School of Earth and Environment

Jessica Hawthorne Dr Jessica Hawthorne

Academic Research Fellow

Email address: J.C.Hawthorne@leeds.ac.uk
Room: 9.158

Affiliation: Institute of Geophysics and Tectonics

Biography

I am a permanent-track academic research fellow in geophysics at the University of Leeds. In my research, I investigate the mechanics of slip on faults. We want to understand why some faults slip at a steady rate near plate rate, others slip in large earthquakes, and still other faults slip in a series of slow earthquakes. And we want to understand how these processes work. For instance, how does an earthquake nucleate and grow, and what physical processes stop some faults from accelerating to seismogenic speeds?

Large populations around the world live near faults that host large and small earthquakes. As we improve our understanding of seismic and aseismic slip, we seek to incorporate more physical modeling into estimating and mitigating seismic hazard, so that we can better interpret what has happened on faults in the past in terms of what might happen in the future.

I use three primary tools in investigating earthquakes and seismic slip on faults: seismology, geodesy, and frictional modeling. Much of my work focuses on finding the most effective ways to test models of fault slip with laboratory results and geophysical observations. We are always trying to organize the numerous seismic and geodetic data from small slip events in ways that can validate or disprove specific model hypotheses.

pdf of CV

Academic Research Fellow, University of Leeds, 2015 - present

Postdoctoral Fellow, California Institute of Technology, 2013-2014

Texaco Postdoctoral Fellow, California Institute of Technology, 2012-2013

Qualifications

Ph.D Geosciences, Princeton University, October 2012

M.A. Geosciences, Princeton University, May 2009

B.S. Earth Science, Rice University, May 2007

Research Interests

Recent Research Topics:

Observing and modeling short-timescale subevents within slow slip:

In slow slip events, or slow earthquakes, large parts of plate interface faults slip a few cm over the course of a few weeks to months. These slip speeds are six orders of magnitudes lower than slip speeds in normal earthquakes, which are limited by the generation of seismic waves. To help contribute to our understanding of why slow slip events are so slow, I observe and model some of the subdaily variations in slow slip events. Most recently, I have been examining the stress drops in several-hour-long tremor reversals, which appear to be lower than the main event stress drops even though the reversals propagate more quickly (paper below). With Abhijit Ghosh (U. Riverside) I have also been examining slip before and after the 30-second-long very low frequency earthquakes in Cascadia.

In order to observe these short-timescale variations in aseismic slip, I use the high-precision PBO borehole strainmeters, capable of recording sub-nanostrain (1 mm offset over 1000 km) deformation. Some new approaches for reducing the noise in these data are described in the paper below.

Hawthorne JC; Bostock MG; Royer AA; Thomas AM (2016) Variations in slow slip moment rate associated with rapid tremor reversals in Cascadia, Geochemistry, Geophysics, Geosystems, . doi: 10.1002/2016GC006489

Estimating the spatial extent of small earthquakes and tremor:

I have been developing a technique to estimate the spatial extent of small earthuakes based on the relative timing of energy coming from different locations within the rupture. Currently grad student Josh Williams is using this method to examine time-varying stress drops in earthquakes on the Blanco Transform Fault. With Amanda Thomas (U. Oregon), I am using this approach to examine the potentially unusual rupture dynamics of low frequency earthquakes that constitute tremor. Our results imply that the spatial extent of low frequency earthquakes is at least a factor 4 smaller than would be expected if the events ruptured at a speed of 80% of the shear wave speed, as is typical for normal earthquakes.

EGU presentation about the method: https://www.dropbox.com/s/ncu3rtdqqsk9eva/presentation.pdf?dl=0

AGU presentation about the rupture extent of low frequency earthquakes in tremor: https://www.dropbox.com/s/d5jh7x6kw3t3m1o/presentation.pdf?dl=0

Phase coherence analysis for identifying and locating tremor using earthquakes as templates:

With former postdoc supervisor Pablo Ampuero, I have developed a technique to detect and locate closely spaced seismic signals, even if those signals have complex source time functions. The approach is especially useful for identifying signals that are close in space but different in nature---like an earthquake and tremor, or two earthquakes of different sizes. I have used this method to examine a 20-second-long tremor-like precursor to a M 3.9 earthquake in central Alaska, identified by Tape et al, 2013, and to examine volcanic tremor at Redoubt Volcano composed of repeating earthquakes, also discussed by Hotovec et al, 2013. Details of the method and applications are described in the manuscript below. Python codes are available on request, but only if you're willing to work through some bugs.

Publications

J. C. Hawthorne, and J.-P. Ampuero. A phase coherence approach to identifying co-located earthquakes and tremor. Geophys. J. Intl. (Accepted, available at https://www.dropbox.com/s/b4caastyje3gbdy/phase-coherence-tremor.pdf?dl=0.)

J. C. Hawthorne, J.-P. Ampuero, and M. Simons. A method for calibration of local magnitude scale based
on relative spectral amplitudes, and application to the San Juan Bautista, CA area. Bull. Seis.
Soc. Amer., published online 2016, available at
https://www.dropbox.com/s/cahmk33vm4se2r5/SJB-magnitude-calibration.pdf ?dl=0.

Publications