EMILY BRODSKY Associate Professor of Earth & Planetary Sciences Earthquakes, volcanoes, fluid flow in fractured media
		Office: EMS C370 Phone: 831-459-1854 Fax: 831-459-3074 E-mail: ebrodsky@es.ucsc.edu Lab: C366 x9-5263		For more information: • Website

Education and Training

B.A. Magna cum laude, Harvard University
Ph.D., California Institute of Technology

Research Interests

I am studying the physics of earthquake and volcanic eruptions by using fluid dynamics to formulate new interpretations of seismic and other geophysical data. My research falls into three general areas: earthquake triggering, friction, and co-eruptive seismic studies.

Triggering Earthquakes

Why do earthquakes happen? At one level, this age-old question was solved by the plate tectonics revolution in the 1960's. It was found that earthquakes accommodate motion as large, nearly rigid plates slide past each other. Yet, this broad explanation for slip leaves many of the key questions unanswered. Why is slip sometimes accommodated by gradual creeping and at other times by rapid failure? Why do some earthquakes stop after only a few meters of rupture while others continue for 1000 km? How do earthquakes interact? Most importantly, what is the trigger for slip?

Friction

Since friction is the major resisting force during an earthquake, it is the key to understanding how earthquakes grow, how large waves they generate and how big they are going to be. We are currently measuring fault roughness in the field and also doing laboratory experiments on rocks to try and establish what dynamical regime best describes the friction of rocks during earthquakes. Mechanisms like hydrodynamic lubrication (Brodsky and Kanamori, 2001) may help to explain low friction on faults during rupture.

Seismic records of landslides also provide insight into natural friction processes. A landslide generates seismic waves by both shearing and loading the surface as the mass moves from a steep to a shallow slope. The effective force system is a horizontal single force. The amplitude of the seismic waves is proportional to the force drop during the landslide, just as during an earthquake the seismic wave amplitude is proportional to the seismic moment, i.e., the force drop multiplied by the source dimension. For landslides we know an additional variable that is unknown for the earthquake case. We know the gravitational driving force of the landslide while the magnitude of the tectonic forces that drive earthquakes are generally unknown. Therefore, we can find the absolute value of the frictional force for landslides whereas we are unable to perform this calculation for earthquakes. In Brodsky et al. 2003, we found that three large volcanic landslides were all consistent with an apparent coefficient of friction of 0.2.

Co-eruptive seimic data

In the past I have measured the mass ejection rates of explosive eruptions from the seismic waves and, more recently, constrained the basal friction of volcanic landslides (Brodsky et al., 1999; Brodsky et al., 2003) . In the future, we plan to use modern match-filter techniques to extract seismicity from notoriously messy co-eruptive seismograms. No one has ever been able to see earthquakes during an eruption before. If we succeed in extracting these events, we will have a new, fundamental constraint on the brittle processes during eruptions. I hope to use this tool to examine conduit growth and subsequent failure, which are two of the most important (and most poorly constrained) processes that determine the course of an eruption.

Teaching Interests

Earthquakes (EART 80B)