WP 5.6 Paleo-stress fields and mechanics of faulting

Start date or starting event:

M0

Lead contractor:

UPMC

Participants:

UPMC

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Objectives:

Description of stress fields and understanding of the mechanical behaviour of an active seismogenic zone, the South Iceland seismic zone (SISZ), based on:

(a) Analysis of faulting in terms of geometry and mechanics based on systematic inversion of       fault slip data and focal mechanisms of earthquakes.

(b) Numerical modelling of deformation and stress-strain relationships.

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Inputs:

·         Existing fault slip data in the South Iceland seimic zone, to be compiled with additional detailed collection in the field close to the fault traces of the 2000 earthquakes.

·         GPS mapping of typical earthquake faults and fissures, for recent earthquakes and historical-prehistorical ones.

·          Existing aerial photographs in the South Iceland seimic zone.

·          Methodology / work description:

·         Inversion of fault slip data to obtain the stress tensor and of double-couple earthquake focal mechanisms (from the SIL-network) to obtain the stress tensor without choice among nodal planes.

·         Analysis of surface features of faults (mapping and geometrical analysis).

·         Numerical modelling softwares (distinct-element, finite-element).

A large number of data, geological and seismological has been acquired in the SISZ; that deserve detailed analysis, which has not been fully done yet, and provide a firm basis for a deeper understanding of the active, co-seismic deformation and hence for a better appraisal of the earthquake nucleation processes. The stress regimes that prevailed in the SISZ area during the last 2-3 millions years will be reconstructed based on systematic inversion of fault slip data, collected in the field, in order to be compared with the present-day stress regimes obtained from focal mechanisms of earthquakes. It is thus possible to determine how did the crustal stress change in space and time near a fault that was later activated during a major earthquake (e.g. the Árnes and Hestfjall faults of the major June 17 and 21 earthquakes, 2000). To this respect, a contribution to the mapping of the faults of the SISZ will be brought, as an attempt at combining mechanisms and structural pattern rather than a mere description of the fault traces. For this reason, our study of fault traces is focussed on selected areas where the brittle mechanisms can be reconstructed from both the geological and seismological observations. Numerical modelling will be carried out in a systematic way, in order to reproduce the actual deformation of the SISZ with simple boundary conditions and realistic thermal patterns. This modelling work will take advantage of both the large mass of data that already exists.

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Deliverables including cost of deliverable as percentage of total cost of the proposed project:

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Milestones: Delivery of the above items at the date indicated.