reslide portions of slide-hold-slide tests), in the proper sense to better match those data. The simulations also indicate that state is sometimes decoupled from rock gouge porosity in a way that is inconsistent with traditional interpretations of` “state” in RSF. Finally, if the “granular temperature” of the gouge is suitably normalized by the confining pressure, it produces an estimate of the direct velocity effect (the RSF parameter a) that is consistent with our simulations, and in the ballpark of lab data.