Winter 2017

January 13, 2017

Speaker: Chris Rollins, Caltech

Title: Strain accumulation on faults beneath Los Angeles: a geodesy-based picture accounting for the effects of sedimentary basins and anthropogenic surface deformation

Abstract: The Big Bend of the San Andreas leaves a component of ~8 mm/yr of north-south contraction across the Los Angeles region to be accommodated by slip on thrust systems such as the Sierra Madre,
Puente Hills and Compton faults. A large earthquake on one of these systems could constitute a worst-case-scenario event for Los Angeles, and so it is essential to use geodetic data to constrain where, and
how quickly, tectonic strain is accumulating on these faults. Using the refined GPS velocity field of Argus et al [2005] and detailed models both of 3D fault geometries and of elastic structure (based
respectively on the SCEC CFM5 and CVM-H15.1), we show that: 1) The Los Angeles sedimentary basin has a first-order effect on the problem; more coupling at depth is required to fit a given contractional
gradient with the basin than without, increasing the inferred buildup rate of seismic moment by over 50%. 2) Deep creep on strike-slip faults at their geologic slip rates can produce an apparent N-S
contractional gradient of ~1.5 mm/yr across the LA region. 3) The contractional gradient in GPS is well fit by models featuring slip rates of ~5 mm/yr on the Sierra Madre Fault, ~3.5 mm/yr each on the
Puente Hills and Compton faults, and a moment buildup rate of 2.4-3.4 x 1017 Nm/yr. This buildup rate requires a M=7 earthquake every 120-160 years if released in a characteristic M=7 earthquake, but this
does not account for seismicity at other magnitudes. Using the SCEDC and relocated Hauksson et al. [2011] catalogs, we find that the slip budget can be balanced by a Gutenberg-Richter distribution of
earthquakes and the aftershocks of those earthquakes with maximum-magnitude M=7.2-7.4 earthquakes every 900-1300 years.

January 20, 2017

Speaker: Wenyuan Fan, UCSD

Title: Earthquake interaction and triggering revealed by back-projection

January 27, 2017

Speaker: Thomas Göbel

Title: The 2016 Mw5.1 Fairview, Oklahoma earthquakes: Evidence for long-range poroelastic triggering at >40 km from fluid disposal wells

Abstract: Water disposal is likely responsible for an unprecedented surge in seismicity in the U.S. This activity is thought to be driven by induced pore pressure changes, which requires a direct hydraulic connection between faults and wells. However, direct pressure effects are questionable for earthquakes located at large distances from the injectors. We examine triggering mechanisms of induced earthquakes, which occurred at more than 40 km from disposal wells in northwest OK. Our results indicate that poroelastic stresses can play a significant role in triggering earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir.

February 17, 2017

Speaker: Amy Dale, MIT

Title: Integrated multi-scale simulation to support water quality decision-making

Abstract: Population growth, land use change, and climate change place a tremendous burden on the world’s waterways.  Urbanization and agricultural intensification increase surface water loads of nutrients, sediments, and pathogens.  Climate change alters the timing and magnitude of pollutant loads and increases water temperatures.  Water quality degradation threatens human and environmental health and also threatens food and energy production due to the water demands of (e.g.) irrigation, hydropower, and thermoelectric power plant cooling.  Decisions that help mitigate these impacts must be made at all scales, from local to global.  This talk will summarize my current efforts and future research plans in the area of integrated numerical simulation to improve water quality assessment and inform decision-making at multiple scales.  My current research concerns the development of a continent-scale model that predicts the future impacts of climate change on maize production and irrigation water supply and demand across sub-Saharan Africa.  My future research will focus on (1) model design to better assess the environmental fate of particulate and strongly sediment-associating contaminants such as sediments, waterborne pathogens, harmful algal blooms, and metals, and (2) integrated environmental modeling to better inform water quality policy development, investment planning, and risk management in the face of global change.

February 24, 2017

Speaker: Mathis Hain, University of Southhampton

Title: Reconstructing the geologic backdrop to ocean acidification

Abstract: Ocean uptake of anthropogenic CO2 is associated with progressive reductions in seawater pH, carbonate ion concentration and calcium carbonate saturation state; a set of changes that is collectively referred to as Ocean Acidification, OA. Based on a growing body of field observations and controlled experiments there is concern that OA is a significant environmental stressor on marine life, and in particular on organisms that build carbonate skeletons. And yet, beyond the immediate effects of OA we know little about the resilience that marine organisms may have evolved from natural changes in seawater acid/base chemistry during geologic time and the range of environmental conditions marine organisms may therefor be able to adapt to as OA proceeds into the future. Here I describe some of my recent work aimed at understanding the chemical principles that govern seawater acid/base and carbonate chemistry on geologic timescales. This work also includes the development of a computational framework to combine the boron isotope pH proxy, reconstructions of seawater major ion composition and records of carbonate burial in deep sea sediments to reconstruct seawater pH, carbon concentration and carbonate saturation as well as atmospheric CO2 back through time. These records offer invaluable information on the limits of resilience of marine life to future OA.

March 3, 2017

Speaker: Matthew Winnick, Stanford

Title: Quantifying Terrestrial Moisture Recycling Dynamics from Lateral Gradients of Isotopes in Precipitation

Abstract: Averaged across the globe, roughly 40% of precipitation that falls on land has been recycled through terrestrial evapotranspiration processes. This recycling of water through terrestrial systems is an integral part of the hydrologic cycle, and constraining the response of recycling dynamics with changing climate is of vital importance for predicting future change. In this talk, I will present a quantitative framework for constraining atmospheric transport dynamics and evapotranspiration rates from synoptic-scale lateral gradients of isotopes (δ18O, δD, deuterium-excess) in precipitation. This framework will be extended to address the monitoring of changes in moisture recycling rates and the partitioning of recycling between plant transpiration and soil evaporation with future climate change, as well as the reconstruction of terrestrial hydrologic change in past climates through the use of paleoclimate proxy records.

March 10, 2017


Speaker: Sam Johnson, USGS - Santa Cruz

Title: Neotectonics of the Hosgri-San Gregorio fault system

March 17, 2016

Speaker: Margaret Zimmer, Duke

Title: Pushing the boundaries of watershed science through coupled hydrologic observations and models

Abstract: Water quality and quantity are complex issues that span local to global scales. There are still significant gaps in our understanding about the stores, fluxes, and chemical signatures of the major components of the hydrologic cycle. As a watershed hydrologist, I plan to 1) continue to improve discipline-specific frameworks in the hydrologic sciences, 2) target research toward understanding human-induced change on hydrologic systems, and 3) provide a process-based understanding that can be used toward sustainable management of hydrologic systems. I will utilize new data observations, models, and frameworks to address these three main short term career goals. For this talk, I will introduce active research addressing these topics as well as my future research I plan to conduct in my first years as an assistant professor.