Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Models of seismic sources from local earthquakes

CRL seismological data are used to very precisely relocate earthquakes inside the CRL network. Multiplets, events that are located close to each other and have similar waveforms, are relocated in a relative sense with uncertainties of few tens of meters in all directions. This is possible because relative arrival times are picked using cross-correlation and cross-spectrum techniques with a precision of ~2msec.

With these relocated hypocenters, it is possible to very precisely image active structures because the uncertainties are now of the order or smaller than the dimension of the earthquake source itself instead of ~10 times larger for standard locations.

A joint analysis with focal mechanisms leads to a detailed study of the source of earthquakes of magnitude >3.5 for which aftershocks are present. Swarms of earthquakes that occur quite frequently in the area can also be studied with this technique.

The March-July 2001 earthquake sequence that include the Ml=4.7, April 8 2001 earthquake, 10km south of the town of Aigion was studied with this technique. Over 10 different multiplets made of 10-20 events were relocated. It was found that the main-shock was a normal faulting event with right lateral component. The active fault plane has a strike of ~220° and a dip of ~40° to the north-west. Although this focal mechanism is consistent with the general state of stress in the area, the identified active plane does not correspond to any active structure observed at the surface.

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Ecole normale supérieure
Rue Lhomond 24
75231 Paris
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