Speakers Club: Dr. Cedric Twardzik

Event Date: 

Thursday, January 21, 2016 - 2:00pm

Event Location: 

  • Webb Hall 1100

Dr. Cedric Twardzik will give a talk entitled Beyond kinematic modeling: Constraining the dynamic rupture parameters directly from the data at Speakers Club this Thursday at 2:00 PM in Webb Hall 1100.


The improvements of computer capabilities have allowed transitioning from a kinematic inversion approach (i.e., inferring the distribution of slip-rate functions on a fault) to a dynamic inversion approach (i.e., inferring the distribution of stresses on a fault). This has the advantage to offer a physics-based approach to study earthquake source processes. At the same time, the inversion procedure allows testing of thousands of different stress models and their capability to explain the observations. In this talk, I present the results obtained for two types of earthquakes. 
First, we have applied this state-of-art algorithm to study the 2014 Mw7.9 Rat Islands intermediate-depth (~110 km) earthquake. We show that this earthquake breaks the entire cold core of the subducting slab defined by the depth of the 600-650C isotherm. Our results also show that this earthquake has stress drop ranging from 2–7MPa and fracture energy ranging from 1–12MJ/m2 before we see a significant degradation of the waveform fit. Interestingly, these ranges are typical of large shallow earthquakes. 
In the second part of the talk, I will present the results for the 2014 Mw6.0 Napa Valley, California, earthquake and the 2004 Mw6.0 Parkfield, California, earthquake, both being shallow strike-slip earthquakes. The inversion finds a stress distribution that leads to a seismic moment and an average rupture speed close to the kinematic analyses of the two earthquakes. The main difference between the two earthquakes is the stress-drop, with a larger stress-drop (~10MPa) for the rather compact rupture of the Napa Valley earthquake, and a lower stress-drop (~4MPa) for the wider rupture of the Parkfield earthquake. This difference could highlight the fact that fault with long repeating times are stronger that fault with shorter repeating times.
Dr. Cedric Twardzik