Lecturer: Nicolas Brantut (University College London)

Date: November 10, After the Unagi seminar

Place: DPRI Main Building E232D, Kyoto University Uji Campus

Title: Recovery of seismic wave speeds after deformation: A rock physics approach

Abstract:
In the upper crust, rocks deform by fracturing and faulting. Fractures and
microfractures have a huge impact on the physical properties of rocks, and
especially their seismic wave speeds. It is well established from
seismological evidences that important changes in seismic wave speeds occur
around fault zones in the periods following earthquakes: seismic wave
speeds tend to suddenly decrease during the earthquake, but tend to recover
significantly in the following days and months after rupture. Such trends
are key to understand how rocks recover after deformation and the state of
stress in around faults during the interseismic period. In this
presentation, I will show how laboratory rock physics experiments can
contribute to improve our understanding of why seismic wave speeds recover
after deformation, and what it tells about the stress state in the crust
following earthquakes. The essential result from my laboratory experiments
is that seismic wave speeds can recover very significantly (up to 10%) and
rapidly (over a few days) due to time-dependent microcrack closure, even
when the macroscopic stress state is maintained constant. This effect is
due to internal stress relaxation.