Task 1: Measuring fault damage and deriving elastic properties in natural damage zones

Leader: Isabelle MANIGHETTI (Géoazur) – Partners involved: Géoazur, Inria Sophia, Géoscience Montpellier, IPGP, LJAD, Arizona State University, UNAVCO, University of Pisa

Objectives

The Task 1 of the project aims at analysing damage faulting from kilometer- to meter-scales along the length of a significant number of parent faults with different properties, so as to examine the possible scaling relations between the parent faults and their damage zone(s), and quantify the 3D architecture of damage. We will then adapt mathematical homogenization theory to compute the effective elastic properties of the natural faulted damaged zones. The derived mechanical properties of damage zones will feed the numerical earthquake models developed in Task 2.

For the fault analysis, we target four sites:

  • Valley of Fire (VF, Nevada, strike-slip faults),
  • Waterpocket Monocline (WM, Utah, strike-slip and normal faults),
  • Bishop Tufs (BT, California, normal faults), and
  • Granite Dells (GD, Arizona, strike-slip and normal faults).

These sites are among the rare worldwide where multi-scale damage faulting can be well observed and analyzed in an extensive manner; in each site, damage indeed forms at the ground surface dense networks of fractures and faults of different lengths, distributed over large distances off-the parent fault traces. The four sites include both ancient and currently active faults, allowing comparing faults of different ages and damage zones exhumed from different depths. Parent faults have different slip modes and lengths and they offset different, yet homogeneous rock types, which allows assessing the possible influence of slip mode, length and material. In each site, we will analyze parent and damage faults using a variety of remote, airborne and field approaches and data.

First Results

The fault within the faults? A team of French geologists and seismo-tectonicists are investigating in the Southwest of the United States, published on Thursday December 13, 2018 by the Office for Science & Technology of the Embassy of France in the United States.