John Elliott is a postdoctoral scientist at the University of Oxford. He works on modelling earthquakes using deformation data, and is co-funded by COMET and the Earthquakes without Frontiers consortium.
Understanding the August 2014 Napa Valley earthquake
For more than two decades, space-based radar satellites have been measuring how the ground moves with extraordinary precision and spatial resolution. Comparing ground heights from the same places at different times helps scientists to understand the dynamics of a variety of geophysical events including earthquakes.
On 24 August 2014, the San Francisco Bay area was shaken by a Mw = 6.0 earthquake, the region’s largest in 25 years. The tremors killed 1 person, injured around 200 and damaged buildings near the quake’s epicentre in the southern reaches of California’s Napa Valley.
It also set off a scientific scramble to measure the fault’s movement, and marked the dawn of a new age of earthquake monitoring thanks to the recent launch of Sentinel-1A.
By combining satellite data with GPS measurements made by our US colleagues on the ground, we were able to show that motion on the fault continued to slip in the weeks following the earthquake in a process called postseismic afterslip.
Using these regularly repeating observations, we found a whole range of different fault slip behaviour on the fault plane: from rapid shallow slip to slower, more prolonged, deeper slip.
Observations such as these are important for constraining types of fault slip behaviour and as a starting point to begin to understand the fault frictional behaviour. This variability should be incorporated into seismic hazard models.
The research received extensive media coverage, including by the BBC:
Sentinel system pictures Napa quake
Sentinel radar satellite tracks continued Napa slip after quake
Floyd, M., Walters, R.J., Elliott, J.R., Funning, G., Svarc, J., Murray, J., Hooper, A., Larsen, Y., Marinkovic, P., Burgmann, R., Johanson., I., Wright, T.J. (in prep.) Afterslip evolution following the 2014 South Napa earthquake exposes variations in fault plane friction.
Elliott, J. R., Elliott, A., Hooper, A., Larsen, Y., Marinkovic, Wright, T.J. (2015) Earthquake Monitoring Gets Boost from a New Satellite, EOS 96. doi:10.1029/2015EO023967